An Experimental Study Of Auditory Thresholds Of Adults For Warble Tone, Pure Tone, And Recorded Speech

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Content AN EXPERIMENTAL STUDY OF AUDITORY THRESHOLDS OF ADULTS FOR WARBLE TONE, PURE TONE, AND RECORDED SPEECH by R ichard L lew ellyn Hughes A D i s s e r t a t i o n P re se n te d to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In P a r t i a l F u l f i ll m e n t of the Requirem ents fo r the Degree DOCTOR OF PHILOSOPHY (Speech) June 1963 UNIVERSITY O F SO U TH ERN CALIFORNIA GRADUATE SCHOOL UNIVERSITY PARK LOS ANGELES 7 . CALIFORNIA This dissertation, written by R ichard L lew ellyn Hughes under the direction of hi,§.— Dissertation Com mittee, and approved by all its members, has been presented to and accepted by the Graduate School, in partial fulfillment of requirements for the degree of D O C T O R OF P H IL O S O P H Y Dean M 1 T T E E J Chairman TABLE OF CONTENTS C hapter Page I . THE PROBLEM AND INFORMATION RELATED TO THE FIELD OF STUDY................................................................ 1 I n t r o d u c t i o n ..................................................................... 1 The P r o b l e m ..................................................................... 1 Statem ent o f the p roblem ................................... 1 Im portance o f the P r o b l e m ................................... 2 D e f in i t io n s o f Terms U s e d ................................... 5 Normal h e a r i n g ........................................................... 5 Conductive h e a rin g lo s s ................................... 6 S e n so ry -n e u ra l h e a rin g lo ss ......................... 6 Moderate h e a rin g lo ss ........................................ 7 Severe h e a rin g lo s s ............................................. 7 Warble t o n e ................................................................ 7 I I . REVIEW OF THE LITERATURE............................................. 8 A udiom etric Methodology ........................................ 8 O b tain in g the t h r e s h o ld value .................... 8 C a lib r a te d speech a u d io m etry ......................... 15 C o r r e la tio n between speech and pure tone t h r e s h o l d ........................................ 18 Beats and R e la te d P h e n o m e n a .............................. 23 D e s c rip tio n o f Frequency M odulation . . . 28 S tu d ies R e la tin g to Frequency M o dulation..................................................................... 32 I I I . SUBJECTS, MATERIALS, EXPERIMENTAL, AND STATISTICAL PROCEDURES............................................. 37 E xperim ental D esign . ............................................. 37 S u b j e c t s ..................................................... 39 Normal s u b je c ts ...................................................... 39 H a rd -o f-h e a rin g s u b j e c t s ................................... 39 N on-audiom etric c r i t e r i a ................................... 42 E q u ip m e n t.......................................................................... 44 E xperim ental P ro c e d u re ............................................. 46 C a li b r a t i o n o f t e s t e q u i p m e n t ...... 49 Sequence o f s t i m u l i p r e s e n t a t i o n . . . . 49 I n s t r u c t i o n s to the s u b j e c t ........... 50 O btain ing the t o n a l th r e s h o ld v alue . . 52 O btain ing the speech r e c e p tio n t h r e s h o l d ................................................................ 54 Q u e stio n n a ire ........................................................... 56 i v S t a t i s t i c a l P ro c e d u re s. ........................................ 58 A udiom etric d a t a . .................................................. 58 S u b je ct q u e s t i o n n a i r e s ........................................ 59 IV. PRESENTATION AND ANALYSIS OF DATA.................... 60 M e a n s ............................................................................... 60 V a ria n c e .......................................................................... 61 The f r a t i o t e s t ....................................................... 61 S ignT ficance o f d i f f e r e n c e s d eterm ined by the t r a t i o t e s t . . . . 73 Sum o f the a b s o lu te d i f f e r e n c e s . . . . 79 Q u e stio n n a ire ........................................................... 80 I n t e r p r e t a t i o n of d a t a ........................................ 89 V. SUMMARY, CONCLUSIONS, AND IMPLICATIONS. . . 93 Sum m ary............................................................................... 93 P r o b l e m .......................................................................... 93 S u b j e c t s .......................................................................... 94 E q u ip m e n t ..................................................................... 94 E x p erim en tal p ro c e d u re s ................................... 95 A n a ly sis o f the d a t a ............................................. 95 Summary o f th e r e s u l t s ........................................ 96 C o n c l u s i o n s ..................................................................... 100 S ug gestions f o r F u rth e r Study ......................... 101 LITERATURE CITED................................................................ 103 APPENDIX 1 ............................................................................... 112 APPENDIX I I .......................................................................... 114 APPENDIX I I I .......................................................................... 117 APPENDIX I V .......................................................................... 120 APPENDIX V............................................................................... 123 APPENDIX V I .......................................................................... 126 APPENDIX V I I .......................................................................... 130 APPENDIX V III 131 LIST OF TABLES T able Page 1. D i s t r i b u t i o n o f e x p e rim e n ta l p o p u la tio n a c c o rd in g to c l a s s i f i c a t i o n of h e a r in g a c u i t y ............................................................ 41 2. D i s t r i b u t i o n o f m ed ica l d ia g n o s e s o f the h a r d - o f - h e a r i n g s u b j e c t s .......................... 43 3. D i s t r i b u t i o n o f norm al h e a r in g and h a r d - o f - h e a r i n g s u b j e c t s a c c o rd in g to a g e ................................................................................ 44 4. D i s t r i b u t i o n of norm al and h a r d - o f - h e a r in g s u b j e c t s a c c o rd in g t o sex . . . 45 5. Mean a sc e n d in g and d e sce n d in g pure tone earphone t h r e s h o ld s fo r r i g h t e a r s ...................................................................... 62 6. Mean a sc e n d in g and d e scen d in g pure tone earphone t h r e s h o ld s f o r l e f t e a r s ...................................................................... 63 7. Mean a sc e n d in g and d e sce n d in g w arble tone earphone t h r e s h o ld s f o r r i g h t e a r s ...................................................................... 64 8. Mean a s c e n d in g and d e sce n d in g w arble tone earphone th r e s h o ld s f o r l e f t e a r s ...................................................................... 65 9. Mean a s c e n d in g and d e sce n d in g w arble tone s o u n d f ie ld t h r e s h o l d s .............................. 66 10. Mean a sc e n d in g and d e scen d in g spondee t h r e s h o l d s .................................................. 67 11. Comparison o f mean th r e s h o ld s o b ta in e d by pure to n e s , w arble to n e s , and spondee w o r d s .................................................. 68 12. Means and v a r i a n c e s o f p u re tone and w arble to ne earphone t h r e s h o ld s f o r r i g h t e a r s ...................................................................... 69 v v i 13. Means and v a ria n c e s o f pure tone and w arble tone earphone t h r e s h o ld s fo r l e f t e a r s ...................................................................... 70 14. Means and v a ria n c e s o f w arble tone so u n d fie Id t h r e s h o l d s ........................................ 71 15. Means and v a ria n c e s of spondee t h r e s h o l d s ...................................................................... 72 16. F is h e r t v a lu e s o b ta in e d f o r g r e a t e s t d i f f e r e n c e s between mean ascen d in g and mean descen ding t h r e s h o l d s ....................... 75 17. G r e a te s t t: v a lu e s f o r mean d i f f e r e n c e s between t e s t c o n d itio n s "A" and " D " ................................................................. 76 18. G r e a te s t _t v a lu e s f o r mean d i f f e r e n c e s between t e s t c o n d itio n s M B" and " D " ................................................................ 77 19. G r e a te s t £ v a lu e s f o r mean d i f f e r e n c e s betw een t e s t c o n d itio n s M CM and "E" . . 78 20. S u b je c t re s p o n se s to q u e s tio n n a ir e number o n e ...................................................................... 86 21. S u b je c t re s p o n se s to q u e s tio n n a ir e number tw o...................................................................... 87 22. " F i r s t p r e f e r e n c e " re sp o n se s to q u e s t io n n a ir e number t h r e e . . 88 LIST OF FIGURES F ig u re Page 1. A c o u stic spectrum of a 1000 cps w arble tone m odulated a t fiv e p e r cent w ith a s i x cy cle r a t e .................... 31 2. Diagram of the e x p e rim e n ta l d e sig n . . . . 38 3. Block diagram o f the e x p e rim e n ta l e q u i p m e n t ..................................................................... 47 4. Sum o f the a b so lu te d if f e r e n c e s between ascen ding and descending th r e s h o ld s fo r group 1 ........................................ 81 5. Sum o f the a b so lu te d i f f e r e n c e s between ascen din g and descending th r e s h o ld s fo r group I I ................................... 82 6. Sum o f the a b so lu te d i f f e r e n c e s between ascendin g and descending th r e s h o ld s f o r group I I I .................................... 83 7. Sum of the a b so lu te d i f f e r e n c e s between ascen din g and descending th r e s h o ld s fo r group I V .................................... 84 8. Sum of the a b so lu te d i f f e r e n c e s between ascen din g and descending t h r e s h o ld s f o r group V........................................ 85 v i i CHAPTER I THE PROBLEM AND INFORMATION RELATED TO THE FIELD OF STUDY I n tr o d u c tio n P sy ch o m e trists are in g e n e ra l agreement w ith T hornd ike's maxim (92, p. 16) t h a t "w hatever e x i s t s a t a l l , e x i s t s in some am ount." Attem pts to q u a n tify t h a t which e x i s t s lead to measurement. Measurement i t s e l f i s simply the process o f a s s ig n in g numbers to some d is c rim in a b le a sp ec t of e vents acco rd in g to a s e t of r u l e s . (80, p. 176) In e s t a b l i s h i n g an isom orphic r e l a t i o n s h i p between a n um erical system and the b e h av io r under i n v e s t i g a t i o n a s c a le is c re a te d . In m easuring re sp o n se s to a c o u s tic s t im u li, s c a le s were developed to gauge a u d ito ry a c u ity . Pure tone s t i m u l i have t r a d i t i o n a l l y been employed to a sse ss a u d ito ry f u n c tio n . However, r e l a t i v e l y l i t t l e i n v e s ti g a t i o n o f th e use of frequency m odulated pure to nes in h e a rin g assessm ent has been accom plished. This study was undertaken to compare th e a u d itio n of a d u lts w ith and w ith o u t normal a u d ito ry th re s h o ld s by means o f th re e methods of th r e s h o ld p r e s e n t a t i o n (pure to n e s , w arble to n e s, and rec o rd ed sp eech ). The Problem Statem ent o f the p roblem . This study was designed 2 to determ ine w hether d if f e r e n c e s e x i s t among the a u d ito r y th r e s h o ld resp o n se s o f two groups o f s u b je c ts (normal h e a rin g and h a r d - o f - h e a r in g a d u lt s ) to th re e c l i n i c a l s t i m u l i (pure to n e s , w arble to n e s , and re c o rd e d spondee words) p re s e n te d under two c o n d itio n s (earphones and sound f i e l d ) . The fo llo w in g s p e c i f i c q u e stio n s were su g g e ste d by the problem : (1) Do d if f e r e n c e s e x i s t in th r e s h o ld v a lu e s f o r pure to n es and w arble to n es p r e s e n te d by e a r phones? (2) Do d i f f e r e n c e s e x i s t in th r e s h o ld v a lu e s fo r w arble to nes and rec o rd ed spondaic words p re s e n te d by e a r phones? (3) Do d i f f e r e n c e s e x i s t in th r e s h o ld v a lu e s fo r w arble to n es and re c o rd e d spondaic words p re s e n te d in a sound f i e l d ? (4) Does the type o f h e a rin g lo s s c o n t r i bute to any v a r i a t i o n s in th r e s h o ld v a lu e s among the s tim u li? (5) Does the degree of h e a rin g lo s s c o n tr ib u te to any v a r i a t i o n s in th re s h o ld v a lu e s among th e s tim u li? (6) Do th e th r e s h o ld v a lu e s o b ta in e d u sin g the s e l e c te d s t i m u l i d i f f e r s i g n i f i c a n t l y fo r any of the fre q u e n c ie s te s te d ? Im portance o f the Problem Stevens and Davis (85, p. 17) c a u tio n t h a t a c o ntin uou s ste a d y tone d e liv e r e d i n a r e s t r i c t e d sound f i e l d such as a room r a p id ly e s t a b l i s h e s a p a t t e r n of sta n d in g waves. This i n te r f e r e n c e phenomenon p r e s e n t s a 3 p e rp le x in g problem in o b je c tiv e r e v e r b e r a t io n measurements in which e x p e rim e n ta l sound decay curves dem onstrate c o n s id e ra b le d i s p a r i t y from t h e o r e t i c a l v a lu e s . (54, p . 127) The sta n d in g wave phenomenon makes i t im p ossible to d e t e r mine the i n t e n s i t y o f a tone a t any g iven p o in t i n the room j u s t by knowing the i n t e n s i t y a t i t s so u rc e. (85, p . 16) The p re s s u re am plitude a t any p o in t rem ains con s t a n t w ith time b u t w ith in the e n c lo su re an i n t e r f e r e n c e p a t t e r n i s c re a te d (by the a d d itio n or s u b t r a c t io n of energy r e f l e c t e d from the e n c lo s in g w a lls ) (110, p . 265) by which the p r e s s u r e am plitudes b e a r no c o n s i s t e n t r e l a t i o n to the d i s ta n c e s o f the v a rio u s p o in ts measured from the s o u rc e . (5, p. 563) Sabine (81, p. 149) n o te s t h a t the i n t e n s i t y of a continuous ste a d y tone measured a t i t s source was l e s s th an a t a d is ta n c e of fiv e f e e t from the s o u rc e . However, in sound f i e l d th re s h o ld measurement the i n t e n s i t y measured a t any p o in t in an e n c lo s u re must p o sse ss a v alue r e l a t i v e to the d is ta n c e from th e source w ith o u t the e f f e c t s of an i n te r f e r e n c e p a t t e r n . Thus, the use of pure tones in a sound f i e l d s e t t i n g f o r the d e te rm in a tio n of d i s c r e t e frequency h e a r ing th r e s h o ld s i s n e g ated by the s ta n d in g wave phenomenon and i t s consequences. However, the d e s i r a b i l i t y o f such h e a rin g th r e s h o ld measurement i s obvious in those s i t u a t i o n s where p r e s e n t a t i o n of the pure tone s t i m u l i through 4 earphones i s im p r a c tic a l. The need fo r a stim u lu s t h a t does n o t produce s ta n d in g waves would be of p r a c t i c a l v a lu e in a group t e s t i n g s i t u a t i o n where a la rg e p o p u la tio n could be e v a lu a te d in a sound f i e l d s e t t i n g . F urth erm o re, a sound- f i e l d t e s t environm ent r e f l e c t s a r e a l i s t i c l i s t e n i n g s i t u a t i o n t h a t may o f f e r a d d i t i o n a l in fo rm a tio n re g a rd in g human a u d ito ry fu n c tio n . The c u r r e n t p rocedure employed to e v a lu a te the perform ance o f a h e a rin g a id has n o t changed s i g n i f i c a n t l y sin c e i t was f i r s t su g g ested by C a rh a rt. (13) B a s ic a lly , the procedure r e q u i r e s a com parative a p p r a i s a l of sound- f i e l d speech th re s h o ld s and d is c r im i n a t io n sc o re s o b ta in e d w ith and w ith o u t a h e a rin g a id . Pure tone measurements in a sound f i e l d would be o f g r e a t v a lu e i n d e te rm in in g the frequency c h a r a c t e r i s t i c of a h e a rin g a id worn by a p a t i e n t . S im ila r ly , the h e a rin g a i d 's a c o u s tic g a in f o r each frequency could a ls o be a s s e s s e d . Because no sta n d in g waves are produced by a f r e quency m odulated pure tone when g e n e ra te d in a room, i t s use as a stim u lu s fo r s o u n d fie ld frequency th r e s h o ld measurements i s i n t r i g u i n g . Furtherm o re, the p u ls in g or su rg in g n a tu re of a frequency m odulated tone su g g e sts a use in those t e s t s i t u a t i o n s where the s u b j e c t has d i f f i c u l t y d i s t in g u i s h in g between the t e s t stim u lu s and an i n te r f e r e n c e phenomenon such as t i n n i t u s . H e lle r and Anderman (47, p . 52) s t a t e t h a t th e p a t i e n t ' s " a c o u s t i c a t t e n t i o n " i s more r e a d i l y h e ld by frequen cy m odulated t e s t to n e s . An i n v e s t i g a t i o n o f the s i n u s o i d a l freq uency m odulated pure tone as an a d ju n c tiv e method f o r the a p p r a i s a l o f h e a rin g t h r e s h o ld s i s t h e r e f o r e c o n sid e re d s i g n i f i c a n t . A rev iew of the l i t e r a t u r e p e r t i n e n t t o th e p re s e n t stu d y has r e v e a le d a c o n tin u in g se a rc h f o r a c o u s t i c s tim u li and th r e s h o ld e x p lo r a ti o n te c h n iq u e s t h a t e n a b le the c l i n i c i a n to i d e n t i f y h e a rin g th r e s h o ld a c c u r a t e l y and r e l i a b ly w ith an economy of tim e. In view o f th e l im i te d n a tu r e o f pure to n es in th r e s h o ld a p p r a i s a l t h i s stud y un d erto o k to t e s t th e v a l i d i t y o f a s i n u s o i d a l freq u en cy m odulated pure tone (w arble to n e) as a c l i n i c a l t o o l . D e f in i t io n s o f Terms Used Normal h e a r i n g . A judgm ent of norm al h e a r in g i s b ased on th r e s h o ld re s p o n s e . Because any resp o n se ten d s to vary w i t h in a s u b je c t r e l a t i v e to even s h o r t p e r io d s o f time and a ls o from s u b j e c t to s u b j e c t , th r e s h o ld s have emerged as s t a t i s t i c a l v a lu e s . The norm al a b s o lu te th r e s h o ld i s a v a lu e o b ta in e d from a s t a t i s t i c a l sam pling o f a p a r t i c u l a r p o p u l a t i o n . (6, 18, 35, 36, 45, 84) The a u d io m e tric v a lu e of 0 dB on th e h e a rin g lo s s d i a l o f the audiom eter r e p r e s e n t s a measure o f the c e n t r a l tendency o f the d i s t r i b u t i o n curve produced by the popu l a t i o n e v a lu a te d in the U nited S ta te s P u b lic H ealth H earing Survey. (6) This v a lu e , b ein g s t a t i s t i c a l in o r i g i n im p lie s t h a t norm al h e a rin g i s r e p r e s e n te d by a range o f re sp o n se s above and below 0 dB. For the purpose o f t h i s stu d y , a s u b je c t was judged to have norm al h e a rin g i f h i s a u d io m etric respon se f e l l w e ll w ith in the norm al range o f th r e s h o ld v a lu e s . T h e re fo re , a s u b je c t was c o n sid ere d to have norm al h e a rin g i f he d em o nstrated a pure tone a i r co n d u ctio n th re s h o ld t h a t d id n o t exceed a lo ss of 10 dB in any o ctave from 250 c y c le s per second to and in c lu d in g 4,000 cps. Conductive h e a rin g l o s s . A s u b je c t was judged to have a con ductive h e a rin g impairment i f by c o n v e n tio n a l pure tone a u d ito r y t e s t s h i s a i r c o n d u ctio n , bone conduc t i o n gap amounts to f i f t y p er c en t or more o f the a i r cond uction lo ss a t any octave from 250 cps to and in c l u d ing 4,000 cps. Each judgment was confirm ed by o t o l o g i c a l d i a g n o s i s . S e n so ry -n e u ra 1 h e a rin g l o s s . The term se n so ry - n e u r a l h e a rin g lo s s has been r e c e n t l y su g g ested to re p la c e the c l a s s i f i c a t i o n "nerve l o s s . " (63, p. 1273) The use of t h i s l a t t e r term im p lie s c o c h le a r and r e t r o - c o c h l e a r e t i o l o g y w ith o u t c o n fin in g the p a th o lo g ic focus to the a c o u s tic n e rv e . A s e n s o r y -n e u r a 1 lo ss was judged to e x i s t i f the 7 s u b je c t dem on strated a pure tone a i r con d u ctio n th r e s h o ld t h a t d id n o t exceed h i s pure tone bone c o n d u ctio n t h r e s h o ld by more than 5 dB i n any o ctav e from 250 to 4,000 cps. Each judgment was a g ain confirm ed by o t o l o g i c a l d ia g n o s is . Moderate h e a rin g l o s s . The degree o f h e a rin g im pairm ent dem onstrated by an a i r con d u ctio n lo s s amount ing to no l e s s th an 35 dB and no g r e a t e r th an 60 dB i n a t l e a s t fo u r o f the fiv e fre q u e n c ie s t e s t e d (250 cps to 4,000 cps) was judged a m oderate h e a rin g l o s s . Severe h e a rin g l o s s . For the purpose o f t h i s study a sev ere h e a rin g lo s s was d e fin e d as a pure tone a i r c o n d u ctio n th r e s h o ld t h a t exceeded 60 dB f o r a t l e a s t fo u r o f th e t e s t fre q u e n c ie s from 250 cps to 4,00 0 cps. Warble t o n e . Warble tone i s a p o p u la r d e s c r i p t i v e term a p p lie d to the phenomenon of s i n u s o i d a l frequency m o d u la tio n . (47, p. 52) This stim u lu s i s a complex b e a t ing sound p a t t e r n prov id ed by a s i g n a l g e n e r a to r desig n ed to produce a p e r io d ic o s c i l l a t i o n w ith in a r e s t r i c t e d and r e g u la b le frequency ra n g e . The w arble tone employed in t h i s stud y was g e n e ra te d by a com m ercially a v a i la b l e in stru m e n t capable of a d a p tin g the pure tone o u tp u t o f an au diom eter. CHAPTER I I REVIEW OF THE LITERATURE A udiom etric Methodology O b tainin g the t o n a l th r e s h o ld v a l u e . T hreshold audiom etry i s a c l i n i c a l a p p l i c a t i o n o f the c l a s s i c a l p sy c h o p h y sic a l method of l i m i t s ( a ls o known as the method o f minimal changes or the method of s e r i a l e x p lo r a ti o n ) in which the th re s h o ld i s d e fin e d as t h a t v a lu e midway between the ascending and descen d in g th r e s h o ld s where the s u b je c t responds to a t l e a s t 50 p e r c en t of the stim u lu s p r e s e n t a t i o n s . (49, p. 12) The te c h n iq u e o f the method of l i m i t s i s a p p lie d in d e te rm in in g the a u d ito r y th r e s h o ld in the fo llo w in g manner: A t e s t tone from a c a l i b r a t e d and c o n tr o l le d sound source i s p re s e n te d a t a c l e a r l y a u d ib le i n t e n s i t y l e v e l which i s th en p r o g r e s s i v e l y d ecreased in sm all i n t e n s i t y i n t e r v a l s u n t i l i t i s no longer h e a rd . The procedure i s th en r e v e r s e d in which the i n t e n s i t y i s in c re a s e d from a p o in t below th r e s h o ld u n t i l the tone i s a g ain p e rc e iv e d . (34, p. 175; 94, p. 221) T h e o r e ti c a l ly , the th re s h o ld v a lu e l i e s somewhere between the l a s t a u d ib le and the f i r s t in a u d ib le p r e s e n t a t i o n of the descending s e r i e s or the l a s t in a u d ib le and the f i r s t a u d ib le p r e s e n t a t i o n o f the ascen din g s e r i e s . This time honored concept of a u d ito r y th r e s h o ld e x p lo r a ti o n i s 8 p r e d i c a t e d on the assum ption t h a t the s e n s i t i v i t y o f th e o b s e rv e r c o n s t a n t ly v a r i e s . (85, p. 43) T h e re fo re , the e s ta b lis h m e n t of a t h r e s h o ld v a lu e i s b ased on s e v e r a l m easurements from which a s t a t i s t i c a l e s tim a te i s d e riv e d . G u ilfo rd (41, p. I l l ) b e l i e v e s th e r e i s no s i n g l e stim u lu s v a lu e along any continuum below which a resp o n se n e v er o c cu rs and above which a resp o n se always o c c u r s . He su g g e s ts a " re g io n o f u n c e r t a i n t y " in which re s p o n se s to a stim u lu s occur o nly p a r t o f the tim e. Woodworth (112, p . 220) s t a t e s t h a t a stim u lu s must p o s s e s s a c e r t a i n s t r e n g t h in o rd e r to ach iev e a resp o n se and t h a t th r e s h o ld i s th e t r a n s i t i o n betw een a stim u lu s too weak to e f f e c t a resp o n se and a stim u lu s s tro n g enough to e l i c i t the r e s p o n s e . In u n p u b lish e d d a ta quoted by H irsh , ( 4 9 ,p . 103) R o s e n b lith and M ille r found the th r e s h o ld f o r a d e sce n d in g s e r i e s to be about fo u r d e c i b e l s lower th an t h a t f o r an a sce n d in g s e r i e s . T h e re fo re , i t i s custom ary to a c c e p t th e mean v a lu e o f th e l a s t resp o n se to th e d escen d in g s e r i e s and the f i r s t resp o n se to the ascen d in g s e r i e s as th e t h r e s h o ld v a lu e . As T hurstone (94, p . 323) s u g g e s ts , i t i s n e c e s s a ry to t r e a t the t h r e s h o ld v a lu e as a s t a t i s t i c a l measure s in c e th e s u b j e c t v a r i e s in h i s s e n s i t i v i t y . However, th e t r a d i t i o n a l p sy c h o p h y sic a l method of l i m i t s employed i n the e s t im a t i o n of a u d ito r y a c u ity im p lie s t h a t th e m agnitude o f th e s te p s betw een the s tim u lu s p r e s e n t a t i o n s should be sm all enough to p ro v id e 10 fo r a c c u ra te a p p r a i s a l o f the o b s e r v e r 's f l u c t u a t i o n s in s e n s i t i v i t y . (41, p. 115) T herefore i t i s n e c e s s a ry to p r e s e n t to the o b se rv e r a s e r i e s of stim u lu s l e v e ls which f a l l w ith in the range o f h i s moment to moment f l u c t u a t i o n s . I t may be reasoned t h a t i f th e s te p s between the stim u lu s p r e s e n t a t i o n s a re too la rg e the e s ta b lis h m e n t of an e x a c t v alue fo r the th r e s h o ld i s p re v e n te d . The fo llo w in g s tu d i e s o f f e r s tro n g evidence t h a t th e fiv e dB i n t e n s i t y s te p between stim u lu s v a lu e s used in c l i n i c a l audiom etry is la r g e r th an the co ntin uou s f l u c t u a t i o n s in the a u d ito r y a c u i ty of the o b s e rv e r. Myers & H a rris (69) conducted an experim ent in which they i n v e s ti g a t e d th e s h o r t- te r m f l u c t u a t i o n s o f a u d ito r y s e n s i t i v i t y . The a u d ito ry th re s h o ld s of th re e males were o b ta in e d fo r 11 d i f f e r e n t fr e q u e n c ie s . The s i g n a l was a p u lse tone 750 msec, in d u r a tio n . Each t o n a l p r e s e n t a ti o n d i f f e r e d by one d e c ib e l from the p re c e d in g to n e . Five descending and fiv e ascending th r e s h o ld s were o b ta in e d fo r each freq u en cy . A th r e s h o ld value was c a l c u la te d fo r each a s c e n t and d e s c e n t. The r e l e v a n t c o n c lu sio n o f th e stu d y was t h a t moment to moment f l u c t u a t i o n s of the a u d ito ry th r e s h o ld a re l e s s th an one d e c i b e l . The a u th o rs conclude t h a t t h i s t o t a l f l u c t u a t i o n i s . . . . "the r e s u l t of i n s t a b i l i t y in the s u b j e c t 's a tte n d in g and resp ond ing systems as w e ll as in h i s a u d ito ry system p r o p e r ." (69, p. 4) 11 In developing h is method of s in g le d e sc e n t group audiom etry, Ward (182, 183) r e p e a te d ly t e s t e d m i l i t a r y p e rso n n e l a t 500 cps and 4,000 cps u t i l i z i n g a c o n tin u o usly changing t r a i n of p u lse s as the s i g n a l . Two r a t e s c o n s is tin g of 1.5 and 2.25 p u ls e s p er second were combined w ith two a tt e n u a tio n s te p s of 1.5 dB and 3.9 dB. Each of th ese r e s u l t i n g c o n d itio n s was p re s e n te d fiv e tim es to each s u b je c t who was i n s t r u c t e d to r e p o r t the d is a p p e a r ance of the b e a t s . I t was found t h a t the fo ur c o n d itio n s of stim u lu s d e sce n t were e s s e n t i a l l y e q u al in r e l i a b i l i t y as judged by a sta n d ard d e v ia tio n of 1.7 dB among re p e a te d t e s t s . An i n v e s t i g a t i o n in to the s t a b i l i t y of a u d ito ry th re s h o ld s fo r 80 msec, c li c k s was conducted by Wertheimer. (105) He found t h a t the s ta n d a rd d e v ia tio n among t h r e s hold v a lu es w ith in one t e s t s e s s io n was of the o rd er of 0.7 d e c ib e l. Furtherm ore he r e p o rte d the average s ta n d ard d e v ia tio n of te n th re s h o ld s o b tain ed d u rin g a sin g le day was only 0.9 d e c ib e ls . An average sta n d a rd d e v ia tio n o f only 1.2 dB was found fo r d a il y th re s h o ld s o b tain ed over an e la p se of 23 su c c e ss iv e days. We may conclude from the foreg o in g s tu d ie s t h a t sin c e the v a r i a t i o n s in a u d ito ry s e n s i t i v i t y a re of a magnitude le s s than the c l a s s i c a l 5 dB s te p o f c l i n i c a l audiom etry i t i s im possible fo r the t e s t e r u sin g t h i s i n t e n s i t y i n t e r v a l , to determ ine an e x a c t measurement of 12 t h r e s h o l d . A sam pling rev iew o f the l i t e r a t u r e co n cerning the a p p r a i s a l of h e a rin g th r e s h o ld s d em o n stra te s the absence o f a s ta n d a r d iz e d audiom eter t e s t methodology. (11; 19, p. 118; 49, p. 112; 52; 72, p. 74; 100, p. 36) Reger (76) su g g e sts t h a t the p sy c h o p h y sic a l method of l i m i t s as em ployed by c l i n i c a l a u d io m e tr is ts f o r the d e te r m in a tio n of a u d ito r y th r e s h o ld s has been g r e a t l y a b b re v ia te d and m odi f i e d . He b e li e v e s s u f f i c i e n t j u s t i f i c a t i o n e x i s t s fo r such m o d if ic a tio n s sin c e the methodology r e q u i r e s t h a t the h e a rin g a p p r a i s a l be accom plished in a n o ise reduced environm ent in term s o f i n t e n s i t y s te p s approaching a j u s t n o tic e a b le d i f f e r e n c e and t h a t enough s u b je c t re sp o n se s a re o b ta in e d f o r each tone f o r s i g n i f i c a n t s t a t i s t i c a l a n a l y s i s . The a u d i o m e t r i s t , t h e r e f o r e , has through n e c e s s i t y , been com pelled to employ a th r e s h o ld t e s t i n g tech n iq u e from which a c c u ra te d e t e c t i o n of h e a rin g d e f e c t s could be achieved w ith a r e l a t i v e l y sm all e x p e n d itu re of tim e. H irsh (49, p. 108) su g g e sts t h a t in the absence of any a cc ep ted sta n d a rd te c h n iq u e , d if f e r e n c e s among t h r e s ho ld v a lu e s may be a t t r i b u t a b l e to the d i f f e r e n c e s among t h r e s h o ld d e te rm in a tio n methods. Acceptance o f H i r s h 's comment r e q u i r e s the a u d io m e t r i s t to d e v ise and adhere to a t e s t tech n iq u e t h a t encourages c o n s is te n c y in the e x p lo r a ti o n o f the o b s e rv e r's a u d ito r y th r e s h o ld . 13 An u n d e rs ta n d in g o f the a u d ito ry phenomena o f "on e f f e c t " and " a d a p ta tio n " a s s i s t s the a u d io m e tr is t to d e sig n a te c h n iq u e fo r the d e te rm in a tio n o f th r e s h o ld . Worded sim ply, the o n - e f f e c t i s the i n i t i a l and a ls o , most v ig o ro u s resp o n se o f the a u d ito r y system a t th e o n se t o f s t i m u l a t i o n . F u rth erm o re, when the stim u lu s i s p r o longed, the o n - e f f e c t of the system i s follow ed by a d e c re a se in s e n s i t i v i t y . This l a t t e r c o n d itio n i s termed a u d ito r y a d a p ta tio n . E arly i n v e s t i g a t i o n s o f the a c t io n p o t e n t i a l s o f the a u d ito r y system s o f anim als d em on strated the e x is te n c e o f th e s e phenomena. (20, 32, 88) Of more r e l e v a n t v a lu e to the p r e s e n t study a re the i n v e s t i g a t i o n s o f human a u d ito r y re sp o n se s in which the a d a p ta tio n o f s u b je c ts w ith norm al and im paired h e a rin g was e x te n s i v e l y e x p lo re d . (23, 50, 55) I t was, however, H a llp ik e and Hood (43) who s t r e s s e d th e c l i n i c a l r a m i f ic a t i o n s o f the phenomena in su g g e stin g a com bination o f o n - e f f e c t n o r m a lity and profound a d a p ta tio n . They proposed t h a t such a com bination i s n o t only dem on strated in the a d a p ta tio n o f a norm al e a r b u t a ls o in a r e c r u i t i n g e a r . In th e s e cases th e re ap pears to be an i n i t i a l resp o n se in which th e s u b je c t p e rc e iv e s a tone o f maximum lo u d n ess. However, i f the tone i s p ro lo n g ed , the i n i t i a l resp o n se r a p i d l y d e t e r i o r a t e s . A t t e n tio n must be drawn to the e x is te n c e o f extrem e a d a p ta tio n in c o c h le a r and n e u r a l l e s io n s w ith i t s v a rio u s speeds of o n se t and rec o v ery and accompanying 14 v a r i a t i o n s in r e s p e c t to the frequency o f the to n a l p r e s e n t a t i o n . (56, 57, 73) The c l i n i c a l im p lic a tio n s o f th e s e s t u d i e s p o in ts to the t h e o r e t i c a l and p r a c t i c a l l i m i t a t i o n s o f any a u d io m etric tech n iq u e which does n o t e l i c i t th e o n - e f f e c t in d e te rm in in g the unadapted a u d ito ry th r e s h o ld . An unknown amount o f a d a p ta tio n i s produced by a procedure in which an o n - e f f e c t i s evoked by an a u d ib le tone which i s su b se q u e n tly a tte n u a te d w ith o u t i n t e r r u p t i o n u n t i l the s i g n a l becomes in a u d ib le . M ille r and R o s e n b lith , as quoted by H irsh (48, p. 104) d is c o v e re d t h a t th r e s h o ld s o b ta in e d w ith a descending te c h n iq u e u sin g s u s ta in e d 4,000 cps to n es are as much as 15 dB h ig h e r th an the th r e s h o ld f o r s i m il a r to n es o b ta in e d by an ascending method. Furtherm ore they observed t h a t the d isc re p a n c y between ascending and descend ing t h r e s h o ld s in c re a s e d as the m agnitude of the i n i t i a l tone i n c r e a s e d . T h e re fo re , i t behooves the c l i n i c i a n to d e v ise a te c h n iq u e which o f f e r s the o b se rv e r d i s c r e t e t o n a l p r e s e n t a t i o n s each of which are of s h o r t d u r a tio n and s u f f i c i e n t l y i s o l a t e d in time from one a n o th e r. An i n t e r e s t i n g v a r i a t i o n o f th e c o n v e n tio n a l method of th r e s h o ld e x p lo r a ti o n i s th e " p u ls e - to n e " te c h n iq u e . (33) This method c a l l s f o r the p r e s e n t a t i o n o f groups one, two, or th re e pure tone b u r s t s a t v a ry in g sound l e v e l s . Ihe o b se rv e r i s r e q u ir e d to i n d ic a t e the number 15 o f t o n a l p u ls e s w ith in each group he h e a r s . The l a s t l e v e l a t which the s u b je c t c o r r e c t l y i d e n t i f i e s the number of p u ls e s w ith in the group i s taken as th r e s h o ld . C a lib r a te d speech a u d io m etry . One of the most u s e f u l advances in c l i n i c a l audiom etry was the i n tr o d u c tio n o f c a l i b r a t e d speech. In fo rm a tio n o f m e rit can be o b tain ed when h e a rin g i s a s s e s s e d w ith p r o p e rly s ta n d a r d iz e d speech sam ples. Not only does speech t e s t i n g a f f o r d the d i a g n o s t i c i a n a g r e a t e r fund o f in fo rm a tio n on which to base h i s im p re ssio n s and l a t e r to a s s e s s the r e s u l t s of th era p y b u t a ls o , d e m o n stra te s i t s im portance in su g g e stin g g uides to the e d u c a tio n a l and r e h a b i l i t a t i v e management o f the p a t i e n t . Probably the f i r s t speech audiom eter was an i n s t r u ment p re s e n te d by B ryant (10) in 1904, which, u n d e rs ta n d a b ly , follow ed c lo s e l y on th e h e e ls o f the in v e n tio n of the E dison phonograph. This crude d ev ice u t i l i z e d a wax c y lin d e r on which were re c o rd e d sim ple m on o sy llab ic w ords. The t e s t item s were tr a n s m i t te d to the o b s e r v e r 's e a r s by s te th o s c o p ic tu b e s . The in stru m e n t was c a l le d an Acou- m eter b u t n e v er g ained g e n e r a l a c c e p ta n c e . Development of the speech audiom eter was la r g e ly abandoned u n t i l the l a t e n in e te e n tw e n tie s , when the W estern E l e c t r i c 4-A Audiometer appeared. (67) I t was the f i r s t e l e c t r i c in stru m e n t and employed a spring-wound t u r n t a b l e w ith a m agnetic pickup to which were a tta c h e d a 16 netw ork of twenty to f o r t y earphones fo r group t e s t i n g . Phonograph d i s c s were used on which were re c o rd e d l i s t s o f th re e d i g i t numbers. The spoken d i g i t s , one through s i x , and e i g h t , were u sed . In d is c u s s in g t h i s e a r l y t e s t , H irsh (48) f e e l s t h a t i t was m ainly a t e s t o f vowel r e c e p t i o n sin c e none o f the two d i g i t groups p o ssesse d the same vowel sound. He f e e l s a more d e t a i l e d t e s t i s i n d i c a te d i f the measure o f h e a rin g lo ss fo r speech i s to in c lu d e more th an an assessm ent o f h e a rin g fo r vowel so u n d s. The p o p u l a r i ty of the 4-C audiom eter in c r e a s e d . S ub sequ ently , a number of speech t e s t s were developed to measure the th r e s h o ld of i n t e l l i g i b i l i t y . (31, 68, 101) These t e s t s employed l i s t s o f e i t h e r numbers, words, nonsense s y l l a b l e s , or s e n te n c e s . However, none o f th e s e t e s t s won wide fa v o r. F l e tc h e r (26) and h i s a s s o c i a t e s a t the B e ll Telephone L a b o r a to r ie s conducted r e s e a r c h r e g a r d in g the a c o u s tic s of spoken language and i t s r e c e p t i o n by the human e a r . Encouraged by h i s c o n tr i b u ti o n s , o th e r w orkers began to approach th e stu d y o f h e a rin g t e s t i n g through the use o f speech samples more r i g o r o u s l y . Some of t h e i r i n v e s t i g a t i o n s p e r t i n e n t to t h i s study are p r e s e n te d be low. Wartime re s e a r c h conducted by Hudgins (51) and h i s a s s o c i a t e s a t the Psycho A cou stic L ab o rato ry of 17 Harvard U n iv e rs ity produced th e PAL A u ditory T ests Number 9 and Number 12 fo r d e te rm in in g th e speech r e c e p t i o n th r e s h o ld . The i n v e s t i g a t o r s rea so n e d t h a t four e s s e n t i a l in g r e d i e n t s a re n e c e s s a ry to th e c o n s t r u c t io n o f a v a l i d and r e l i a b l e measure o f h e a r in g f o r spdech. These c h a r a c t e r i s t i c s a r e : f a m i l i a r i t y o f th e t e s t ite m s, p h o n e tic d i s s i m i l a r i t y among the v a r io u s ite m s, norm al sam pling of E n g lish sounds, and hom ogeneity o f a u d i b i l i t y . A fte r c o n s id e ra b le e x p e r im e n ta tio n , 84 d i s s y l l a b i c words o f the spondee s t r e s s p a t t e r n were chosen. The s u b j e c t 's th r e s h o ld fo r each PAL t e s t i s e s t a b l i s h e d as the d e c i b e l l e v e l where 50 p er c e n t o f the t e s t item s a re u n d e rs to o d . F a lc o n e r (24) and Davis (25) i n v e s t i g a t e d the r e l i a b i l i t y w ith which 50 norm al h e a r in g and 94 h e a rin g im paired a d u lts could e s t a b l i s h t h e i r own T hreshold o f I n t e l l i g i b i l i t y fo r Connected D isco urse (TICD). The sample o f speech used in the TICD t e s t was a re c o rd e d r a d io b ro a d c a s t of F u lto n Lewis, J r . to which the s u b j e c t l i s t e n e d and v a r ie d the p r e s e n t a t i o n l e v e l by a d ju s tin g an a t t e n u a t o r . The s u b je c t was i n s t r u c t e d to s e l e c t the l e v e l a t which he j u s t b a r e ly u n d e rsto o d the c o n te n t of the m a t e r i a l . The th r e s h o ld s o b ta in e d in t h i s manner were compared to th ose d eterm in ed by PAL A ud ito ry T est No. 9. A s i g n i f i c a n t l y h ig h c o r r e l a t i o n was found to e x i s t between th e two t e s t s w ith a norm al h e a r in g p o p u la tio n . For the h a r d - o f - h e a r in g group, however, th e c o r r e l a t i o n 18 was lower and g r e a t e r d e v ia tio n s between the t e s t s o c c u r r e d . Thurlow (93) found t h a t i n d iv i d u a l h e a rin g lo s s e s f o r speech determ ined by A uditory T est No. 9, A u dito ry T est No. 12, the 4--C r e c o r d s , or the TICD t e s t c o r r e l a t e d v e ry c lo s e ly w ith one a n o th e r and t h a t only one o f them need be used in any c l i n i c a l r o u t i n e . E v e n tu a lly , the PAL T ests 9 and 12 were su p erseded by the C e n tr a l I n s t i t u t e fo r the Deaf t r a n s c r i p t i o n s W--1 and W--2. (7) These l a t e r word samples were s e l e c te d from the l a r g e r group employed i n the o ld e r t e s t s and were co n fin e d to very f a m i l i a r words which seemed s u i t a b l e fo r b o th c h ild r e n and a d u l t s . T h i r t y - s i x spondee words were chosen a f t e r th ey were found e x p e rim e n ta lly to be e q u a lly i n t e l l i g i b l e . In o rd e r to overcome the shortcom ings o f spondee words as a t e s t of speech r e c e p t i o n , H a rris (44, p. 401) m od ified the PB Word L i s t s p re p a re d by Egan. (22) Compari son of h i s m o dified PB word t e s t w ith spondee words de m o n stra te s t h a t sim u la te d d e a fn e ss above 1,000 cps red u c es spondee i n t e l l i g i b i l i t y by 25 p e r cen t w h ile PB word i n t e l l i g i b i l i t y i s reduced 80 p e r c e n t. I t was concluded t h a t the PB l i s t s do r e f l e c t h e a rin g lo s s e s in the h ig h e r frequency re g io n s of speech. C o r r e la tio n between speech and pure tone th r e s h o ld W ish a rt (111) f l a t l y r e j e c t s the e f f o r t s o f i n v e s t i g a t o r s 19 to examine the r e l a t i o n s h i p between a c u ity f o r pure ton es and f o r speech. He re a so n s t h a t the two t e s t s a c t u a l l y measure d i f f e r e n t prim ary a b i l i t i e s . On the o th e r hand, many i n v e s t i g a t o r s have o f f e r e d p r e d i c t i v e system s in an e f f o r t to c o r r e l a t e the f in d in g s o f pure tone and speech audio m etry . F l e tc h e r (26, p. 43) and h i s a s s o c i a t e s have devoted much of t h e i r work to t h i s problem . Study o f speech a u d i b i l i t y and i n t e l l i g i b i l i t y w ith v a rio u s fre q u e n c ie s f i l t e r e d o ut led him to d is c o v e r t h a t the a re a betw een 500 cps and 2,000 cps i s of s p e c i a l im portance to the h e a rin g o f speech. W ith t h i s e x p e rim e n ta l evidence i t was su g g e ste d t h a t an average o f th e s e o c ta v e s would y i e l d the most a c c u ra te p r e d i c a t i o n o f h e a rin g f o r speech. Sabine (82) o f f e r e d q u ite a d i f f e r e n t p r e d i c t i v e in stru m e n t founded on the r e l a t i o n between speech r e c e p t i o n and th e a b i l i t y o f the a u d ito r y system to make d i s c r im i n a t io n s fo r loudness and p i t c h w ith the i n t e n s i t y and frequency re g io n s found in speech p ro d u c tio n . An e s tim a te o f the d e c ib e l lo s s a t each frequency from 128 cps to 4,096 cps n e c e s s a ry fo r t o t a l im pairm ent fo r speech r e c e p t i o n se rv e s as a b a s i s . This a u d ito r y a re a was d iv id e d i n to segments m easuring one octave wide by 5 dB h ig h . Each segment was a ssig n e d a w eight a cc o rd in g to the p e rc e n ta g e i t h e ld of the t o t a l d is c r im in a b le i n t e n s i t y d i f f e r e n c e s over the whole a u d ito r y r e g io n . He computed 20 t h a t the e a r could d i s c r im i n a t e a t o t a l o f 1,547 d i f f e r e n t i n t e n s i t y changes w ith in the u s e f u l range f o r speech . The number o f d is c r im in a b le freq u en cy d i f f e r e n c e s w ith in each segment was h e ld to be s i m i l a r . T h e re fo re , th e p e rc e n ta g e r a t i n g o f the a b i l i t y to p e rc e iv e speech i s based upon the assum ption t h a t i t i s a f u n c tio n of the number of d i s c r i m inable s te p s o f p i t c h and loudness a v a i la b l e to the im paired a u d ito r y system . In a l a t e r v e r s io n , the v a lu e s a ssig n e d to each segment were a r b i t r a r i l y a l t e r e d to conform w ith th e r e s u l t s of the B e ll L ab o rato ry s t u d i e s on speech i n t e l l i g i b i l i t y as a f u n c tio n o f i n t e n s i t y and frequency f i l t e r i n g . (2) Fowler (29) o f f e r e d a system of c a l c u l a t i n g h e a rin g lo s s fo r speech from th e pure tone audiogram . His system was e s t a b l i s h e d e m p i r ic a ll y from d a ta o b ta in e d from s e v e r a l hundred p a t i e n t s who were a s s e s s e d as to the correspondence betw een t h e i r speech r e c e p t i o n and pure tone s c o r e s . He a p p lie d w e ig h ts o f 15, 25, 30, 25 and 15 to the t h r e s h o ld l e v e ls a t 500, 1,000, 2 ,000 , 3,000, and 4.000 cps r e s p e c t i v e l y . A w eigh ted d e c i b e l lo s s fo r speech was computed m erely by adding th e sco re o b ta in e d by m u l t i p ly in g the pure tone lo s s e s by the a p p r o p r ia te w eig h ts and d iv id in g by 100. In a l a t e r v e r s io n o f th e method the w eig h ts were m o dified to 15, 30, 40 and 15 f o r the o c ta v es 500, 1,000, 2.000 and 4,000 c p s. A th e o ry was a ls o advanced h ere t h a t 21 r e c ru itm e n t tends to reduce the i n d i v i d u a l 's h an dicap fo r p e rc e iv in g speech by making the loudness o f c o n v e r s a tio n a l speech alm ost as loud as t h a t p e rc e iv e d by the norm al e a r . A djustm ents, to account f o r the in flu e n c e o f r e c r u itm e n t were in c lu d e d in the method of w e ig h tin g . (30) An a n a ly s is o f the c u r r e n t system approved by the American M edical A s s o c ia tio n (3) f o r computing lo s s fo r speech from pure tone audiograms r e v e a l s i t to be the p ro d u c t of a s e r i e s o f compromises. S a b in e 's o r i g i n a l concept t h a t speech r e c e p t i o n r e s t s on the number of p sy c h o a c o u stic d i s c r im i n a t io n s rem aining to the handicapped e a r was q u ic k ly m o dified to in c lu d e th e g r e a t e r c o n t r i b u tio n of the more i n f l u e n t i a l f r e q u e n c ie s . This method was adopted b u t f i r s t a l t e r e d by the American M edical A s s o c ia tio n in 1943 to in clu d e F o w le r's proposed w e ig h ts . However, t h i s most r e c e n t A.M.A. v e rs io n no lo n g er r e f l e c t s S a b in e 's o r i g i n a l th e o ry b u t has been adapted to conform w ith F o w le r's w eights f o r p e rc e n ta g e lo s s fo r speech r e c e p tio n a b i l i t y . F le tc h e r (28) co n tin u ed h i s e x p e rim e n ta l s t u d i e s of the r e l a t i o n between h e a rin g lo s s fo r speech and pure tone f in d in g s . He o f f e r s a form ula b ased on the d e te r m i n a tio n of the r e l a t i v e c o n t r i b u t i o n o f d i f f e r e n t f r e q u e n c ie s. In a t e s t o f 165 e a rs w ith d i f f e r e n t d egrees of impairm ent he was a b le t o e s t a b l i s h a system of d i f f e r e n t i a l w e ig h tin g which evolved i n to the sim ple 22 p r i n c i p l e of av erag in g the two b e s t re sp o n se s f o r the o c ta v es from 500 cps to 2,000 cps. F l e tc h e r (27, p. 442) o f f e r s s t i l l a n o th e r method employing a d i f f e r e n t system o f freq uency w e ig h tin g . This system produces a p e rc e n ta g e lo s s o f h e a rin g f o r speech by u sin g the f a c t o r s 0 .003, 0.037, 0 .1 3 , 0 .2 5 , 0 .3 0 , 0 .2 3 , and 0.05 f o r each o f the o c ta v es from 125 to 8,000 cps r e s p e c t i v e l y . In a r a t h e r co m plicated and tim e consuming com putation the d e c ib e l d if f e r e n c e a t each frequ ency between the two e a r s i s f ig u r e d . Depending on the d e c ib e l d i f f e r e n t i a l an a p p r o p r ia te v a lu e i s added to the d e c ib e l lo s s o f the b e t t e r e a r . This sum i s th en m u l t i p l i e d by the a p p ro p ria te w eight f o r each frequency and f i n a l l y the p ro d u c ts f o r each o f the o c ta v es a re added t o g e th e r to give the b i n a u r a l or " e f f e c t i v e h e a r in g lo s s " f o r speech. The r e s u l t s o f an i n v e s t i g a t i o n by C a rh a rt (14) of 300 men a t the Deshon G eneral H o s p ita l A ural R e h a b i l i t a t i o n S ervice i n d ic a t e a d e f i n i t e in te rd ep e n d en c e between lo s s e s f o r pure to n es and f o r speech. Five e x p e rim e n ta l groups were assem bled on the b a s i s o f t h e i r pure tone a i r con d u ctio n c o n f i g u r a ti o n . An average o f th e b e t t e r pure tone th r e s h o ld s f o r each e a r a t 512, 1024, and 2048 cps was compared in each s u b je c t to h i s b i n a u r a l th r e s h o ld fo r d i s s y l l a b i c words p r e s e n te d by m onito red l iv e v o ic e . I t was found t h a t w h ile th e re i s a h ig h c o r r e l a t i o n between the two m easures, i n d i v i d u a l s u b je c ts o f te n dem onstrated 23 c o n s id e r a b le d i s c r e p a n c i e s . In a d i s c u s s i o n o f cases where lack of c o r r e l a t i o n occurs between pure tone and speech r e c e p t i o n th r e s h o ld s J u e r s (59) su g g e sts t h a t a g r e a t e r lo s s fo r speech th an fo r pure to n es i s common in s e n s o r y - n e u r a l d e a f n e s s . He contends t h a t the p h o n e tic elem ents o f the t e s t item s v a ry in i n t e n s i t y . Some o f th e s e lo u d er elem ents f a l l w i t h in the r e c r u i t i n g range of a n e u r a l l y d eafened e a r w h ile o th e r phonemes may n o t be w i th in the range of a u d i b i l i t y . H a rris (46) proposed a n o th e r p r e d i c t i v e procedure based on the s t a t i s t i c a l m a n ip u la tio n known as the M ultiple R e g re ssio n p r e d i c t i o n e q u a tio n . Pure tone a u d io m etric v a lu e s as w e ll as a r t i c u l a t i o n sc o re s u sin g the CID A uditory T est W--22 were o b ta in e d on 197 p a r t i a l l y d e f e c t i v e e a r s . W eights were s t a t i s t i c a l l y d e v ised and a p p lie d to each o f the fre q u e n c ie s 500, 1,000, 2,000 , 4,000 and 6,000 cps. I t was dem o n strated t h a t no one p r e d i c t i v e method was b e s t s u i t e d f o r a l l a u d io m e tric p a t t e r n s . The i n v e s t i g a t o r s concluded t h a t the most s t a b l e method fo r p r e d i c t i n g h e a rin g lo s s f o r speech was the mean v a lu e of the M u ltip le R e g re ssio n e q u a tio n p r e d i c t i o n and the average of the th r e e speech fre q u e n c ie s method. B eats and R e la te d Phenomena Two pure to n es i d e n t i c a l in freq uency p re s e n te d 24 s im u lta n e o u s ly to an e a r w i l l produce a tone of the same frequency b u t of v a ry in g s e n s a tio n s of loudness depending upon the phase r e l a t i o n s h i p o f the component to n e s . Maximal loudness i s g e n e ra te d by an " in - p h a s e " r e l a t i o n s h i p w h ile s i l e n c e i s o bserved when the to n es a re co m pletely out o f p h a se. On the o th e r hand, two to n es d i f f e r i n g only s l i g h t l y in freq u en cy when sounded t o g e th e r w i l l g e n e ra te a number o f b e a ts p e r second e q u a l to the d i f f e r e n c e betw een the two components. (85, p. 241) Hie independent d is c o v e r i e s o f t h i s phenomenon were p u b lis h e d in the f i r s t h a l f o f the 18th Century by T o r t i n i , Sorge and Romieu. (58) Wever (106, p. 405) d isc o v e re d t h a t as the s e p a r a t io n in frequency grows l a r g e r between two pure to n es p re s e n te d s im u lta n e o u s ly to the e a r , the r e s u l t a n t sounds a re d i s tin g u is h e d by th re e s ta g e s o f the b e a t phenomenon. The f i r s t sta g e i s c h a r a c t e r i z e d by a s in g le tone whose lo u d ness waxes and wanes. A lthough b e a ts as slow as one in two m inutes have been h e a rd , only the l i m i t a t i o n s o f the a p p a ra tu s and the o b s e r v e r 's p a tie n c e p re v e n t th e p e rc e p t i o n of slow er b e a t s . However, the r o l l i n g n a tu r e o f the b e a ts o f t h i s sta g e a re most e v id e n t in the re g io n o f one to s i x b e a ts p er second. As the b e a t- f re q u e n c y i s i n c re a s e d beyond s i x or seven b e a ts p e r second, th e su rg in g of loudness y i e l d s to the p e rc e p tio n o f i s o l a t e d im pulses c h a r a c t e r i s t i c of Stage I I . There are no w e ll d e fin e d b o u n d a rie s to any o f the s ta g e s o f t h i s e x p e rie n c e . B efore 25 th e in te r m i t t a n c e o f Stage I I d is a p p e a rs th e roughness c h a r a c t e r i s t i c of Stage I I I i s e v id e n t. This te rm in a l sta g e develops a t a p p ro x im ately 166 b e a ts p e r second and i s prom inent as a rough t o n a l s e n s a tio n u n t i l i t d im i n is h e s to the p o in t where su b se q u e n tly two prim ary to nes are h e a rd . The two to n es become e v id e n t when the frequency s e p a r a t io n amounts to about 356 cp s. In 1877, Thompson (90) observed the b e a t e f f e c t when each of two s l i g h t l y d i f f e r i n g fre q u e n c ie s were p re s e n te d to each e a r . Subsequent i n v e s t i g a t i o n (91) led him to d e s c rib e the " b in a u r a l s h i f t phenomenon" (108, p. 427) in which he observed th e t o n a l s e n s a tio n to wander from e a r to e a r . L a te r i n v e s t i g a t o r s observed and d e s c rib e d th e same phenomenon. (70, 87) Lane (64) p o s t u l a t e d t h a t the b e a ts o r i g i n a t e in the e a r to which the weaker tone i s p r e s e n te d . The more in te n s e frequency conducted a c ro ss the head to t h i s e a r e s t a b l i s h e s the b e a t-p ro d u c in g i n t e r f e r e n c e . Myers and W ilson (71) a ls o a c c e p t the view t h a t to n a l d isp lac em e n t i s p r o p o r t io n a l to the i n t e n s i t i v e d i f f e r e n c e o f the two e a r s . On the o th e r hand, P e te rs o n (74) and S tew art (87) a f t e r more e x a c tin g e x p e rim e n ta tio n fav o r the h y p o th e s is t h a t p e r c e p tio n o f phase d if f e r e n c e s acco u n ts f o r the b i n a u r a l s h i f t phenomenon. L a te r work inv o lv ed the d e te r m in a tio n of the upper frequency l i m i t s a t which b i n a u r a l b e a ts a re p e rc e iv e d . L im its were o b ta in e d as low as 640 cps by R ayleig h (75) and as h igh 26 as 4,000 cps by Trimple (96) w ith o th e r w orkers (64, 66, 86, 108) r e p o r t i n g v a lu e s in betw een. In the l a t e s t r e p o r t o f i n v e s t i g a t i o n i n t o th e freq u en cy l i m i t s of b i n a u r a l b e a t s , L i c k l i d e r , W ebster and Hedlun (65, p . 470) summarize some of th e v a r i a b l e s involved in t h i s m easure ment. They observe t h a t the d e te rm in a tio n o f the upper l im i t i s p r o p o r t io n a l to the i n t e n s i t y o f the stim u lu s to n e s . B in a u ra l b e a ts can be h eard beyond 1,000 cps i f the frequency d i f f e r e n c e between th e two to nes i s sm a ll. F urtherm ore, the l i s t e n e r must be extrem ely a t t e n t i v e to h i s ta s k sin c e the o b s e r v a tio n of the b i n a u r a l b e a t e f f e c t becomes in c r e a s in g l y more d i f f i c u l t beyond 1,200 cps. A pure tone p r e s e n te d a t a v e ry h ig h i n t e n s i t y l e v e l to the a u d ito r y system e s t a b l i s h e s a p a t t e r n of a c o u s tic d i s t o r t i o n c o n ta in in g fre q u e n c ie s which are i n t e g r a l s of the prim ary to n e . (110, p. 131) F u rtherm ore, when the stim u lu s c o n s i s t s o f two to n e s , they i n t e r a c t to produce a d d i t i o n a l to n es whose fre q u e n c ie s a re the sums and d i f f e r e n c e s of the m u ltip le s of the prim ary to n e s . (108, p. 380) By employing an e x p lo rin g tone b e lie v e d to be c lo s e in frequency to one o f the su sp e c te d o v e rto n e s, a b e a tin g e f f e c t i s produced e q u a l in r a t e to the d i f f e r ence between the frequen cy o f the s u b je c tiv e harmonic and the e x p lo r in g to n e . (110, p. 135) I n t h e i r c l a s s i c work on the masking of one pure tone by a n o th e r, Wegel and Lane (104, p. 271) n o ted th e b e a t phenomenon in the 27 frequency re g io n of the masking tone and a l s o , a t f r e q u e n cies which were m u lt i p le s o f th e masking to n e . The b e a ts th ey o b ta in e d th ro ugh the i n t e r a c t i o n o f the o v e r to n es and the e x p lo r in g tone led to t h e i r c o n c lu sio n t h a t harm onics a re produced in the a u d ito r y system by some n o n - l i n e a r c h a r a c t e r i s t i c o f i t s re s p o n s e . Subsequent i n v e s t i g a t i o n s u s in g th e e x p lo r in g tone method o f b e a ts e s t a b l i s h e d the com p lexity o f the d i s t o r t i o n p a t t e r n . (17, 107, 109) This complex o f com bination to n e s was d e m o n stra te d , e x p e rim e n ta lly , to c o n s i s t o f numerous f r e q u e n c i e s . R iesz (79) employed the phenomenon o f b e a ts to * determ ine the d i f f e r e n t i a l s e n s i t i v i t y o f the e a r to i n t e n s i t y . He based h i s ex perim ent on th e o b s e r v a tio n t h a t when one tone i s more in te n s e th an the o t h e r , c a n c e l l a t i o n due to phase o p p o s itio n i s only p a r t i a l . F u r t h e r more, no b e a tin g complex w i l l be d e te c te d u n le s s i n t e r fe re n c e from the weaker tone re a c h e s a c r i t i c a l m inim al v a lu e . He t h e r e f o r e p r e s e n te d the to n a l o u tp u ts of two o s c i l l a t o r s to the s u b j e c t 's e a r so t h a t b e a ts could be e s t a b l i s h e d when the two to n es were ap pro xim ated . He p re s e n te d a tone from one o s c i l l a t o r a t a f ix e d i n t e n s i t y le v e l and th e n g r a d u a lly in c re a s e d the i n t e n s i t y of the o th e r o u tp u t u n t i l a b e a t was observed by the s u b j e c t . By c a l c u l a t i n g th e m inim al and maximal l e v e l n e c e s s a ry fo r the p r o d u c tio n o f t h a t b e a t the i n t e n s i t i v e d i f f e r e n c e 28 limen was e s t a b l i s h e d . D e s c r ip tio n o f Frequency M odulation Stevens and Davis (85, p. 241) su g g e st t h a t b e a ts can be d e s ig n a te d as a s p e c i a l case o f combined am plitude and frequency m odu lation p o s s e s s in g a spectrum of two components. M odulation i s s a id to o ccu r whenever the c h a r a c t e r i s t i c s o f a sound wave are m o d ifie d . Thus, a sound wave i s frequency m odulated when the frequency of the wave i s a l t e r e d in some manner. I f the a l t e r a t i o n i s re p e a te d u n ifo rm ly o r i s p e r i o d i c , th en s i n u s o i d a l f r e quency m odu lation e x i s t s . I f , fo r example, the frequency d i a l of an a u d i o - o s c i l l a t o r p rodu cing a pure tone i s turned back and f o r t h in such a manner as to change th e frequency o u tp u t in a u n ifo rm fa s h io n in r e l a t i o n to tim e, then s i n u s o i d a l frequency m od u latio n of a pure tone i s produced. (163, p. 225) The freq u en cy m odulated tone p o s s e s s e s p a ram eters which a re d e fin e d in the fo llo w in g manner: (40) 1. The C e n tr a l frequency i s d e s c r ib e d as the base frequency around which the m odu lation occurs and r e p r e s e n te d by the symbol [F] 2. The Range whose symbol i s £ A F ] d e s c rib e d as o n e -h a If the t o t a l e x c u rs io n through which th e pure tone i s m odulated. I t i s th e d i s ta n c e in c y c le s p er second betw een the base frequen cy and the d i s t a l l i m i t of the e x c u rs io n . 29 3. The Rate o f m odu lation [f] i s d e fin e d as the t o t a l number o f e x c u rs io n s above and below the c e n t r a l frequ ency t h a t occurs in a s p e c i f i e d u n i t of tim e. 4. The S e n sa tio n l e v e l i s d e fin e d as the number of d e c ib e ls above the norm al th r e s h o ld fo r the m odulated freq u en cy . The frequency m odulated tone can be c o n sid ere d e i t h e r as a co n tin u o u s and s e q u e n t i a l l y v a ry in g tone (85, p. 226) or as a spectrum o f ste a d y tones (39, 113) i n t e r a c t i n g to produce a sound c o n s ta n tly and s e q u e n t i a l l y v a ry in g in freq u en cy . (95, p. 29) The spectrum of a s i n u s o i d a l frequency m odulated pure tone can be o b ta in e d by F o u rie r a n a l y s i s and can be shown m a th e m a tic a lly to c o n ta in a c e n t r a l component and a number o f sid e bands a rra n g e d sy m m etrica lly on e i t h e r sid e of the base f r e quency. (62) The number of s id e bands i s i n f i n i t e . However, the i n t e n s i t y l e v e ls o f the more d i s t a l frequency components of the a c o u s tic spectrum a re v e ry low. T here f o r e , the spectrum can be c o n sid e re d to c o n s i s t of a s p e c i f i c number o f s i g n i f i c a n t sid e bands. (8) The sid e bands a re s e p a r a te d from each o th e r in c y c le s p e r second by an amount e q u a l to th e m o dulatio n r a t e . (62) The m od ulatio n index which i s sometimes r e f e r r e d to as th e d e v i a t i o n r a t i o i s e q u a l to the r a t i o o f the Range to the Rate and i s e x p re sse d as . (53, p. 17) By i t s e l f , th e m o dulatio n index does n o t d i r e c t l y in c r e a s e 30 our u n d e rs ta n d in g of frequency m o d u la tio n . However, when t h i s r a t i o i s a p p lie d to th e a p p ro p r ia te m athem atic t a b l e s th e i n v e s t i g a t o r can o b ta in the number o f s i g n i f i c a n t sid e bands t h a t w i l l be a f f e c t e d by a p a r t i c u l a r v a lu e of the m o d u latio n ind ex . (60, p. 21) In a s i m i l a r manner, the r e l a t i v e am plitu de of each s i g n i f i c a n t sid e band can a ls o be determ in ed from a knowledge o f the m od u latio n index. The spectrum of a 1,000 cps tone which i s s i n u s o i d a l l y m odulated through a range o f 50 cps ( fiv e p e r c e n t o f the c e n t r a l frequ ency) a t a m odulatio n r a t e o f s i x p e r second i s p r e s e n te d in F ig u re 1. In t h i s example, the number of s i g n i f i c a n t sid e bands e q u a ls tw elve on e i t h e r s id e o f the c e n t r a l f r e quency and each i s s e p a r a te d by a d i s ta n c e in c y c le s p er second e q u a l to the r a t e o f m o d u la tio n . Although [ F t A F ] i s e q u a l to tw ice the Range, i t i s to be n o ted t h a t th e re e x i s t sid e bands beyond the e x te n t o f the Range. However, th e s id e band am p litu d es d im in ish r a p i d l y o u ts id e the re g io n [±zsF ] removed from the base freq u en cy . (38, p. 60) In a d d it i o n , the am plitude of th e frequency m odulated sound wave rem ains c o n s ta n t w h ile the frequency v a r i e s s i n u s o i d a l l y around a mean freq u e n cy . (62) S in u s o id a l frequency m odulatio n i s a complex sound p o s s e s s in g c o n s ta n t r e g u la b le a t t r i b u t e s . This stim u lu s u n i t e s in a s i n g l e sound the p r o p e r t i e s o f: (1) com p lexity of spectrum and, (2) c o n s ta n t r e g u la b le A m p litu d e 20 .. 928 952 976 1000 1024 1048 1072 Frequency Fig. 1 . --A c o u stic spectrum o f a 1000 cps w arble tone modulated a t fiv e p er cen t w ith a s i x cycle r a te - -d e v e lo p e d from m odulation index t a b l e s prep ared by K iver. (60, p. 21) 32 ; f re q u e n c ie s and i n t e n s i t y . An a d d i t i o n a l and v a lu a b le c l i n i c a l f e a t u r e o f the frequ ency m odulated pure tone i s i t s r e lu c ta n c e to produce s ta n d in g waves when r e l e a s e d in a t e s t room because no i n t e r f e r e n c e p a t t e r n i s e s t a b l i s h e d . (1, p . 2) S tu d ie s R e la tin g to Frequency M odulation Corso and Lewis (16) d eterm in ed the manner in which l i s t e n e r p r e f e r e n c e s v a r i e d in m u s ic a lly t r a i n e d and u n tr a in e d o b s e rv e rs fo r r a t e and range of frequency m odulated to n e s . A group o f twelve v i b r a t o r to n es were o b ta in e d by combining each of fo u r r a t e s and ran g es of m o d u la tio n . The judgm ents o f v i b r a t o p r e fe r e n c e by the s u b je c ts fo r the e x p e rim e n ta l to n es were arra n g ed in rank o r d e r . M usical a b i l i t y seem ingly had l i t t l e e f f e c t on v i b r a t o p re f e re n c e in which b o th groups dem onstrated an e q u a l choice f o r r a t e s of 6 .0 and 6 .5 c p s. However, the u n t r a i n e d s u b j e c t s i n d ic a te d a p re fe re n c e fo r a range e q u a l to o n e -f o u r th of a m u sic a l s te p w h ile the m u s ic a lly t a l e n t e d fav o red a narro w er range o f o n e - te n th o f a s te p . Youtz and Stevens (113) i n v e s t i g a t e d the component fre q u e n c ie s o f m odulated to n es t h a t could be s e p a r a t e l y i d e n t i f i e d . Hiree to n es were m odulated a t a r a t e o f e ig h t p e r second w ith ran g e s of m o dulatio n d e v ise d so t h a t a c e n t r a l component o f 1,000 cps was e q u a l, tw ice as l a r g e , and h a l f as la rg e as the two accompanying s id e bands. 33 O bservers were i n s t r u c t e d to a d j u s t the frequency o f a pure tone u n t i l i t appeared to e q u a l th e p i t c h o f the m odulated to n e . The i n v e s t i g a t o r s d isc o v e re d t h a t ju d g ments of e q u a l p i t c h showed g r e a t e r v a r i a t i o n as the range o f m o du latio n in c r e a s e d . At the b ro a d e r ra n g e s , the p i t c h of the m odulated frequency becomes le s s i d e n t i f i a b l e . The v e r b a l r e p o r t s of the e x p e rim e n ta l s u b je c ts r e v e a le d t h a t the a p p a re n t p i t c h o f the m odulated tone in e x p lic a b ly s h i f t e d as they probed to match i t w ith a t e s t to n e . The i n v e s t i g a t o r s concluded t h a t in frequency m o du lations of s u f f i c i e n t l y broad range th e component tones a re s a l i e n t enough to be i d e n t i f i e d s e p a r a t e l y . E a rly r e s e a r c h i n v e s t i g a t i n g the d if f e r e n c e limen f o r freq uency used tu n in g fo rk s and plucked s t r i n g s (97) which in tro d u c e d unwanted harm on ics. In an a tte m p t to minimize t r a n s i e n t n o i s e s , (61, p. 95) Shower and Biddulph (83) extended p re v io u s r e s e a r c h by u t i l i z i n g a n o v e l method o f stim u lu s p r e s e n t a t i o n . A r o t a r y a i r condenser was developed to produce a freq u en cy m odulated tone a t a r a t e o f two v a r i a t i o n s p e r second. The o b s e r v a tio n s of fiv e s u b je c ts were s tu d ie d over a range from 31 cps to 11,700 cps a t s e n s a tio n l e v e ls from 5 dB above th r e s h o ld to the l i m i t o f t o l e r a n c e . The a p p a ra tu s p e rm itte d the s u b j e c t to observe a tone of u nv ary in g p i t c h b e fo re the frequ en cy was changed s i n u s o i d a l l y to a new t o n a l v a lu e . The o b se rv e r r e p o r te d when he was a b le to d e t e c t a j u s t 34 n o t ic e a b l e v a r i a t i o n in p i t c h . The i n v e s t i g a t o r s con cluded t h a t a t f r e q u e n c ie s above 500 cps the s m a lle s t p e rc e n ta g e o f frequency change i s ap p ro x im ate ly c o n s ta n t. They a ls o found t h a t below 500 cps the d if f e r e n c e limen becomes c o n s ta n t w ith freq uency u n t i l the very low to n es a re re a c h e d . Groen and V e rs te ig h (40) i n v e s t i g a t e d the frequency a n a ly z in g a b i l i t y of th e human e a r in which a s i n u s o i d a l frequency m odulated tone was the s tim u lu s . W ithout d i s c l o s i n g the a t t r i b u t e s or number o f t h e i r e x p e rim e n ta l s u b j e c t s the a u th o rs h e ld c o n s ta n t the c e n t r a l frequency o f the m odulated tone and i t s s e n s a tio n l e v e l w hile they v a rie d e i t h e r the range or the r a t e o f m odula t i o n . In t h i s manner the t r a n s i t i o n p o in t betw een a pure tone and a m odulated tone was e s t a b l i s h e d fo r o c ta v e s from 250 to 4,000 cp s. From t h e i r d a ta , the a u th o rs make the fo llo w in g c o n c lu s io n s : 1. The c r i t i c a l band w id th c o rresp o n d s to t h a t p a r t o f the Organ o f C o r ti in which one pure tone i s p e rc e iv e d . 2. The phenomenon o f masking i s produced by o th e r v i b r a t i o n s t h a t a c t upon t h i s c r i t i c a l band. 3. The c r i t i c a l band i s the l i m i t of the e a r ' s c a p a c ity f o r sim ultan eo u s frequency a n a l y s i s o f a complex sound. The e a r i s 35 n o t a b le to perfo rm a frequency a n a ly s is i f the d i f f e r e n c e between two or more harm onic v i b r a t i o n s p re s e n te d sim u lta n e o u s ly i s s m a lle r th an th e c r i t i c a l band w id th . 4. Tones p r e s e n te d to th e system t h a t a c t i v a t e sen sory a re a s w ith in the c r i t i c a l band w id th produce a m echanical i n t e r a c t i o n r e s u l t i n g in the p e rc e p tio n o f b e a t s . 5. A m odu lation r a t e o f 3 c y c le s p e r second i s the d if f e r e n c e limen f o r frequen cy . W ebster (102, 103) d e v is e d a group h e a rin g t e s t t h a t employed a w arbled tone w ith a r a t e o f 5 c y c le s p e r second and a range of 12.5 p e r c e n t o f th e base frequ ency. The t e s t s t i m u l i were re c o rd e d on phonograph d i s c s in groups o f zero to fo u r p u l s e s . Each p u lse w ith in an item was l e s s in te n s e th an the p re c e d in g p r e s e n t a t i o n . The t e s t was p r e s e n te d to 200 e x p e rim e n ta l p e rs o n n e l under two c o n d itio n s . Under the f i r s t c o n d itio n , the t e s t item s were g e n e ra te d i n t o a r e v e r b e r a n t room thro u g h a m u ltip le a r r a y o f lo u d sp e a k e rs. In a second l i s t e n i n g c o n d itio n , the s t i m u l i were p r e s e n te d b i n a u r a l l y over t h i r t y - s i x matched p a i r s o f earp h o n es. A h ig h degree o f c o r r e l a t i o n was d e m o n strated between the two p r e s e n t a t i o n s . R e i l l y (77) r e p o r t s th e use of w arble tone s t i m u l i of u n s t a te d r a t e and range to d eterm ine the a u d ito ry t h r e s h o ld s o f i n f a n t s and c h il d r e n . The to n es were 36 g e n e ra te d thro u g h two lo u d sp e ak e rs p la c e d to the r i g h t and l e f t o f the s u b je c t who was s e a te d in a "sound p ro o fed " room. The a u d ito r y th r e s h o ld was determ ined by in c r e a s in g the i n t e n s i t y o f the stim u lu s in 20 dB s te p s f o r each base frequency as the i n v e s t i g a t o r observed th e r e a c t i o n s of the s u b j e c t to the to n e s . In o b ta in in g pure tone a u d io grams u sin g the same pro ced u re the i n v e s t i g a t o r n o ted a d isc re p a n c y in th r e s h o ld v a lu e s in which the s u b je c t r e s ponded to w arble tones a t a lower s e n s a tio n l e v e l th an to pure to n es f o r the same b ase frequ ency. R e il l y c a l l s fo r a more thorough com parison o f the two s t i m u l i , b u t t e n t a t i v e l y concludes t h a t the th r e s h o ld d i f f e r e n c e s are m ediated a t or n e a r the c o r t i c a l l e v e l . The a u th o r gave no a t t e n t i o n , however, to the development of s ta n d in g waves by pure to n es g e n e ra te d i n t o a sound f i e l d . CHAPTER I I I SUBJECTS, MATERIALS, EXPERIMENTAL, AND STATISTICAL PROCEDURES E x p erim en tal Design A c e l l diagram of th e experim ent i s shown in F igure 2. The th r e e v a r i a b l e s ; (1) C o n d itio n s, (2) Sub j e c t s , and (3) S tim u li a re shown in th re e dim ensions su b d iv id ed in to t h e i r r e s p e c t iv e components. Reading the c e n te r p o r t i o n of the i l l u s t r a t i o n from l e f t to r i g h t are the groups in to which the s u b j e c t s were c l a s s i f i e d a c c o rd ing to h e a rin g a c u i t y : (1) Normal, (2) C onductive, (3) S e n s o ry -n e u ra l. The o to - p a th o lo g ic s u b je c ts were f u r t h e r d iv id e d i n t o groups acc o rd in g to degree o f h e a rin g impairm ent and c l a s s i f i e d a s: (1) Moderate l o s s , (2) Severe l o s s . To the r i g h t o f the diagram are p r e s e n te d the th r e e s t i m u l i : (1) Pure to n es (PT ), (2) Warble tones (WT), (3) Speech (Sp). To the l e f t of the diagram are the e x p e rim e n ta l c o n d itio n s : (1) Sound f i e l d (SF), (2) E a r phones (Phone). These c o n d itio n s a re f u r t h e r su b d iv id ed in to (1) R igh t e a r (R t), (2) L e ft e a r (L t) , (3) B in a u ra l (B in). I t i s seen t h a t each s u b je c t was g iven th re e d i f f e r e n t s t i m u l i under two c o n d itio n s o f s t i m u l i p r e s e n t a t i o n . However, pure tone s t i m u l i were n o t p re s e n te d in a sound f i e l d . In a d d i t i o n , h a r d - o f - h e a r in g s u b je c ts were 37 CONDITION 4J Moderate Severe Severe Moderate Normal Conductive S e n so ry -n e u ral SUBJECTS F ig . 2 . - - C e l l diagram of the e x p erim e n tal design u> o o 39 g iv e n a q u e s tio n n a ir e r e l a t i v e to the s u b j e c t iv e a s p e c ts o f t i n n i t u s . S u b je c ts Norma 1 s u b j e c t s . A group o f tw enty s u b j e c t s w ith norm al h e a rin g (Group I ) was s e l e c t e d from the p e rs o n n e l employed by the O to lo g ic M edical Group, an a s s o c i a t i o n o f f iv e p h y s ic ia n s who conduct a p r a c t i c e lim ite d to the stu d y o f the e a r in Los A ngeles, C a l i f o r n i a . When o f f i c e a c t i v i t y p e rm itte d the rem oval o f any employee from h i s d u t i e s , he was c a l l e d upon as a s u b j e c t . The i n v e s t i g a t o r was employed by the "Group,t as a C l i n i c a l A u d io lo g is t. Every member o f the norm al group was female and ranged in age from n in e te e n to f o r t y - s i x w ith a mean age o f 26.6 y e a r s . A lthough d i f f e r e n c e s are shown to e x i s t betw een median th r e s h o ld v a lu e s o f norm al h e a rin g males and fem ales (70, p. 34) the problem i s b ased on a com pari son o f i n d i v i d u a l re s p o n se s to s e l e c te d s t i m u l i and n o t o f a b s o lu te t h r e s h o ld s . T h e re fo re , i t was assumed t h a t the s e l e c t i o n o f an a l l female norm al h e a rin g p o p u la tio n would n o t u n re a so n a b ly in f lu e n c e the r e s u l t s . The pure tone a i r co n d u ctio n audiogram s by which the norm al h e a rin g s u b j e c t s were s e l e c t e d may be seen in Appendix I . H a rd -o f-h e a rin g s u b j e c t s . A group of s i x t y h a rd - o f - h e a r in g s u b je c ts was o b ta in e d from p a t i e n t s v i s i t i n g th e m ed ica l o f f i c e s of the Group fo r d i a g n o s ti c and 40 r e h a b i l i t a t i v e c o n s u l t a t i o n . Each h a r d - o f - h e a r in g s u b je c t had had a t l e a s t one a u d io m e tric stud y p r i o r to h i s p a r t i c i p a t i o n i n the experim en t and had been seen by one o f the O to l o g is ts fo r e x am in a tio n . In o rd e r to i n v e s t i g a t e th e c o n t r i b u t i o n o f p a th o logy to any observed d i f f e r e n c e s in th r e s h o ld v a lu e s , the h a r d - o f - h e a r in g s u b je c ts were s e p a r a te d i n t o two groups under the fo llo w in g h e a d in g s: 1. Conductive h e a r in g l o s s . 2. S e n so ry -n e u ra l h e a rin g l o s s . In an e f f o r t to e v a lu a te the in flu e n c e o f a u d ito ry th r e s h o ld l e v e l on any observed d i f f e r e n c e s in resp o n se s o f the s u b je c t to the s t i m u l i , the two h a r d - o f - h e a r in g sub-groups were f u r t h e r c o n sid e re d in term s of the e x te n t of lo s s measured in d e c i b e l s . Each o f the h a r d - o f - h e a r in g s u b j e c t s was a ssig n e d to e i t h e r one or two groups a c c o rd ing to the h e a rin g l e v e l of h i s pure tone audiogram. These two c l a s s i f i c a t i o n s were: 1. Moderate h e a r in g l o s s . 2. Severe h e a r in g l o s s . Table 1 shows d i s t r i b u t i o n of the s u b je c ts a c c o rd ing to im pairm ent. The pure tone a i r co n d u ctio n and bone co nduction audiograms by which the h a r d - o f - h e a r in g s u b je c ts were s e l e c te d may be seen in Appendix I . The h a rd - o f - h e a r i n g e x p e rim e n ta l p o p u la tio n was TABLE 1 41 DISTRIBUTION OF EXPERIMENTAL POPULATION ACCORDING TO CLASSIFICATION OF HEARING ACUITY Degree of Loss Type of Loss Norma1 Conductive Sensory- N eura1 T o ta l Norma 1 20 20 Moderate 15 15 30 Severe 15 15 30 T o ta l 20 30 30 80 f u r t h e r d iv id e d i n t o fo u r sub-groups each c o n s i s t in g of f i f t e e n members. These groups were l a b e ll e d Group I I , I I I , IV, and V r e s p e c t i v e l y . Group I I (Moderate co n d u ctiv e l o s s ) . This group was composed o f seven males and e i g h t fem ales. The males ranged in age from t h i r t y - o n e y e a rs to f i f t y y e a rs w ith a mean age of fo rty -tw o y e a r s . The fem ales ranged in age from t h i r t y - o n e to f i f t y - f o u r y e a rs w ith a mean age of 45 .5 y e a r s . Group I I I (Severe co n ductiv e l o s s ) . This group c o n s is te d o f s i x m ales and n in e fem a le s. The males ranged in age from f i f t y y e a rs to s i x t y - f i v e y e a rs w ith a mean age of 61.6 y e a r s . The fem ales ranged in age from f i f t y - 42 one y e a rs to sev en ty y e a rs w ith a mean age o f 58.8 y e a r s . Group IV (Moderate s e n s o r y - n e u r a l l o s s ) . This group was composed o f e ig h t m ales and seven fem a le s. The m ales ranged in age from t h i r t y - t w o y e a rs to sev en ty y e a rs w ith an average age o f 52.1 y e a r s . The fem ales ranged in age from tw e n ty - s ix y e a rs to s ix ty - s e v e n y e a rs w ith an average age o f 50.7 y e a r s . Group V (Severe s e n s o r y - n e u r a l l o s s ) . This group was composed o f te n m ales and f iv e fem ales. The m ales ranged in age from tw e n ty -fiv e y e a rs to s ix ty - s e v e n y e a rs w ith a mean age of 49.7 y e a r s . The fem ales ranged in age from tw enty y e a rs to s i x t y - f i v e y e a rs w ith an average age of f o r t y - n i n e y e a r s . Table 2 shows the d i s t r i b u t i o n o f th e h a r d - o f - h e a rin g s u b j e c t s a cc o rd in g to m ed ica l d ia g n o s e s . T ables 3 and 4 show the d i s t r i b u t i o n s o f the normal and h a r d - o f - h e a r i n g s u b j e c t s a c c o rd in g to age and sex. N on-audiom etric c r i t e r i a . I t was reaso n ed t h a t c o n d itio n s o th e r th an the n a tu r e of th e s t i m u l i m ight con t r i b u t e to v a r i a t i o n s in a u d io m e tric th r e s h o ld s thus producing s p u rio u s r e s u l t s in th e e x p e rim e n ta l d a ta . I t was assumed t h a t th e c o n d itio n s l i s t e d below could a f f e c t a u d io m e tric s c o r e s . T h e re fo re , any c a n d id a te under consid e r a t i o n as a s u b je c t in th e experim en t was d i s q u a l i f i e d i f he f e l l under one o f the fo llo w in g c a t e g o r i e s : 1. Worked in h ig h i n t e n s i t y n o is e . 43 TABLE 2 DISTRIBUTION OF MEDICAL DIAGNOSES OF THE HARD-OF-HEARING SUBJECTS D iagnosis H a rd -o f-h e a rin g Sub-group T o ta l I I I I I IV V Conductive O to s c le r o s is 13 15 28 O t i t i s Media 2 2 S e n so ry -n e u ra l H e re d ita ry 12 12 24 V ascular 2 2 P re sb y c u sis 1 1 Toxic 2 1 3 T o ta l 15 15 15 15 60 2. Suspected of f u n c tio n a l h e a r in g l o s s . 3. Engaged in l e g a l a c tio n in which h e a rin g im pairm ent was a q u e s tio n . 4. Did n o t speak E n g lis h . 5. Diagnosed upper r e s p i r a t o r y i n f e c t i o n . 6. Diagnosed a c t iv e su p p u ra tiv e o t i t i s media. 7. Complained o f e a ra c h e . 8. Diagnosed blockage o f E u sta c h ia n tu b e . 9. Paper p a tc h over p e r f o r a te d tympanic 44 membrane. 10. Was undergoing v a s o d i l a t o r th e ra p y f o r M e n ie re 's syndrome and r e l a t e d d i s o r d e r s . 11. Complained o f f a t i g u e . 12. D isp lay ed r e lu c ta n c e to engage in the t e s t . TABLE 3 DISTRIBUTION OF NORMAL HEARING AND HARD-OF- HEARING SUBJECTS ACCORDING TO AGE Age (Y ears) Norma 1 H earing S u b je c ts (Group I ) H a rd -o f-h e a rin g Sub -group T o ta l I I I I I IV V 16-20 3 1 4 21-25 8 1 9 26-30 5 1 1 7 31-35 3 4 1 1 9 36-40 1 1 2 41-45 4 2 2 8 46-50 1 2 1 1 1 6 51-55 3 3 4 10 56-60 1 1 4 6 61-65 2 9 1 12 66-70 3 1 3 7 T o ta l 20 15 15 15 15 80 Mean Age 26.6 43.8 51.4 60.0 49.3 46.2 Equipment The experim ent was conducted in two a d jo in in g a c o u s t i c a l l y i s o l a t e d rooms p r e f a b r i c a t e d by the I n d u s t r i a l A c o u stic s Company. These e n c lo s u re s were lo c a te d in the 45 o f f i c e o f th e O to lo g ic M edical Group. The in s id e dimen s io n s o f each room were e i g h t f e e t long by s i x f e e t , e ig h t in ch es wide by s i x f e e t , s i x inches h ig h . A c o n n ectin g window p e rm itte d o b s e r v a tio n o f the s u b j e c t . One room in which the s u b j e c t was s e a te d was d e s ig n a te d as th e T est Room and the o th e r the C o n tro l Room. TABLE 4 DISTRIBUTION OF NORMAL HEARING AND HARD-OF- HEARING SUBJECTS ACCORDING TO SEX Sex Norma 1 H earing S u b je c ts (Group I) H a rd -o f-h e a rin g Sub -group T o ta l I I I I I IV V Male 0 7 8 6 10 31 Fema le 20 8 7 9 5 49 T o ta l 20 15 15 15 15 80 A B elton e model 15A two chann el pure tone and speech audiom eter p ro v id ed th e measured s tim u lu s . Pure to n es were m odulated w ith an A llis o n Warble Tone A dapter model 101 plugged i n t o th e B eltone c o n so le . The a d a p te r produced a to n a l complex t h a t e x ec u te d s i x o s c i l l a t i o n s each second th ro u g h a frequen cy range e q u iv a le n t to fiv e p e r c e n t of the m odulated t o n e . The c a l i b r a t e d phonograph re c o rd s (CID A uditory T e sts W--1 A and B) were p lay ed on a Rek-0-Kut Rondine, J r , 46 * model L --3 7 , two speed t u r n t a b l e u t i l i z i n g a ceram ic h ig h impedance p ic k -u p . Live v o ice i n s t r u c t i o n s to th e s u b je c t were fed throug h an E le c tro -V o ic e model 926 c r y s t a l m ic ro phone. The tw o-channel equipm ent p e rm itte d d e li v e r y of the s e l e c t e d s tim u lu s a t d e s ig n a te d s e n s a tio n l e v e ls in to the t e s t room e i t h e r through T elephonic TDX--39 earphones equipped w ith MX--41--AR cush ion s o r through an E le c t r o - Voice model SP--12B lo ud sp eak er housed in an A c o u stiC ra ft fo ld e d horn e n c lo s u re . A " ta lk - b a c k " communication system employed an E le c tro -V o ic e model 615 microphone to a moni t o r head s e t in the C o n tro l Room. A b lo ck diagram o f the e x p e rim e n ta l equipm ent i s p r e s e n te d in F ig u re 3. A d d itio n a l m a t e r i a l used in the experim ent i s p r e se n te d below. 1. Forms A, B, C, D, E, and F f o r re c o rd in g d a ta . (See Appendix VI) 2. L i s t s of spondaic words in the sequence p r e s e n te d on CID t r a n s c r i p t i o n s . (See Appendix V II) 3. Otoscope and sp e c u la . E x p erim en tal Procedure P re lim in a ry i n v e s t i g a t i o n re v e a le d t h a t the c o l l e c t i o n o f e x p e rim e n ta l d a ta from each s u b je c t would take a p p ro x im ately f o r t y - f i v e m in u te s. As the d a il y a u d io lo g i- c a l work load of the o f f i c e was d i f f i c u l t to p r e d i c t , no 47 * p P a t i e n t S ig n a l o------ Earphones Loudspeaker S u b j e c t ' s Microphone TEST ROOM Warble Tone Adapter Audiometer T u rn ta b le r “ U-i E xperim enter ' s Microphone Microphone and Ta lk-back A m p lifie rs Ta lk -b ack Loudspeaker HP Earphone CONTROL ROOM F ig . 3 . --D iagram o f the e x p e rim e n ta l equipment appointm ent was made w ith the s u b j e c t . The u s u a l o f f i c e r o u tin e c a l l e d f o r each p a t i e n t to be seen f i r s t by the Audiology Departm ent in o rd e r to o b ta in a pure tone a i r co nductio n and bone co ndu ction audiogram . A d d itio n a l a u d io m e tric s t u d i e s such as a speech r e c e p t i o n th r e s h o ld , d i s c r im i n a t io n s c o re , a p p ro p r ia te r e c r u itm e n t t e s t or m a lin g e rin g t e s t s were o b ta in e d by the a u d io l o g i s t when e v e r he b e lie v e d the sc o re s would be of v alue to the o t o l o g i s t i n e s t a b l i s h i n g the d ia g n o s is . Then the p a t i e n t c o n s u lte d the p h y s ic ia n w ith whom he had an appointm ent. 4 8 O c c a s io n a lly , the o t o l o g i s t would r e f e r th e p a t i e n t to the a u d i o l o g i s t f o r f u r t h e r t e s t i n g . T h e re fo re , d u rin g the d a i l y a c t i v i t i e s o f th e o f f i c e , th e e x p e rim e n te r had o cca s io n to c o n s id e r a number o f p a t i e n t s as s u b j e c t s fo r the stu d y . P a t i e n t s became c a n d id a te s as s u b je c ts in the exp erim ent i f adequate time p e rm itte d the c o l l e c t i o n of d a ta in one s i t t i n g and i f t h i s c o l l e c t i o n d id n o t i n t e r f e r e w ith the norm al r o u t in e o f the o f f i c e . A fte r d e te rm in in g the a v a i l a b i l i t y o f the t e s t equipm ent, the a u d io m e tric re c o r d s of the p a t i e n t were examined to a s c e r t a i n the type and degree o f h e a rin g lo s s . I f the c a n d id a te was found to s a t i s f y the re q u ire m e n ts of one of the h a r d - o f - h e a r in g gro u p s, h i s h i s t o r y was s c r u t i n iz e d to determ in e f u r t h e r the p resen c e o f any l im i ti n g f a c t o r s to q u a l i f i c a t i o n as a s u b j e c t . An o to sc o p ic exam in atio n of the e a r c a n a l by the a u d i o l o g i s t then follow ed to a s s e s s the p a ten cy o f the c a n a l. C ustom arily, the a u d i o l o g i s t would c h a t b r i e f l y w ith th e p a t i e n t p r i o r to the t e s t . This o p p o r tu n ity was used to determ ine w hether the p a t i e n t had a " c o l d , '1 s u f f i c i e n t command of the E n g lis h language to u n d e rs ta n d i n s t r u c t i o n s , or any a d d i t i o n a l d i s q u a l i f y i n g c o n d itio n s . A ll the a p p ro p ria te re q u ire m e n ts f o r s e l e c t i o n of a s u b je c t were a ls o a p p lie d to th e n orm ally h e a rin g group. I f a c a n d id a te s a t i s f i e d the c r i t e r i a fo r s e l e c t i o n he was assumed to be a p o t e n t i a l s u b j e c t . 49 C a li b r a t i o n o f t e s t e q u ip m en t. The equipm ent u t i l i z e d in t h i s ex perim en t was r o u t i n e l y c a l i b r a t e d e v ery th r e e months by a r e p u ta b le a c o u s t i c a l e n g in e e rin g firm . The e s t a b l i s h e d p ro cedure o f the Audiology S e c tio n of the O to lo g ic M edical Group demanded t h a t any unex pected t h r e s h o ld s h i f t u sin g any of the audiom eters in the dep artm ent was to be c o rro b o ra te d by a r e t e s t u sin g a n o th e r i n s t r u m ent. Since the t e s t equipm ent i s in c o n s ta n t use throug h ou t o f f i c e hours n o t much time would e la p s e b e fo re an o p in io n re g a rd in g the r e l i a b i l i t y o f an audiom eter was e s t a b l i s h e d . At no time were d a ta c o l l e c t e d fo r t h i s experim ent when the a u d io m e te r's c a l i b r a t i o n was s u s p e c t. Sequence of s t i m u l i p r e s e n t a t i o n . In o rd e r to reduce e r r o r s a r i s i n g from sequence o f p r e s e n t a t i o n , the s t i m u l i (warble to n e , pure to n e , and rec o rd ed spondaic words) and the c o n d itio n s of p r e s e n t a t i o n (earphones and s o u n d fie ld ) were random ized. This was accom plished fo r each s u b je c t by draw ing a s l i p of paper from a c o n ta in e r on which had been w r i t t e n a code number d e s ig n a tin g each of the p o s s ib le com binations of the fo llo w in g fiv e sub t e s t s com prising the exp erim en t: (78, p. 370) A. P r e s e n t a t io n of pure to n es by earp h o n es. B. P r e s e n t a t io n of w arble to n es by earp h o n es. C. P r e s e n t a t io n of w arble to n es by sound f i e l d . D. P r e s e n t a t i o n of re c o rd e d spondaic words by e a rp h o n e s . 50 E. P r e s e n t a t io n o f re c o rd e d spondaic words by so u n d fie Id. For example, the above sequence, item s A thro u g h E o f s u b - t e s t p r e s e n t a t i o n s m ight be d e s ig n a te d as p r e s e n t a t i o n " l 1 1 w h ile the r e v e r s e o r d e r, E, D, C, B, A d e s ig n a te d as p r e s e n t a t i o n "2 ". Each of the forms, on which the e x p e rim e n ta l d a ta were re c o rd e d (see A, B, C, D, and E in Appendix VI) was p la c e d on mimeographed 3" x 5" b lan k index c a r d s . Before c o l l e c t i n g the d a ta a number was drawn f o r each s u b je c t and a pack o f fiv e cards was arran g ed in the sequence c o rresp o n d in g to t h a t number. These card s were s ta p le d to g e th e r and in the o rd e r of drawing p la c e d in a c o n ta in e r fo r easy a c c e s s i b i l i t y . When the d a ta were to be c o l l e c t e d , the f i r s t pack of cards was drawn from the c o n ta in e r . The arrangem ent of th ese card s determ ined the p r e s e n t a t i o n sequence. In a l l odd numbered s u b je c ts the r i g h t e a r was t e s t e d f i r s t . A ll even numbered s u b je c ts had t h e i r l e f t e a r t e s t e d f i r s t . At the b e g in n in g of each t e s t a mimeographed m aste r card (see form F in Appendix VI) was completed by e n te r in g in fo rm a tio n from the p a t i e n t ' s o f f i c e c h a r t as to : (1) name, (2) age, (3) d ia g n o s is , (4) d a te and (5) sequence num ber. The t o t a l d a ta c o l l e c t i n g p ro c e ss took tw enty-one months to com plete. I n s t r u c t i o n s to the s u b j e c t . The s u b je c t was led 51 i n t o the t e s t room and s e a te d in a c o m fo rtab le c h a ir facin g the lo u d sp e a k e r. The f r o n t leg s of the s u b j e c t 's c h a ir r e s t e d on a f l o o r mark s i x f e e t from th e leg s o f the lo ud sp eak er e n c lo s u r e . While the e x p e rim e n te r was s e a t i n g th e s u b je c t the fo llo w in g i n tr o d u c ti o n was m ade: "Good morning (or a fte rn o o n ) my name i s R ichard Hughes. I am one o f th e a u d io - l o g i s t s and I am going to t e s t your h e a r in g . I am going to t e l l you e x a c tly what to do from th e o th e r room where I w i l l be d u rin g the t e s t . " I f th e s u b j e c t 's h e a r in g lo ss was of such a degree as n o t to p e rm it him to h e a r the i n tr o d u c ti o n , the g re e tin g was d e li v e r e d under a p p ro p r ia te a m p l i f i c a t i o n . Depending upon which s u b - t e s t was randomly s e l e c te d f o r the f i r s t s tim u lu s p r e s e n t a t i o n , the i n tr o d u c ti o n and i n s t r u c t i o n s were p r e s e n te d by e i t h e r earphones or lo u d sp e ak e r. Again, depending upon which stim u lu s was introduced to the s u b j e c t d u rin g th e experim ent the a p p ro p ria te i n s t r u c t i o n s were o f f e r e d from the fo llo w in g : A. For Pure to n es and Warble to n e s . "You a re going to h e a r a s e r i e s of to n e s . Each tim e you h e a r a to n e , no m a tte r how loud o r f a i n t i t may sound, p r e s s down on the b u tto n I have g iv en you. Hold the b u tto n down as long as you h e a r the to n e . In o th e r w ords, when you no lo n g er h e a r the tone r e l e a s e the b u tto n . Do you have any q u e s tio n s ? " B. For Recorded spondee words. "You a re going to h e a r a s e r i e s of two 52 s y l l a b l e words l ik e 'a r m c h a i r ,' 'o u t l a w ,' and 'd a y d re a m .' P le ase say each word as you h e a r i t . I f you cannot u n d e rs ta n d a word p le a s e rem ain s i l e n t . However, you may make a guess i f you w ish . Do you have any q u e s tio n s ? " The p re c e d in g i n s t r u c t i o n s were memorized by the e x p e rim e n te r and d e liv e r e d to each s u b j e c t a t the a p p ro p r i a t e time d u rin g th e e x p erim en t. O b tain in g the to n a l th r e s h o ld v a l u e . The fo llo w ing p ro cedu re was employed in the d e te r m in a tio n of pure tone and w arble tone h e a r in g th r e s h o ld s . The t e s t began w ith the p r e s e n t a t i o n o f 1,000 cps to n e . A to n e , about two to th r e e seconds in d u r a tio n was p r e s e n te d to the e a r under t e s t a t a l e v e l which was presumed to be a p p ro x im ately 25 dB above the th r e s h o ld fo r the freq u en cy . I f the tone was n o t h eard the i n t e n s i t y l e v e l was in c r e a s e d a p p r o p r i a te ly u n t i l the s u b je c t c o r r e c t l y respon ded. Then, in decrem ents of 10 dB s te p s the i n t e n s i t y l e v e l was a tte n u a te d u n t i l the s u b je c t no lo n g er responded to the s tim u lu s . The s i l e n t i n t e r v a l between stim u lu s p r e s e n t a t i o n s was a t l e a s t th r e e second s. At t h i s j u n c t u r e , the i n t e n s i t y le v e l was r e tu r n e d to t h a t p o in t where the s u b j e c t l a s t responded and th e tone was p re s e n te d tw ice to o b ta in a t l e a s t a tw o - o u t- o f- f o u r re s p o n s e . The i n t e n s i t y was then reduced in f iv e d e c i b e l s te p s making two or th r e e p r e s e n t a t i o n s o f th e s i g n a l in o rd e r to o b ta in the 50 p e r cen t resp o n se c r i t e r i o n a t each 53 i i n t e n s i t y l e v e l . Thus, the descen din g t h r e s h o ld was d eterm in ed . This was the m inim al i n t e n s i t y l e v e l a t which the s u b je c t c o r r e c t l y responded to 50 p e r c e n t of th e to n al p r e s e n t a t i o n s which had been p r e s e n te d in b u r s t s o f two to th r e e se co n d s' d u r a tio n a t d e c re a s in g m agnitudes com mencing a t a l e v e l above the re c o rd e d th r e s h o ld . Next, s t a r t i n g a t a le v e l below the re c o rd e d d escend ing t h r e s ho ld where the s i g n a l g ained no resp o n se from the s u b j e c t on th re e p r e s e n t a t i o n s , the i n t e n s i t y was in c re a s e d by fiv e d e c ib e l s te p s u n t i l a 50 p e r c e n t c o r r e c t resp o n se was o b ta in e d . This v alue was the ascending th r e s h o ld . In th o se cases where the descending and ascend ing th r e s h o ld s were n o t i d e n t i c a l the two r e a d in g s were re c o rd e d and the average o f the two v a lu e s were d e s ig n a te d as the th r e s h o ld f o r t h a t freq u en cy . The th r e s h o ld fo r each su c c e e d in g ly h ig h e r o ctave frequency to be a s s e s s e d was d eterm ined in the same manner as o u tlin e d above u n t i l a th r e s h o ld v a lu e fo r the 4,000 cps tone was o b ta in e d . The th r e s h o ld s f o r 500 cps and 250 cps were th en o b ta in e d in t h a t o r d e r. As Brown (9) concluded t h a t no s i g n i f i c a n t improve ment o c cu rred on the second t e s t f o r any o f the t e s t fre q u e n c ie s and t h a t the p r a c t i c e e f f e c t does n o t in flu e n c e a second pure tone m easurement, only one t e s t was performed on each s u b j e c t . In a s i m i l a r i n v e s t i g a t i o n , Burns and H in c h lif f e (12) found a one to two d e c ib e ls improvement of th e h e a rin g th re s h o ld on the second pure tone t e s t and 54 concluded t h a t the d i f f e r e n c e was of l i t t l e c l i n i c a l s i g n i f i c a n c e . O btaining th e speech r e c e p t i o n t h r e s h o l d . P ro c e d u re s f o r the e s ta b lis h m e n t of pure tone a u d ito ry t h r e s h o ld s (even though c h a r a c t e r i z e d by lack of agreem ent) a re r e l a t i v e l y abundant in the l i t e r a t u r e as compared to the number of p u b lis h e d te c h n iq u e s f o r the e s ta b lis h m e n t o f speech r e c e p t i o n t h r e s h o ld s . (15; 72, p . 119) T h e re fo re , i t was n e c e s s a ry to d e v ise a re a so n a b le a u d io m etric tec h n iq u e f o r the e s ta b lis h m e n t o f the speech r e c e p t i o n t h r e s h o ld . One o f th e b a s i c re q u ire m e n ts was to p re p a re a method s u f f i c i e n t l y i d e n t i c a l to the t o n a l th re s h o ld tec h n iq u e in o rd e r to reduce the p o s s ib le e f f e c t o f measure ment procedure on the r e l a t i o n s h i p among pure to n e , w arble to n e , and speech t h r e s h o ld s . The fo llo w in g method was employed to e s t a b l i s h the speech r e c e p t i o n th r e s h o ld u sin g re c o rd e d spondaic word l i s t s W--1A and B. The t r a n s c r i p t i o n was p la c e d on the t u r n t a b l e and the motor and a m p lif ie r tu rn ed on and allow ed to warm up _ s- fo r a b r i e f p e r io d . The a p p ro p r ia te speed of r o t a t i o n was s e l e c t e d which in t h i s case was 33-1/3 r .p .m . The 1,000 cps c a l i b r a t i o n tone was s e t to zero r e f e r e n c e l e v e l by a d ju s ti n g the V.U. m eter of the au dio m eter. Blocks o f fo u r words each were p re s e n te d to the e a r under t e s t a t a l e v e l b e lie v e d to be about 25 dB above t h r e s h o ld . I f a l l 55 the words f i r s t p r e s e n te d a t t h i s l e v e l were n o t id e n tifie d ! c o r r e c t l y th en th e i n t e n s i t y in c r e a s e d a p p r o p r i a t e l y . Using b lo c k s of fo u r words each, th e i n t e n s i t y l e v e l was a tte n u a te d in 10 dB s te p s fo r each b lo ck u n t i l th e s u b je c t r e p e a te d i n c o r r e c t l y a t l e a s t th re e o f the fo u r word s e g m ent. At t h i s p o in t the i n t e n s i t y was r e tu r n e d to th e l e v e l where the o b se rv e r l a s t responded c o r r e c t l y to the e n t i r e b lock o f w ords. The i n t e n s i t y was then red uced in 5 dB s te p s u n t i l a l e v e l was rea ch ed where the s u b j e c t responded c o r r e c t l y to two of th e fo u r word s t i m u l i . Hie descending th r e s h o ld was o b ta in e d in t h i s manner. I h i s p o in t on the i n t e n s i t y s c a le was b e lie v e d to be th e m in i mal v a lu e a t which the s u b j e c t responded c o r r e c t l y to 50 p er c e n t o f the spondee word s t i m u l i . Next, b eg in n in g a t a p o in t w e ll below the rec o rd ed d escend ing th r e s h o ld , the i n t e n s i t y was in c re a s e d in 5 dB s te p s u n t i l a l e v e l was reached where the s u b je c t responded to two o f the fo u r words in the b lo c k . This v a lu e was judged to be the ascending th r e s h o ld . In the case where a s u b j e c t responded to only one word o u t of fo u r and th en to th r e e o u t of fou r a t the n e x t p r e s e n t a t i o n le v e l the v a lu e a t which he i d e n t i f i e d the g r e a t e r number o f words was tak en as t h r e s h o ld . I f the ascend ing and descend ing t h r e s h o ld s were n o t i d e n t i c a l the average of the two v a lu e s was re c o rd e d as the a u d ito r y th r e s h o ld f o r rec o rd ed spondee w ords. A sim ple b u t im p o rta n t com putation had to be done however 56 b e fo re the f i n a l r e c o r d in g of the a u d ito r y speech t h r e s h o ld . Ten dB were s u b t r a c t e d from th e th r e s h o ld l e v e l in d ic a t e d on the h e a rin g lo s s d i a l o f the aud io m eter. This a r i t h m e t ic i s perform ed b ecause the c a l i b r a t i o n tone and the c a r r i e r p h rase p re c e d in g each word stim u lu s i s re c o rd e d e x a c tl y 10 dB above the spondee word. Omission o f t h i s com putation would o f f e r v a lu e s 10 dB p o o re r th an the a c t u a l i n t e n s i t y of the words a t th r e s h o ld l e v e l . In the f i n a l a n a l y s i s , the p ro c e d u re s f o r th e d e te r m in a tio n of t h r e s h o ld s f o r to n a l s t i m u l i and fo r re c o rd e d spondee words were d e v ise d in o rd e r to s a t i s f y the fo llo w in g re q u ire m e n ts : 1. To r e f l e c t the c l a s s i c a l p a t t e r n of the method of l i m i t s . 2. To be re a s o n a b ly u n ifo rm and sim ple in the method o f stim u lu s p r e s e n t a t i o n . 3. To be s u f f i c i e n t l y i d e n t i c a l i n stim u lu s p r e s e n t a t i o n . 4. To p e rm it e asy r e p e t i t i o n o f th e experim ent by a n o th e r i n v e s t i g a t o r . Q u e s t i o n n a i r e . The f i n a l s te p in the e x p e rim e n ta l d e s ig n was th e com pletio n of a s h o r t , one-page q u e s t io n n a i r e by each s u b j e c t . (See Appendix V III) An a tte m p t was made to e v a lu a te the assum ption by some t h a t a s i g n a l o f v a ry in g n a tu re p e rm its the s u b j e c t to a tte n d to the t e s t stim u lu s d e s p ite an i n t e r f e r e n c e e s t a b l i s h e d by t i n n i t u s . 57 (47, p . 52) The q u e s tio n s were d esign ed in an e f f o r t to d eterm in e the p resen c e o f t i n n i t u s , i t s s u b j e c t iv e i n f l u ence upon the e x e c u tio n o f a h e a rin g t e s t , and the su b j e c t ' s p re fe re n c e as to the type o f t e s t stim u lu s to which he a tte n d e d most e a s i l y . The q u e s tio n n a ir e c o n s is te d o f a s e r i e s o f th re e q u e s tio n s p re s e n te d to each s u b je c t a t the te r m in a tio n o f h i s h e a rin g t e s t s . The q u e s tio n n a ir e was conceived as a means o f a s s e s s in g the s u b je c tiv e in flu e n c e o f t i n n i t u s upon a u d io m etric re sp o n se s and to compare t h i s a p p r a i s a l w ith the f in d in g s of the au diom etric r e c o r d s . The f i r s t n in e s u b je c ts were g iven the q u e s t io n n a i r e to complete im m ediately a f t e r the e x p e rim e n ta l a u d io m e tric d a ta were o b ta in e d . Each o f the n ine s u b je c ts who com pleted the q u e s tio n n a ir e e x p erien c ed t i n n i t u s and re q u e s te d c l a r i f i c a t i o n of a t l e a s t one of the q u e s tio n s . Seven s u b je c ts d id n o t f u l l y u n d e rsta n d a t l e a s t two o f the q u e s tio n s . Four s u b j e c t s re q u e s te d a d d i t i o n a l in fo rm a tio n u s u a l ly r e l a t i v e to t h e i r head n o is e s b u t n o t d i r e c t l y r e l e v a n t to the q u e s t io n n a ir e . The l a t t e r s u b je c ts demons t r a t e d an in te n s e concern about t h e i r t i n n i t u s and the q u e s tio n n a ir e p r e s e n te d an o p p o rtu n ity f o r them to d is c u s s t h i s annoying a s p e c t o f t h e i r a u d ito ry problem . The e n t i r e q u e s tio n n a ir e procedu re was e n v isio n e d to consume no more th an fiv e m in u te s. However, in some c a s e s , a d is p r o p o r t i o n a t e amount of time was in v e s te d in th e com pletion of 58 the q u e s t io n n a ir e . In view o f t h i s developm ent, the com pletion o f the q u e s tio n n a ir e form by the s u b j e c t was abandoned. In an e f f o r t to in s u r e com prehension o f the q u e s tio n s and to reduce the le n g th o f tim e to o b ta in the answ ers, the e x p e rim e n te r o r a l l y p re s e n te d each q u e s tio n to the s u b j e c t and re c o rd e d the answers on the q u e s t i o n n a ir e form. A f te r the t e s t s had been a d m in iste re d and reco rd ed , d a ta from each o f the s u b - t e s t card s were t r a n s f e r r e d to the a p p ro p r ia te m aste r c a rd . The above procedure was follow ed fo r the e n t i r e e x p erim e n t. S t a t i s t i c a l P rocedures Two ty p es of n u m erica l d a ta were a v a i la b l e f o r s t a t i s t i c a l m a n ip u la tio n : a u d io m e tric re c o rd s and s u b j e c t q u e s t i o n n a i r e s . A udiom etric d a t a . The c o l l e c t e d d a ta were a rra y e d on le d g e r s h e e ts in a workable form t h a t f a c i l i t a t e d s t a t i s t i c a l tr e a tm e n t. The mean ascen ding and the mean d e s cending th r e s h o ld v a lu e s f o r each group and f o r each stim u lu s c o n d itio n were computed. Next, an i n d i c a t i o n of th e d i s p e r s i o n of the sc o re s was o b ta in e d by c a l c u l a t i n g th e v a ria n c e of th e s e v a lu e s . Using the g r e a t e s t d i f f e r ences between v a r i a n c e s , £ r a t i o s were computed to t e s t the hom ogeneity of the d i s p e r s i o n among th e d a t a . Since the f^ v a lu e s were n o t found s i g n i f i c a n t the n e x t s te p 59 t in vo lv ed th e c a l c u l a t i o n of the c r i t i c a l r a t i o n (£ ). The n u l l h y p o th e s is was to be r e j e c t e d i f th e c r i t i c a l r a t i o exceeded the 0.05 l e v e l o f c o n fid e n c e . F i n a l l y , the sums o f the a b s o lu te d i f f e r e n c e s betw een ascen d in g and d e sce n d ing th r e s h o ld s fo r each frequ ency e s t a b l i s h e d by pure i ; ton es and by w arble to n es were computed. This maneuver was e f f e c t e d in o rd e r to o b ta in an in d ex o f any d i s c r e p a n c ie s between ascendin g and descen d in g th r e s h o ld v a lu e s . S ub ject q u e s t i o n n a i r e s . A s e r i e s of th re e q u e s tio n s were p re s e n te d to each h a r d - o f - h e a r i n g s u b je c t in an e f f o r t to a p p ra is e the in flu e n c e of t i n n i t u s on re sp o n se s to the s t i m u l i . The com pleted q u e s t io n n a ir e s from each o f the h a r d - o f - h e a r in g s u b j e c t s were a v a i la b l e fo r com pari son. The p e rc e n ta g e of o c c u rren c e o f each p o s s ib le answer was computed fo r each q u e s tio n as a c h i square a n a ly s is would n o t y i e l d more m ean in g fu l d a ta . CHAPTER IV PRESENTATION AND ANALYSIS OF DATA Hie raw d a ta were o rg an iz ed to pro v id e com parisons o f the i n t e r r e l a t i o n s h i p s e x i s t i n g amongst th e v a rio u s s t i m u l i and the c o n d itio n s o f p r e s e n t a t i o n . For the sake of convenience and b r e v i t y each of the s t i m u l i and i t s manner of p r e s e n t a t i o n along w ith each sub-group of the e x p e rim e n ta l p o p u la tio n was g iv en the fo llo w in g a l p h a b e t i c a l and n u m erica l d e s ig n a tio n s : A. P r e s e n t a t io n o f pure tones by e arp h o n es. B. P r e s e n t a t io n o f w arble to n es by e arp h o n es. C. P r e s e n t a t io n o f w arble to n es by s o u n d fie ld . D. P r e s e n t a t io n o f re c o rd e d spondaic words by e a rp h o n e s . E. P r e s e n t a t io n of re c o rd e d spondaic words by so u n d fie Id. I . Normal h e a rin g I I . Moderate co ndu ctiv e lo ss I I I . Severe co n d u ctiv e lo ss IV. Moderate s e n s o r y -n e u r a l lo ss V. Severe s e n s o ry - n e u r a l lo ss The a r i t h m e t i c a l m a n ip u la tio n o f the d a ta u n d e r went the fo llo w in g s e q u e n t i a l tre a tm e n t: Means. Means were computed from the v a lu e s e s t a b lis h e d by each o f th e stim u lu s p r e s e n t a ti o n c o n d itio n s A, B, C, D, and E, o b ta in e d from each sub-grou p. Means were c a l c u l a t e d f o r each of the fo llo w in g c o n d itio n s : 1. Ascending measurements a t each frequency f o r each e a r . 2. Descending measurements a t each frequency fo r each e a r . 60 61 3. Combined ascen d in g and descen d in g measurements a t each frequency f o r each e a r . 4. S oun d fieId m easurements a t each freq u e n cy . 5. S o u n d fie ld m easurements o b ta in e d u sin g re c o rd e d sam ples o f speech. 6. Measurements a t the speech fre q u e n c ie s (500, 1,000 and 2,000 cps) o b ta in e d under c o n d itio n s A, B, and C. The r e s u l t s o f th e s e com putations are d is p la y e d in Tables 5 th ro ug h 11. V a ria n c e . The s t a t i s t i c a l v a lu e known as v a ria n c e r e p r e s e n t s an index o f the sp read of i n d i v i d u a l sc o re s around a common r e f e r e n c e p o i n t . "The com putation of the v a ria n c e i s the a r i t h m e t i c mean o f the squared d e v ia ti o n s o f the measurements from t h e i r m ean." (42, p. 85) V a ri ances were computed from the v a lu e s e s t a b l i s h e d by each of the s tim u lu s p r e s e n t a t i o n c o n d itio n s A, B, C, D, and E. V ariances were c a l c u l a t e d fo r each o f th e fo llo w in g con d i t i o n s : 1. Ascending m easurements a t each frequency f o r each e a r . 2. Descending measurements a t each frequency fo r each e a r . 3. Combined ascend ing and descen d in g m easure ments a t each frequency f o r each e a r . 4. S o u n d fie ld measurements a t each freq u e n cy . 5. S o u n d field measurements o b ta in e d u sin g re c o rd e d sam ples o f speech. 6. Measurements a t the speech fre q u e n c ie s (500, 1,000, and 2,000 cps) o b ta in e d under c o n d itio n s A, B, and C. The v a lu e s produced by th e s e com putations a re found in T ables 12 th ro u g h 15. The f_ r a t i o t e s t . A fte r computing the v a ria n c e s fo r the d i f f e r e n t c o n d itio n s in v o lv ed in the experim en t TABLE 5 M E A N ASCENDING (A) A ND DESCENDING (D) PURE TO N E EARPHONE THRESHOLDS3 FOR RIGHT EARS Frequency in cps Subject Group A 250 D A 500 D 1000 A D 2000 A D 4000 A D I -2 .5 -5 .0 -3 .2 -3 .8 -4 .2 -3 .8 -4 .0 -3 .8 2.2 1.8 I I 46.7 47.0 49.3 48.3 48.0 46.7 41.3 40.3 49.7 48 .0 I I I 67.0 64.7 75.3 72.7 73.3 73.0 71.0 71.0 85.7 84.3 IV 43.0 42.7 45.3 45.3 46.3 45.7 50.7 49.7 58.3 54.3 V 67.3 66.7 75.0 74.7 77.7 78.3 86.3 84.7 95.7 92.3 a In dB r e : 0.0002 dynes/cm^ ON ro TABLE 6 M E A N ASCENDING (A) A N D DESCENDING (D) PURE TO N E EARPHONE THRESHOLDS3 FOR LEFT EARS Frequency in cps Subject Group A 250 D A 500 D 1000 A D 2000 A D 4000 A D I -4 .5 -4 .8 -4 .8 -4 .2 -6 .8 -7 .0 -6 .0 - 6 .0 -1 .5 -1 .2 I I 45.0 45.0 46.7 46.3 43.7 43.3 39.3 39.0 49.0 48.0 I I I 69.3 67.7 75.7 73.3 79.3 78.3 76.3 76.7 92.3 90.3 IV 43.3 43.3 44.0 45.3 47.0 46.7 51.0 51.3 59.0 59.0 V 70.0 70.3 78.7 78.7 86.3 86.7 89.0 89.3 93.0 96.0 aIn dB r e : 0 .0 0 0 2 dynes/cm ^ O ' CO TABLE 7 M E A N ASCENDING (A) A ND DESCENDING (D) W A R BLE TO N E EARPHONE THRESHOLDS3 FOR RIGHT EARS Su bject Group Frequency in cps A 250 D A 500 D 1000 A D 2000 A D 4000 A D I -3 .2 -3 .2 -4 .5 -3 .5 -4 .8 -4 .2 -5 .5 -4 .8 2.8 2.2 I I 46.3 46.0 48.0 48.3 46.7 46.3 40.0 40.0 48.0 48.0 I I I 66.0 66.3 74.3 74.3 73.0 73.7 70.3 69.7 84.3 83.7 IV 42.3 42.3 45.0 44.7 46.3 46.0 49.7 49.3 55.3 55.3 V 67.3 ' 67.0 74.3 75.0 77.3 77.0 84.7 83.7 94.7 93.7 3In dB r e : 0 .0 0 0 2 dynes/cm ^ ON -P ' TABLE 8 M E A N ASCENDING (A) A ND DESCENDING (D) W A R BLE TO N E EARPHONE THRESHOLDS3 FOR LEFT EARS Frequency in cps Subject Group A 250 D A 500 D 1000 A D 2000 A D 4000 A D I -4 .5 -4 .8 -4 .8 -4 .2 -6 .8 -7 .0 -6 .0 -6 .0 -1 .5 -1 .2 I I 45.0 45.0 46.7 46.3 43.7 43.3 39.3 39.0 49.0 48.0 I I I 68.7 68.3 75.0 74.0 78.7 78.7 76.0 76.3 91.7 91.3 IV 43.3 43.3 44.0 44.0 47.0 46.7 51.7 52.0 59.3 59.7 V 70.0 70.3 79.3 79.3 86.7 85.7 88.3 88.3 94.3 94.3 aIn dB r e : 0 .0 0 0 2 dynes/cm ^ a\ Ln TABLE 9 M E A N ASCENDING (A) A ND DESCENDING (D) W A R BLE TO N E SOUNDFIELD THRESHOLDS3 Frequency in cps S ubject Group A 250 D A 500 D 1000 A D 2000 A D 4000 A D I -4 .0 -4 .0 -6 .2 -6 .0 -7 .5 -7 .0 -7 .2 -7 .8 - 2 .5 -1 .8 I I 44.3 43.0 46.0 45.7 44.7 44.3 39.0 38.0 45.7 45.7 I I I 64.7 64.7 70.7 71.0 72.0 71.7 69.0 69.7 84.0 83.7 IV 39.7 38.7 41.7 41.0 43.7 44.3 48.3 48.3 54.0 54.0 V 65.7 65.7 73.7 73.3 78.0 77.3 84.7 84.3 94.0 92.7 aIn dB r e : 0 ,0 0 0 2 dynes/cm ^ O ' O ' 67 TABLE 10 MEAN ASCENDING (A) AND DESCENDING (D) SPONDEE THRESHOLDS3 S u b ject Group R ight L e ft Sound f i e Id A D A D A D I 1.0 - 1 .2 - 0 .2 - 1 .0 -1 .0 -0 .2 I I 46.3 44.3 45 .0 41.7 45.7 4 3 .0 I I I 74.0 72.3 77.0 76.3 72.3 72.7 IV 53.0 51.0 50.7 49.3 50.3 49.7 V 86.7 84.7 90.3 89.3 87.7 86.0 'in dB r e : 0.0002 dynes/cm'1 d if f e r e n c e s among v a ria n c e s between groups were determ in ed . The c a l c u l a t i o n of i r a t i o s was c o n sid e re d a p p lic a b le here in o rd e r to t e s t the hom ogeneity o f v a r i a n c e . The £ v a lu e i s e s s e n t i a l l y the r a t i o o f the l a r g e r v a ria n c e to the s m a lle r v a ria n c e and i s employed to determ in e the s i g n i f i cance o f the d i f f e r e n c e betw een two v a r i a n c e s . (42, p . 224) The formula used in th e d e te rm in a tio n o f the t r a t i o was: f = - N, - C m.)' ¥ - - (» .)* TABLE 11 COMPARISON OF M EAN THRESHOLDS OBTAINED BY PURE TONES, WARBLE TONES, AND SPONDEE WORDS Subject Group Pure tone Average3 Warble tone Average3 Spondee words R ight L eft R ight L e ft Both R ight L eft Both I -3 .8 -5 .0 - 4 .5 -5 .8 -6 .1 -0 .1 -0 .6 -0 .6 I I 45.6 43.1 44.9 43.1 42.9 45.3 43.3 44.3 I I I 72.7 76.6 72.5 76.5 70.6 73.2 76.7 72.5 IV 47.2 47.6 46.8 47.5 44.5 52.0 50.0 50.0 V 79.4 84.8 78.7 84.6 78.6 85.7 89.8 86.8 a 500-2000 cps ON 00 TABLE 12 M EA N S (M) A ND VARIANCES (V) O F PURE TO N E (PT) A ND W A RBLE TO N E (WT) EARPHONE THRESHOLDS FOR RIGHT EARS Frequency in cps Group Stim ulus M 250 V M 500 V 1000 M V M 2000 V 4000 M V I PT WT -3 .8 -3 .2 25.6 32.3 -3 .5 -4 .0 30.2 31.5 -4 .0 -4 .5 21.5 18.5 - 3 .9 - 5 .1 35.4 23.4 2.0 2.5 29.8 35.0 I I PT WT 46.8 46.2 84.0 79.8 48.8 48.2 67.8 49.3 47.3 46.5 59.4 58.6 40.8 40.8 69.6 73.3 48.8 48.0 259.4 242.7 I I I PT WT 65.8 66.2 82.9 81.8 74.0 74.3 74.0 71.2 73.2 73.3 84.3 100.4 71.0 70.0 70.7 78.3 85.0 84.0 138.3 130.7 IV PT WT 42.8 42.3 82.4 75.7 45.3 44.8 61.2 65.5 46.0 46.2 47.3 48 .1 50.2 49.5 29.2 35.6 56.3 55.3 78.6 65.2 V PT W T 67.0 67.2 69.3 66.7 74.8 74.7 82.5 73.2 78.0 77.2 81.0 79.4 85.5 84.2 57.2 47.9 94.0 94.2 79.0 60.6 o' VO TABLE 13 M EA N S (M) A ND VARIANCES (V) OF PURE TO NE (PT) AND W A RBLE TO N E (WT) EARPHONE THRESHOLDS FOR LEFT EARS Subject Group Stim ulus Frequency in cps M 250 V M 500 V 1000 M V M 2000 V 4000 M V T PT - 4 .1 20.1 - 4 .0 16.5 -6 .5 14.0 - 4 .5 28.6 0.4 32.9 i W T -4 .6 20.7 -4 .5 14.8 -6 .9 13.0 -6 .0 21.0 -1 .4 34.9 T T PT 45.0 30.0 45.8 63.2 44.3 94.2 39.2 127.6 48.8 277.8 11 W T 45.0 93.3 46.5 45.2 43.5 88.6 39.2 145.9 48.5 311.9 T T T PT 68.5 51.0 74.5 130.6 78.8 108.1 76.5 90.2 91.3 61.0 111 W T 68.5 72.0 74.5 135.6 78.7 83.0 76.2 74.4 91.5 45.2 TT7 PT 43.3 70.1 44.7 30.2 46.8 55.6 51.2 29.4 59.0 82.3 IV W T 43.3 71.8 44.0 27.3 46.8 60.6 51.8 36.0 59.5 84.0 \J PT 70.2 34.5 78.7 108.0 86,5 37.0 89.2 60.9 94.5 80.6 W T 70.2 39.5 79.3 94.8 86.2 22.1 88.3 69.8 94.3 99.2 ^ TABLE 14 M EANS (M) AND VARIANCES (V) O F W A R BLE TO N E SOUNDFIELD THRESHOLDS Frequency in cps buDjecc Group M 250 V M 500 V M 1000 V M 2000 V i M ^000 V I - 4 .0 20.9 - 6 .1 14.7 -7 .2 13.2 -5 .0 50.0 - 2 .1 40.6 I I 43.7 77.0 45.8 49.9 44.5 80.6 38.5 122.0 45.7 234.8 I I I 64.7 70.6 70.8 61.6 71.8 64.0 69.3 60.8 83.8 110.1 IV 39.2 34.2 41.3 34.3 44 .0 47.3 48.3 28.8 54.0 47.3 V 65.7 31.8 73.5 62.0 77.7 57.7 84.5 45.6 93.3 83.4 72 TABLE 15 MEANS (M) AND VARIANCES (V) OF SPONDEE THRESHOLDS S ubject R ight L eft SoundfieId Group M V M V M V I - 0 .1 15.6 - 0 .6 15.2 -0 .6 9.0 I I 45.3 59.6 43.3 100.1 44.3 97.5 I I I 73.2 67.6 76.7 78.8 72.5 76.2 IV 52.0 37.7 50.0 36.7 50.0 30.0 V 85.7 90.5 89.8 65.2 86.8 105.0 From a c a s u a l o b s e rv a tio n of the ta b u la te d v a r i ances i t was a p p aren t t h a t the r a t i o o f the la r g e r v a r i ance to the sm a lle r v a ria n c e would n o t exceed a v alu e of one by a s u f f i c i e n t amount to produce s i g n i f i c a n t £ v a lu e s. In o rd e r to v e r i f y t h i s o b s e rv a tio n , £ r a t i o s were computed only fo r the l a r g e s t d if f e r e n c e s between v a r ia n c e s . I t was assumed t h a t i f the com putation of the .f v a lu e s fo r the g r e a t e s t d i f f e r e n c e s between v a ria n c e s were n o t s i g n i f i c a n t then sc o res fo r the sm a lle r d i f f e r e n c e s would n o t produce s i g n i f i c a n t v a lu e s . The r a t i o of the v a ria n c e of measurements o b tain ed by pure tones w ith earphones to the v a ria n c e o f m easure ments o b tain ed by w arble tones w ith earphones were 73 compared. These v a ria n c e s were compared a t each frequency fo r each e a r . In no case d id the r a t i o s ap pear s t a t i s t i c a l l y s i g n i f i c a n t . Ihe f r a t i o o f the l a r g e s t d i f f e r e n c e s betw een v a ria n c e s was computed to confirm t h i s o b s e r v a tio n . The l a r g e s t d i f f e r e n c e betw een two v a ria n c e s was found a t 1,000 cps f o r measurements o f the l e f t e a r . The v a ria n c e fo r pure to n es w ith earphones was 37.0 and the v a ria n c e fo r w arble to n es p re s e n te d by earphones was 2 2 .1 . The f^ r a t i o v a lu e which was a r e s u l t of t h i s com putation was 1.6 7 . This v a lu e f a l l s below t h a t which would imply the d i f f e r e n c e s between th e s e v a ria n c e s to be s t a t i s t i c a l l y s i g n i f i c a n t . An f r a t i o as la rg e as 2.48 or l a r g e r would be n e c e s s a ry to r e j e c t the n u l l h y p o th e s is . Ihe g r e a t e s t _f v a lu e computed fo r the norm al h e a r in g p o p u la tio n was 1.51 fo r the r i g h t e a r a t 2,000 c p s. An £ v a lu e o f 2.12 was r e q u ir e d f o r s t a t i s t i c a l s i g n i f i c a n c e . In view o f th e s e r e s u l t s , th e r e ap p ears to be no s i g n i f i c a n t d i f f e r ence between th r e s h o ld s o b ta in e d by e i t h e r pure to n es or w arble to n es p re s e n te d by earp h o n es. r a t i o t e s t . The form ula used in th e d e te r m in a tio n o f t h i s v a lu e was: S ig n if ic a n c e of d i f f e r e n c e s determ ined by the _t 74 S c ru tin y o f th e mean v a lu e s d em o nstrated l i t t l e o b se rv ab le d i f f e r e n c e s in average th r e s h o ld re sp o n se s to e i t h e r pure to n es or w arble to n e s . These d if f e r e n c e s appeared n e g l i g i b l e a t a l l f r e q u e n c ie s , fo r a l l s u b je c t gro u p s, fo r e i t h e r e a r , and fo r a l l stim u lu s p r e s e n t a t i o n c o n d itio n s . Using the same re a s o n in g employed e a r l i e r to reduce the number o f f^ v a lu e c a l c u l a t i o n s , _t r a t i o s were computed only fo r tho se means between which the g r e a t e s t d i f f e r e n c e s e x i s t e d . The assum ption employed h e re ag ain was t h a t c a l c u l a t i n g th e £ r a t i o s only f o r those means d is p la y in g the g r e a t e s t d if f e r e n c e would p ro v id e v a lu e s c l o s e s t to t h a t n e c e s s a ry f o r s i g n i f i c a n c e . C onsequently, i f th e s e r a t i o s were n o t s i g n i f i c a n t th en sm a lle r d i f f e r ences betw een means would n o t be s i g n i f i c a n t e i t h e r . In t h i s stu d y a _t r a t i o o f 1.96 or la r g e r was e s t a b l i s h e d as a c r i t e r i o n o f s i g n i f i c a n c e a t the f iv e p e r cen t l e v e l of c o n fid e n c e . In o th e r words, i f the d i f f e r ence between means was so g r e a t as to produce _t v a lu e s t h a t exceeded 1.9 6, the n u l l h y p o th e s is was r e j e c t e d . Com p u t a t i o n o f t^ r a t i o s only fo r th o se means between which the g r e a t e s t d i f f e r e n c e s e x i s t e d produced the v a lu e s shown in Table 16. These c a l c u l a t i o n s produced fiv e £ v a lu e s ; one f o r each stim u lu s p r e s e n t a t i o n c o n d itio n (A, B, C, D, and E ) . The l a r g e s t Jt v a lu e o b ta in e d was 1.80 fo r Group I under c o n d itio n D. In o r d e r o f t h e i r m agni tu d e s , th e rem aining t. v a lu e s o f 1 .56, 1.24, 0 .7 5 , and 0.55 75 were o b ta in e d fo r c o n d itio n s A, C, E, and B r e s p e c t i v e l y . In a l l i n s ta n c e s the _t r a t i o s f e l l s h o r t o f a s t a t i s t i c a l l y s i g n i f i c a n t l e v e l . These r e s u l t s in d ic a te d t h a t d i f f e r ences between mean ascen din g and mean d escending thresholdS | were n o t s i g n i f i c a n t . TABLE 16 FISHER t VALUES OBTAINED FOR GREATEST DIFFERENCES BETWEEN M EAN ASCENDING AND M EAN DESCENDING THRESHOLDS Stim ulus C ond ition S u b je ct Group Frequency Ear Mean D iffe re n c e t VaTue A I 250 R 2.5 1.56 B I 500 R 1.0 0.55 C V 4000 Bin 1.3 1.24 D I Speech R 2.2 1.80 E I I Speech Bin 2.7 0.75 F is h e r t v a lu e s were o b ta in e d f o r the l a r g e s t d if f e r e n c e s between mean measurements f o r pure tone speech fre q u e n c ie s and the mean measurements f o r re c o rd e d spondee words o b ta in e d by e a rp h o n es. Groups I I and I I I demon s t r a t e d t^ v a lu e s of 0.15 and 0.19 r e s p e c t i v e l y . These sc o re s were n o t s t a t i s t i c a l l y s i g n i f i c a n t . Groups I , IV, and V showed s i g n i f i c a n t t v a lu e s of 4 .6 6 , 2 .7 7 , and 2.45 r e s p e c t i v e l y . Very sm all mean d i f f e r e n c e s of 0.3 dB and 76 0 .5 dB were found fo r Groups I I and I I I . The mean d i f f e r ences f o r Groups I , IV, and V were 4 .4 dB, 4 .8 dB, and 6.3 dB r e s p e c t i v e l y . These d a ta are d is p la y e d in Table 17. TABLE 17 GREATEST t VALUES FOR MEAN DIFFERENCES BETWEEN TEST CONDITIONS "A" AND "D" Sub j e c t Group Ear Mean D iffe re n c e t Value P r o b a b i l i t y Leve 1 I L 4 .4 4.6 6 0.01 I I R 0.3 0.15 Not S i g n i f i c a n t I I I R 0 .5 0.19 Not S i g n i f i c a n t IV R 4 .8 2.77 0.01 V R 6.3 2.45 0.05 F is h e r _t v a lu e s were o b ta in e d f o r th e l a r g e s t d i f f e r e n c e s betw een mean m easurements f o r w arb le tone speech f r e q u e n c ie s and the mean measurements f o r re c o rd e d spondee words o b ta in e d by e a rp h o n es. Groups I I and I I I y ie ld e d v a lu e s o f 0.2 1 and 0.26 r e s p e c t i v e l y . These scores were n o t s t a t i s t i c a l l y s i g n i f i c a n t . Groups I , IV, and V showed v a lu e s o f 5 .6 5 , 2 .9 2 , and 2.77 which were s i g n i f i c an t to th e 0.01 l e v e l c o n fid e n c e . The mean d i f f e r e n c e s f o r Groups I I and I I I were v e ry sm all and amounted to 77 0 .4 dB and 0.7 dB r e s p e c t i v e l y . The mean d i f f e r e n c e f o r Groups I and IV was 5.2 dB and 7 .0 dB f o r Group V. These d a ta a re shown in Table 18. TABLE 18 GREATEST t. VALUES FOR MEAN DIFFERENCES BETWEEN TEST CONDITIONS "B" AND "D" S u b je ct Group Ear Mean D iffe re n c e t: Value P r o b a b i l i t y Leve 1 I L CM • 5.65 0 .0 1 I I R 0.4 0.21 Not S i g n i f i c a n t I I I R 0.7 0.26 Not S i g n i f i c a n t IV R 5.2 2.92 0.01 V R 7 .0 2.77 0.01 The Jt t e s t was a p p lie d to the l a r g e s t d i f f e r e n c e s between mean measurements f o r w arble tone speech fre q u e n c ie s and the mean measurements f o r re c o rd e d samples of speech o b ta in e d in a s o u n d f ie ld . The _t v a lu e s fo r Groups I I and I I I were 0 .54 and 0.86 r e s p e c t i v e l y . These v a lu e s were n o t s t a t i s t i c a l l y s i g n i f i c a n t . On the o th e r hand, the t: v a lu e s o b ta in e d f o r Groups I , IV, and V were found to be s i g n i f i c a n t a t th e 0 .0 1 p er c e n t l e v e l o f c o n fid e n c e . The _t v a lu e s fo r th e s e Groups were 3 .4 2 , 3 .3 9 , and 5.78 78 r e s p e c t i v e l y . A look a t the mean d i f f e r e n c e s f o r Groups I I and I I I show v a lu e s o f 1.4 dB and 1 9 dB r e s p e c t i v e l y . The mean d i f f e r e n c e s p ro ducin g the s i g n i f i c a n t £ sc o re s d em o n strate v a lu e s o f 5.5 dB f o r Groups I and IV and 8 .2 dB fo r Group V. These d a ta a re e x p re sse d in Table 19. TABLE 19 GREATEST t VALUES FOR M EAN DIFFERENCES BETWEEN TEST CONDITIONS "CM AND "E" S u b je ct Group Mean D iffe re n c e £ Value P r o b a b i l i t y L evel I 5.5 5.78 0.01 I I 1.4 0 .5 4 Not S i g n i f i c a n t I I I 1 .9 ' 0.87 Not S i g n i f i c a n t IV 5.5 3.42 0.01 V 8.2 3.39 0.01 The t v a lu e s o b ta in e d f o r the d i f f e r e n c e s between t o n a l s t i m u l i and speech r e c e p t i o n th r e s h o ld s d id n o t re a c h a s i g n i f i c a n t l e v e l fo r Groups I I and I I I . On the o th e r hand, Groups I , IV, and V d id show s i g n i f i c a n t _t v a lu e s f o r th e s e d i f f e r e n c e s . S c ru tin y o f the mean d i f f e r ences prod ucing th e s e sc o re s i n d ic a t e a c o n s i s t e n t r e l a t io n s h ip among the mean d i f f e r e n c e s w ith in each of the 79 fiv e e x p e rim e n ta l g ro u p s. There w ere, however, g r e a t changes in the mean d i f f e r e n c e s among the gro u p s. Sum o f the a b s o lu te d i f f e r e n c e s . An a sc e n d in g - | d escending th r e s h o ld e x p lo r a ti o n te c h n iq u e was d esig n ed in j t an e f f o r t to c o n tr o l the method by which the th r e s h o ld was 1 e s t a b l i s h e d . I t was p lanned t h a t i f th e s e two v a lu e s d i f f e r e d , t h e i r mean would be c o n sid e re d t h r e s h o ld . I t became i n c r e a s in g l y m a n if e s t as the d a ta were c o ll e c t e d t h a t th e ascen ding and d escending th r e s h o ld v a lu e s were more o f te n e q u a l th an d i f f e r e n t . From t h i s im p re ssio n grew th r e e a d d i t i o n a l q u e s tio n s n o t e n v isag e d in the o r i g i n a l e x p e rim e n ta l d e s ig n . These q u e s tio n s w ere: 1. Did d i f f e r e n c e s e x i s t between a u d ito r y t h r e s h o ld s e s t a b l i s h e d by ascend ing and descen d in g s t i m u l i p r e s e n t a t i o n methods? 2. Did l e s s d isc re p a n c y e x i s t between ascen din g and descending a u d ito r y th r e s h o ld s o b ta in e d w ith the w arble tone stim u lu s? 3. Were a l l fr e q u e n c ie s e q u a lly a f f e c t e d by any a sc e n d in g -d esc e n d in g method d isc re p a n c y ? The sums o f the a b s o lu te d i f f e r e n c e s between the ascending and descen ding t h r e s h o ld s f o r each frequency t e s t e d were c a l c u l a t e d fo r each e a r . This maneuver e n t a i l e d the sim ple a r i t h m e t i c com putation o f s u b t r a c t i n g the ascending t h r e s h o ld measurement from the descending th r e s h o ld measurement ( d is r e g a r d in g th e d i r e c t i o n o f the 80 d i f f e r e n c e ) and adding a l l th e s e v a lu e s t o g e t h e r . F i g u re s 4 through 8 show the sums of the a b s o lu te d if f e r e n c e s betw een ascending and descending measurements fo r each e x p e rim e n ta l group of s u b j e c t s . These curves in earphone p r e s e n t a t i o n i n d ic a t e t h a t w arble to n es produce f a r sm aller d i f f e r e n c e s betw een ascending and descending th re s h o ld measurements th an do pure to n e s . S c ru tin y o f the curves i n d i c a t e s t h a t the sum o f i n d iv i d u a l d i f f e r e n c e s i s always g r e a t e s t a t 4,000 cps. However, th e re was no a p p a re n t tr e n d i n d i c a t i n g t h a t a r e l a t i o n s h i p e x i s t e d between the frequency and the amount of d isc re p a n c y a t t h a t frequ ency. I t would seem re a so n a b le to assume from th e s e f in d in g s t h a t in d e a lin g w ith a p a r t i c u l a r s u b je c t the m agnitudes of the ascending and d escending th r e s h o ld d i s c re p a n c ie s found between w arble tone and pure tone e x p lo ra t i o n a re s i g n i f i c a n t . On the o th e r hand, in c o n s id e rin g a group o f s u b j e c t s , one must remember t h a t th e s e d i s c r e p a n c ie s e x i s t in b o th d i r e c t i o n s (p lu s and minus v a lu e s ) which tend to c a n c e l o u t each o t h e r 's e f f e c t . For t h i s re a s o n , no s i g n i f i c a n t _t v a lu e was found between d i f f e r ences of the mean ascend ing and the mean descendin g v a lu e s fo r any of the e x p e rim e n ta l grou ps. Q u e s tio n n a ir e . The d a ta d e riv e d from the q u e s t io n n a i r e were t r e a t e d sim ply by computing the p e rc en ta g e of tim es each p o s s ib le answer o c cu rred w ith in each group 81 80 T Pure to n e s R ---- 70-- Warble to n es 60 -- 50 -- 40 -- 30 -- 20 - - 10 -- 250 500 1000 2000 4000 Frequency F ig . 4 . --Sum o f the i n d iv i d u a l a b s o lu te d i f f e r e n c e s betw een ascend ing and d escen din g th r e s h o ld s fo r Group I o f s u b j e c t s . Some i n t e r e s t i n g r e l a t i o n s h i p s develop when the r e s u l t s o f t h i s com putation were compared. N inety per c e n t of the e n t i r e h a r d - o f - h e a r i n g popu l a t i o n used in t h i s stu d y e x p e rie n c e d t i n n i t u s . This p e r centage a g re es q u ite c lo s e l y w ith th e in c id e n c e of t i n n i t u s 82 m i— t (D X I •H U Q J a 80 R ----- Pure ton es 70 Warble tone 60 50 40 30 20 V 10 / 250 500 1000 2000 4000 Frequency F ig . 5 . --Sum of the i n d i v i d u a l a b s o lu te d i f f e r e n c e s between ascen d in g and descen din g th r e s h o ld s f o r Group I I ( e i g h t y - s i x p e r c e n t) in a survey o f 200 case h i s t o r i e s randomly s e l e c te d from the f i l e s of the O to lo g ic M edical Group. The in c id e n c e o f head n o is e ranged from a low o f e ig h ty p er c en t fo r Group IV to a h ig h of 100 p e r c en t fo r 83 CO 1— i <L> rO •r-l O CD Q 80 R ---- Pure ton es 70 Warble tones L - 60 50 40 30 20 10 250 500 1000 2000 4000 Frequency F ig . 6 . --Sum of the i n d i v i d u a l a b s o lu te d i f f e r e n c e s between ascen din g and descending t h r e s h o ld s fo r Group I I I Group V. These d a ta are p r e s e n te d in Table 20. In r e p ly to q u e s tio n number two, 72.2 p e r c en t of the h a r d - o f - h e a r in g s u b j e c t s f e l t t h a t t h e i r t i n n i t u s i n flu en c ed the accu racy of t h e i r h e a r in g t e s t . Of the su b j e c t s claim in g t i n n i t u s a l l th o se in Group V b e lie v e d t h e i r 84 CO r— H 0 ) rO •r-l O 0 ) Q 80 R ----- Pure ton es 70 Warble to n es 60 50 40 30 20 10 250 500 1000 2000 4000 Frequency F ig . 7 . --Sum o f the i n d i v i d u a l a b s o lu te d i f f e r e n c e s between ascending and descen ding th r e s h o ld s f o r Group IV head n o is e s i n t e r f e r e d w ith t h e i r perform ance d u rin g the a u d io m e tric e v a l u a t i o n . Group I I I claim ed to have the n e x t h ig h e s t t e s t i n t e r f e r e n c e w ith 92.8 p e r c e n t r e p o r t ing d i f f i c u l t y . Groups I I and IV r e p o r te d the low est i n c i dence of i n t e r f e r e n c e due to t i n n i t u s w ith p e rc e n ta g e s of 85 M 1 —I CD X I C D CD Q 80 R ----- Pure to nes Warble ton es 70 L - • 60 50 40 30 20 10 250 500 1000 2000 4000 Frequency F ig . 8 . --Sum o f the i n d i v i d u a l a b s o lu te d i f f e r e n c e s betw een ascend ing and d escend ing th r e s h o ld s f o r Group V 38.4 and 50.0 r e s p e c t i v e l y . These d a ta appear in Table 21. In comparing the a u d i b i l i t y o f the t e s t s t i m u l i a g a i n s t a background of t i n n i t u s , 100 p e r c e n t o f Group V claim ed t h a t the w arble s tim u lu s was most e a s i l y d i s c e r n i b l e . Group I I I a ls o r e p o r te d a p r e fe re n c e f o r w arble 86 TABLE 20 SUBJECT RESPONSES T O QUESTIONNAIRE NUM BER O N E Q u e stio n : Do you have head n o is e s ? Response S u b je ct Group T o ta l I I I I I IV V Yes Number 13 14 12 15 54 P e rce n tag e 86.6 93.3 8 0 .0 100 90.0 No Number 2 1 3 0 6 P e rce n tag e 13.3 6.6 20.0 0 .0 10.0 tone s i g n a l s . Of t h i s group, 57.1 p e r c e n t p r e f e r r e d w arble to n es w h ile 42.8 p e r c en t made re c o rd e d spondee words t h e i r f i r s t c h o ic e . On the o th e r hand, Groups I I and IV dem o n strated a p r e fe r e n c e f o r the re c o rd e d speech samples as b e in g most a u d ib le th ro u g h t h e i r t i n n i t u s . The speech s t i m u l i were p r e f e r r e d by 61.5 p e r c en t o f th e su b j e c t s in Group I I and 66.6 p e r c e n t o f tho se in Group IV. Groups I I and I I I showed alm ost e q u a l and c o n t r a s t i n g c h o ic e s o f s t i m u l i betw een w arble to n e s and re c o rd e d sp eech. In t h i s r e g a r d , Group I I p r e f e r r e d spondee word s t i m u l i 61.5 p e r c en t of the time w h ile 57.1 p e r c e n t o f TABLE 21 SUBJECT RESPONSES T O QUESTIONNAIRE NUM BER T W O Q u e stio n : Do you b e lie v e your head n o is e s i n t e r f e r e w ith th e a ccu racy of your h e a rin g t e s t ? S u b je c t Group T o ta l N-54 Response I I Ns 13 I I I N = 14 IV N = 12 V N= 15 Yes Number 5 13 6 15 39 P e rcen tag e 38.4 92.8 50.0 100 72.2 No Number 8 1 6 0 15 P e rcen tag e 61.5 7 .1 50.0 0.0 27.7 Group I I I p r e f e r r e d w arble to n e s . On the o th e r hand, 3 8 .4 p e r c e n t of Group I I p r e f e r r e d w arble to n e s and 4 2 .1 p e r cen t o f Group I I I chose spondee w ords. These d a ta are p r e s e n te d in Table 22. I t would app ear t h e r e f o r e from th e s e f in d in g s t h a t tho se s u b j e c t s w ith more se v ere a u d io m e tr ic lo s s e s show g r e a t e r p r e f e r e n c e f o r an a b s t r a c t s tim u lu s . I t i s i n t e r e s t i n g to no te t h a t in no case was th e pure tone s i g n a l e v e r th e p r e f e r r e d s tim u lu s . I t seems abu n d an tly e v id e n t from t h i s f in d in g t h a t th e w arble tone TABLE 22 "FIRST PREFERENCE" RESPONSES T O QUESTIONNAIRE N U M BER TH REE Responses Su bject Group T o ta l N = 54 I I N= 13 I I I N= 14 IV N= 12 V N = 15 Number 0 0 0 0 0 Steady Tones P ercentage - - - - - Number 8 6 8 0 22 Words P ercentage 61.5 42.8 66.6 40.7 Number 5 8 4 15 32 Warble Tones Percentage 38.4 57.1 33.3 100 59.2 oo 00 89 s tim u lu s i s c o n sid e re d by th e s e s u b j e c t s to be more e a s i l y p e rc e iv e d through th e i n t e r f e r e n c e o f t i n n i t u s th an the pure tone s i g n a l . I n t e r p r e t a t i o n o f d a t a . On the b a s i s o f th e r e s u l t s o f t h i s e x p erim e n t, d a ta may be i n t e r p r e t e d as f o l l o w s : 1. D e sp ite the s p e c t r a l com plexity o f the w arble tone s tim u lu s , h e a r in g th r e s h o ld s e s t a b l i s h e d by t h i s means were e s s e n t i a l l y the same m agnitude as tho se e s t a b l i s h e d by pure to n e s . I t would seem re a s o n a b le to say t h a t so long as the freq uency m odulated s i g n a l p o s s e s s e s the same g e n e r a l p i t c h as the pure tone s i g n a l , the t h r e s h o ld s w i l l be c l i n i c a l l y i d e n t i c a l . G re a te r d i s t o r t i o n o f th e pure tone s tim u lu s through the a l t e r a t i o n of the c e n t r a l f r e quency or the r a t e and range of m o du latio n w i l l su b s e q u e n tly in f lu e n c e a s u b j e c t 's re sp o n se s to i t as a t e s t s i g n a l . In o th e r w ords, the more m odulatio n we in tr o d u c e , the g r e a t e r the d isc re p a n c y between pure tone and w arble tone t h r e s h o ld s . 2. The fin d in g t h a t a c c u ra te a u d ito r y t h r e s h o ld measurements may be o b ta in e d by an ascending or descen d in g e x p lo r a to r y tec h n iq u e lend s su p p o rt to a p re v io u s i n v e s t i g a tio n (57) t h a t ad v o ca te s the use of e i t h e r method. 3. Warble tone as a stim u lu s o f f e r e d more s t a b l e th r e s h o ld s in t h a t d i f f e r e n c e s betw een i n d i v i d u a l a sce n d ing and descending t h r e s h o ld s were much s m a lle r th a n the 90 co rre sp o n d in g v a lu e s o b ta in e d by pure to n e s . A lthough th e r e was a p p a r e n tly no r e l a t i o n s h i p betw een the freq u en cy and the m agnitude o f the d i f f e r e n c e a t t h a t freq u en cy , g r e a t e s t d i f f e r e n c e s o c c u rre d a t 4,000 c p s. These d i f f e r ences may be e x p la in e d i n two ways: T in n itu s w i t h in th e h ig h frequency range could s e t up a p a t t e r n o f in te rf e re n c e to produce g r e a t e r d is c re p a n c y a t 4,0 0 0 c p s. U nlike the pure to n e , the v a ry in g n a tu r e of the w arble tone p e rm its the t e s t tone to sta n d o u t of a background o f t i n n i t u s f o r e a s i e r r e c o g n i ti o n . Secondly, the s h o r t wave le n g th of a 4,000 cps tone m ight e s t a b l i s h a p a t t e r n of s ta n d in g waves w ith in the e x t e r n a l a u d ito r y c a n a l. These s ta n d in g waves co u ld , by t h e i r n a tu r e , confound the ta s k of th r e s h o ld d e te r m in a tio n . However, w arble tone s t i m u l i do n o t i n t e r a c t l ik e pure to n es to produce s ta n d in g waves. 4. T hreshold d i f f e r e n c e s v a r ie d betw een the to n a l s i g n a ls (warble to n e s and pure to n e s ) and re c o rd e d spondee words in r e l a t i o n to th e type and degree of h e a r in g im p a ir ment. I n d iv id u a ls w ith co n d u ctiv e lo s s e s d em on strated the l e a s t t h r e s h o ld d i f f e r e n c e between t o n a l and spondee s t i m u l i . The g r e a t e s t d i f f e r e n c e s were produced by sev ere s e n s o r y - n e u r a l im pairm ents. Normal h e a r in g s u b j e c t s and tho se w ith m oderate s e n s o r y - n e u r a l lo s s e s dem onstrated very s i m il a r th r e s h o ld d i f f e r e n c e s . A lthough th e s e d i f f e r e n c e s were s t a t i s t i c a l l y s i g n i f i c a n t , they were s t i l l sm all and 91 could be c o n sid e re d c l i n i c a l l y n o n - s i g n i f i c a n t . These f in d in g s seemed to o f f e r f u r t h e r i n v e s t i g a t i v e evid en ce to th e t r a d i t i o n a l method o f e s t im a t i n g re sp o n se s to speech from a th r e e frequency average o f pure tone th r e s h o ld v a lu e s . (14) 5. The g r e a t m a jo r ity ( n in e ty p e r c e n t) o f the h a r d - o f - h e a r i n g p o p u la tio n e x p e rie n c e d t i n n i t u s . Moreover, a la rg e segment o f the h e a rin g handicapped b e lie v e d t h a t t i n n i t u s in flu e n c e d the accu racy o f th r e s h o ld determ ination. 6. A ll h a r d - o f - h e a r i n g s u b j e c t s observed g r e a t e r ease of l i s t e n i n g t o the w arble tone s t i m u l i th an to the pure tone s i g n a l s . In t h i s re g a rd the s u b j e c t w ith a se v ere s e n s o r y - n e u r a l im pairm ent p r e f e r r e d th e w arble stim u lu s even above samples o f speech . The observed p r e fe re n c e m ight be based on the in c r e a s e d d is c r im in a to r y d i f f i c u l t y en co u n tere d by th o se w ith sev ere s e n s o r y -n e u r a l l o s s e s . Thompson and Hoel (89) found t h a t s u b je c ts w ith f l a t s e n s o r y - n e u r a l h e a rin g lo s s e s w ith l e v e ls o f 40 to 49 dB and g r e a t e r dem on strated a marked r e d u c tio n in i n t e l l i g i b i l i t y . F urtherm ore, the g r e a t e r th e lo s s the p o o re r the d i s c r i m i n a t i o n s c o re . Egan (48) i d e n t i f i e d th r e e i n t e n s i t y l e v e ls in the d e te r m in a tio n o f th e speech th r e s h o ld . The th r e s h o ld of d e t e c t a b i l i t y i s e s t a b l i s h e d as t h a t p o in t along an i n t e n s i t y s c a le where the s u b j e c t i s j u s t a b le to d e t e c t the p re se n c e o f speech w ith o u t b ein g a b le to i d e n t i f y the 92 sounds. The th r e s h o ld o f p e r c e p t i b i l i t y i s re g a rd e d as th e i n t e n s i t y l e v e l where the o b s e rv e r i s a b le to i d e n t i f y or u n d e rs ta n d w ith c o n s id e r a b le d i f f i c u l t y the sam ples o f speech p r e s e n te d to him. In e s t a b l i s h i n g th e t h r e s h o ld o f i n t e l l i g i b i l i t y the s u b je c t i s i n s t r u c t e d to i d e n t i f y the l e v e l a t which he can u n d e rs ta n d the t e s t item s w i t h out e f f o r t . The speech r e c e p t i o n th r e s h o ld p ro ced ure u t i l i z e d in t h i s experim ent was b e lie v e d to be e s s e n t i a l l y i d e n t i c a l to the t o n a l th r e s h o ld te c h n iq u e i n s o f a r as the stim u lu s was a re c o rd e d spondee word to which the o b s e rv e r responded c o r r e c t l y or i n c o r r e c t l y . In e s t a b l i s h i n g the t o n a l th r e s h o ld , th e s tim u lu s was a tone o r tone complex to which the s u b j e c t d id o r d id n o t resp o n d . We m ight p o s t u l a t e t h a t the s u b j e c t confused th r e s h o ld of d e t e c t a b i l i t y w ith the th r e s h o ld o f p e r c e p t i b i l i t y in h i s a tte m p t to i d e n t i f y samples o f speech . Con s e q u e n tly , in h i s e f f o r t to compare s t i m u l i he b e lie v e d he more e a s i l y p e rc e iv e d t o n a l s t i m u l i th an he d id sam ples o f speech. CHAPTER V SUMMARY, CONCLUSIONS AND IMPLICATIONS Summary Problem. The b a s ic o b j e c ti v e o f th e study was to i n v e s t i g a t e the a u d io m e tric re s p o n se s o f norm al and h a rd - o f - h e a r in g a d u lt s t o pure to n e s , w arble to n e s , and recorded spondee words. Answers to the fo llo w in g s p e c i f i c q u e s t io n s were sought i n t h i s stu d y : 1. Do d i f f e r e n c e s e x i s t in t h r e s h o ld v a lu e s f o r pure to nes and w arble to n es p r e s e n te d by earphones? 2. Do d i f f e r e n c e s e x i s t in t h r e s h o ld v a lu e s f o r w arble to n es and re c o rd e d spondee words p r e s e n te d by earphones? 3. Do d i f f e r e n c e s e x i s t in th r e s h o ld v a lu e s f o r w arble ton es and re c o rd e d spondee words p re s e n te d in a so u n d fie Id? 4. Does th e type o f h e a r in g lo s s c o n tr i b u te to any v a r i a t i o n s in t h r e s h o ld v a lu e s among the s tim u li? 5. Does th e degree o f h e a rin g lo s s c o n tr i b u te to any v a r i a t i o n s in t h r e s h o ld v a lu e s among the s tim u li? 6. Do the t h r e s h o ld v a lu e s o b ta in e d u sin g the s e l e c te d s t i m u l i d i f f e r s i g n i f i c a n t l y fo r any o f th e fre q u e n c ie s te s te d ? 7. Do d i f f e r e n c e s e x i s t betw een a u d ito r y 93 94 th r e s h o ld s e s t a b l i s h e d by a sce n d in g and d escending s t i m u l i p r e s e n t a t i o n methods? 8. Does le s s d is c re p a n c y e x i s t between ascen din g and d escen d in g a u d ito r y th r e s h o ld s o b ta in e d w ith the w arble tone s tim u lu s th an w ith the pure tone stim u lu s? 9. Are a l l fre q u e n c ie s e q u a lly a f f e c t e d by any a sc e n d in g -d e sc e n d in g method d i f f e r e n t i a l ? S u b je c ts . A udiom etric t e s t s were conducted on a t o t a l o f e ig h ty norm al and h a r d - o f - h e a r i n g a d u l t s . The s u b j e c t s were d iv id e d i n t o f iv e groups acc o rd in g to p a th o logy o f lo s s and degree o f im pairm ent measured in d e c i b e l s . The norm al h e a rin g group was composed of female employees o f the O to lo g ic M edical Group. The p a th o lo g ic groups composed o f f i f t e e n members each were r e c r u i t e d from th o se p a t i e n t s v i s i t i n g the "Group" fo r m ed ica l c o n s u l ta ti o n . Those p a t i e n t s s a t i s f y i n g th e e x p e rim e n ta l c r i t e r i a were s e l e c t e d as s u b j e c t s i f s u f f i c i e n t time p e rm itte d the c o l l e c t i o n o f d a ta in one s i t t i n g . S tr i n g e n t c r i t e r i a were e s t a b l i s h e d fo r the s e l e c t i o n o f s u b j e c t s in o rd e r to c o n tr o l the in flu e n c e o f e x tra n e o u s c o n d itio n s on th r e s h o ld v a lu e s . E quipm ent. The d a ta were c o l l e c t e d in two c o n tig u ous a c o u s t i c a l l y i s o l a t e d rooms w ith known n o is e a t t e n u a t i o n v a lu e s . A B eltone two chan n el pure tone and speech audiom eter in s e r i e s w ith headphones, a t u r n t a b l e , lo u d sp e a k e r, and A l l is o n Warble Tone A dapter formed the 95 p r i n c i p a l equipment used in the ex p erim en t. E xperim ental p r o c e d u r e s . The d a ta c o l l e c t i o n procedure c o n s is te d o f f i v e a u d io m e tric t e s t s a d m in iste re d to a l l e ig h ty s u b j e c t s . These t e s t s were: A. P r e s e n t a t io n o f pure to n es by e a rp h o n es. B. P r e s e n t a t io n o f w arble to n es by e arp h o n es. C. P r e s e n t a t io n o f w arble to n es by s o u n d f ie ld . D. P r e s e n t a t io n o f rec o rd ed spondaic words by e a rp h o n e s . E. P r e s e n t a t io n o f re c o rd e d spondaic words by sou n d fie Id. In an e f f o r t to in s u re the r e l i a b i l i t y of r e s u l t s a p r e a rran g ed b u t random p r e s e n t a t i o n o f t e s t s t i m u l i and e x p e rim e n ta l c o n d itio n s was employed. The t e s t exp erim ent was p e r i o d i c a l l y c a l i b r a t e d and was c o n tin u o u sly un der the * s c r u t in y of th e e x p e rim e n te r. Each s u b je c t was given un ifo rm i n s t r u c t i o n s fo r resp o n d in g to the s t i m u l i . These t e s t s i g n a l s were d e liv e r e d to the s u b je c t in a c o n tr o l le d environm ent. A sta n d a rd th r e s h o ld d e te r m in a tio n method was d esig n ed and r i g i d l y adhered to th ro u g h o u t the ex p erim e n t. The f i n a l phase o f the experim en t was the i n t e r r o g a tio n o f each h a r d - o f - h e a r in g s u b je c t in an e f f o r t to a p p ra is e the in f lu e n c e o f t i n n i t u s on re s p o n se s to the e x p e rim e n ta l a u d ito r y s t i m u l i . A n a ly sis of the d a t a . Means and v a r ia n c e s were 96 computed from the v a lu e s e s t a b l i s h e d by each o f the s tim u lu s p r e s e n t a t i o n c o n d itio n s A, B, C, D, and E o b ta in e d from each su b -g ro u p . In o rd e r to t e s t th e hom ogeneity o f v a ria n c e o f the d i s t r i b u t i o n s , £ r a t i o s were computed. These r a t i o s were computed only f o r th e l a r g e s t d if f e r e n c e s betw een v a r i a n c e s . When a l l f^ r a t i o s were found to be n o n - s i g n i f i c a n t , _t r a t i o t e s t s were a p p lie d to determ ine the s i g n i f i c a n c e o f the d i f f e r e n c e s betw een means. Finally, the sums o f the a b s o lu te d i f f e r e n c e s between the ascen din g and descen d in g th r e s h o ld s fo r each frequ en cy were c a l c u l a t e d . This l a s t com putation was perform ed to o b ta in an index o f the d is c re p a n c y betw een asce n d in g and descending t h r e s h o l d s . A q u e s tio n n a ir e c o n s i s t i n g o f th r e e q u e s tio n s was su b m itted to each o f th e h a r d - o f - h e a r i n g s u b j e c t s . The q u e s tio n s were d e sig n e d to a p p ra is e th e in flu e n c e o f head n o ise on th e re s p o n se s to the t e s t s t i m u l i . The p e r c e n t age o f o ccu rren c e o f each p o s s ib l e answer was computed fo r each q u e s tio n . Summary o f th e r e s u l t s . The p r i n c i p a l fin d in g s o f t h i s stu d y may be summarized as fo llo w s: 1. The _t v a lu e s c a l c u l a t e d f o r the g r e a t e s t d i f f e r e n c e s betw een mean m easurements fo r pure tone and w arble tone s t i m u l i p re s e n te d thro u g h earph ones were n o t s i g n i f i c a n t . In o rd e r o f t h e i r m ag n itu d es, _t v a lu e s o f 1.80, 1 .5 6, 1.24, 0 .7 5 , and 0 .5 5 were o b ta in e d fo r C o n d itio n s D, A, C, E, and B r e s p e c t i v e l y . 2. The _t v a lu e s c a l c u l a t e d fo r th e g r e a t e s t d i f f e r e n c e s betw een mean measurements f o r pure tone s t i m u l i and mean measurements f o r re c o rd e d spondee words p re s e n te d thro u g h earphones were n o t s i g n i f i c a n t f o r Groups I I and I I I who y ie ld e d sc o re s o f 0.15 and 0.19 r e s p e c t i v e l y . However, Groups I , IV, and V showed s i g n i f i c a n t £ v a lu e s o f 4 .6 6 , 2 .77, and 2.45 r e s p e c t i v e l y . The mean d i f f e r e n c e s t h a t produced th e se l a t t e r £ v a lu e s were 4 .4 dB, and 6.3 dB and were co n sid ere d c l i n i c a l l y n o n - s i g n i f i c a n t . 3. The _t v a lu e s computed only f o r the g r e a t e s t d if f e r e n c e s between mean measurements fo r w arble tone s t i m u l i and mean measurements f o r rec o rd ed spondee words p re s e n te d throug h earphones produced sc o re s o f 0 .2 1 and 0.26 fo r Groups I I and I I I . These v a lu e s were n o t s t a t i s t i c a l l y s i g n i f i c a n t . Groups I , IV, and V y ie ld e d t: sc o re s o f 5.65, 2.92, and 2.77 which r e p r e s e n te d s i g n i f i c a n c e a t th e 0.01 le v e l o f c o n fid e n c e . The mean d if f e r e n c e fo r Groups I and IV was 5.2 dB and 7 .0 dB fo r Group V. D esp ite t h e i r s t a t i s t i c a l s i g n i f i c a n c e , th e se mean d if f e r e n c e s were c o n sid e re d c l i n i c a l l y n o n - s i g n i f i c a n t . 4. The _t t e s t a p p lie d to the g r e a t e s t d if f e r e n c e s between mean measurements f o r w arble tone s t i m u l i and the mean measurements f o r re c o rd e d samples of speech p re s e n te d in a s o u n d fie ld produced n o n - s i g n i f i c a n t v a lu e s o f 0.54 and 0.86 fo r Groups I I and I I I r e s p e c t i v e l y . Groups I , IV, and V y ie ld e d s i g n i f i c a n t £ v a lu e s o f 3 .4 2 , 3 .39 and 5.78 r e s p e c t i v e l y . The mean d i f f e r e n c e s t h a t produced th e s e l a t t e r t: v a lu e s were 5.5 dB f o r Groups I and IV and 8 .2 dB f o r Group V. These d i f f e r e n c e s were a g ain c o n sid e re d c l i n i c a l l y n o n - s i g n i f i c a n t . 5. The f^ r a t i o computed f o r the g r e a t e s t difference between v a ria n c e s o f m easurements o b ta in e d by pure to n es and w arble to n es throug h earphones was 1 .6 7 . An £ v a lu e o f 2.12 was r e q u ir e d f o r s t a t i s t i c a l s i g n i f i c a n c e . The d i f f e r e n c e s betw een mean th r e s h o ld s o b ta in e d by pure to n es and w arble to n es through earphones were n e g l i g i b l e a t a l l f r e q u e n c ie s , fo r a l l s u b j e c t groups and f o r e i t h e r e a r . 6. The £ v a lu e s computed f o r the g r e a t e s t d i f f e r ences between mean ascen d in g and mean d e scen d in g th r e s h o ld s fo r each stim u lu s p r e s e n t a t i o n c o n d itio n were 1.56, 0 .5 5 , 1 .2 4, 1.8 0, and 0.75 f o r C o n d itio n s A, B, C, D, and E r e s p e c t i v e l y . These v a lu e s were n o t c o n sid e re d to be s i g n i f i c a n t sin c e a _t sc o re o f 2.0 0 r e p r e s e n te d s i g n i f i cance a t the f iv e p e r c e n t l e v e l . 7. Less d isc re p a n c y e x i s t s betw een i n d i v i d u a l ascen ding and descen d in g t h r e s h o ld s o b ta in e d by w arble tone s t i m u l i th an c o rre sp o n d in g t h r e s h o ld s o b ta in e d by pure tone s i g n a l s . Far s m a lle r v a lu e s were o b ta in e d f o r w arble to n es th a n fo r pure to n e s by summing the a b s o lu te t h r e s h o ld d i f f e r e n c e s and d i s r e g a r d i n g the d i r e c t i o n o f each d i f f e r e n c e . 99 8. A ll fre q u e n c ie s d em onstrated d is c r e p a n c ie s between in d iv i d u a l ascen din g and descen din g t h r e s h o ld s . There was, however, no i n d i c a t i o n t h a t the frequency and the amount o f d isc re p a n c y a t t h a t freq uency were r e l a t e d . However, the sums o f th e a b s o lu te d i f f e r e n c e s between pure tone and w arble tone th re s h o ld s were g r e a t e s t a t 4,0 00 cps f o r each e x p e rim e n ta l group. 9. Data o b ta in e d from Q uestion Number One showed the m a jo rity o f each h a r d - o f - h e a r in g sub-group to e x p e r i ence t i n n i t u s . In o rd e r o f in c r e a s in g m agnitude, the pe rc en ta g e o f in c id e n c e of head n o ise was 8 0 .0 , 8 6 .6 , 93.3, and 100 p er c e n t fo r Groups IV, I I , I I I , and V respectively. 10. In resp o n se to Q uestio n Number Two 72.2 p er c en t of the h a rd - o f - h e a r in g p o p u la tio n r e p o r te d t h a t t i n n i t u s in flu e n c e d the accuracy o f t h e i r h e a rin g t e s t . Groups I I I and V r e p o r te d the h ig h e s t in c id e n c e of t e s t in te r f e r e n c e w ith sc o re s of 92.8 and 100 p e r c en t r e s p e c t i v e l y . Groups I I and IV r e p o r te d the low est in cid en c e of t e s t i n te r f e r e n c e w ith p e rc e n ta g e re sp o n se s of 38.4 and 50.0 r e s p e c t i v e l y . In o th e r words, th o se e x p e rim e n ta l groups d e m o n stra tin g the g r e a t e s t degree o f lo ss a ls o claim the g r e a t e s t degree o f t e s t i n t e r f e r e n c e due to t i n n i t u s . 11. Those s u b je c ts w ith the g r e a t e r degree of h e a rin g lo s s showed p re fe re n c e f o r w arble s t i m u l i r a t h e r than fo r rec o rd ed samples o f speech a cco rd in g to resp o n se s to Q uestion Number Three. In no case was the pure tone 100 s i g n a l the p r e f e r r e d s tim u lu s . In a s s e s s in g the a u d i b i l i t y o f the t e s t s t i m u l i a g a i n s t a background o f t i n n i t u s , Groups I I I (se v ere c o n d u ctiv e ) and V (se v ere senso ry -n eu ral) claim ed t h a t the w arble s t i m u l i were more e a s i l y a tte n d e d to th an the pure tone and re c o rd e d spondee s i g n a l s . Groups I I and IV r e p o r te d a p r e f e re n c e f o r th e re c o rd e d spondaic words. C onclusions The r e s u l t s o f t h i s stu d y as o b ta in e d from t h i s p a r t i c u l a r sample of s u b je c ts and w ith in th e framework of the e x p e rim e n ta l d e sig n lead to the fo llo w in g c o n c lu s io n s : 1„ A ud itory t h r e s h o ld s o b ta in e d by e i t h e r pure to n es o r frequency m odulated to n es a re g e n e r a l l y s i m i l a r . 2. The m agnitude o f th e mean d i f f e r e n c e s between w arble to n es and pure to n es i s n o t r e l a t e d to the frequency a t which the th r e s h o ld s a re o b ta in e d . 3. There i s g r e a t e r d is c re p a n c y betw een in d iv i d u a l ascending and descending th r e s h o ld s o b ta in e d by pure tgn es th an co rre sp o n d in g th r e s h o ld s o b ta in e d by w arble to n e s . A ll fre q u e n c ie s show d is c r e p a n c ie s betw een in d iv i d u a l ascending and descend ing t h r e s h o ld s . There i s no i n d i c a t i o n t h a t the frequency and th e amount of d isc re p a n c y a t t h a t frequency a re r e l a t e d . However, the sums o f the in d iv i d u a l d i f f e r e n c e s between pure tone and w arble tone th r e s h o ld s a re g r e a t e s t a t 4,000 cps. 101 4. T h resh old d i f f e r e n c e s v a ry between th e t o n a l s t i m u l i (warble to n es and pure to n e s ) and spondee words in r e l a t i o n to the type and degree of h e a rin g im pairm ent. I n d iv id u a ls w ith co n ductiv e lo s s e s dem o n strate the l e a s t t h r e s h o ld d i f f e r e n c e between t o n a l and spondee s t i m u l i . The g r e a t e s t d i f f e r e n c e s a re produced by severe s e n s o r y - n e u r a l im pairm en ts. Normal h e a rin g s u b je c ts and th o se w ith m oderate s e n s o r y - n e u r a l lo s s e s e x h i b i t very s i m i l a r th r e s h o ld d i f f e r e n c e s . These d i f f e r e n c e s are n o t c o n sid e re d c l i n i c a l l y s i g n i f i c a n t . 5. Those s u b j e c t s d e m o n stra tin g the g r e a t e s t degree o f h e a rin g im pairm ent a ls o c laim the g r e a t e s t i n c i dence o f t e s t i n t e r f e r e n c e from t h e i r t i n n i t u s . 6. S u b je c ts w ith sev ere h e a rin g im pairm ents p r e f e r w arble tone s t i m u l i to re c o rd e d samples o f speech . On the o th e r hand, s u b j e c t s w ith m oderate im pairm ents p r e f e r re c o rd e d spondee words as a t e s t s tim u lu s . S ug g estio n s f o r F u r th e r R esearch The t r a d i t i o n a l method employed in h e a rin g a id e v a lu a tio n in which a id ed and unaided t h r e s h o ld s and d i s c rim in a tio n sc o re s a re e s t a b l i s h e d w ith samples of speech has r e c e n t l y come un der sharp c r i t i c i s m . Some r e s e a r c h e r s have found l i t t l e r e l i a b i l i t y betw een t e s t - r e t e s t v a lu e s u sin g the same a i d s . The s o u n d fie ld use o f w arble tone n o t only would y i e l d the frequency by frequency resp o n se 102 c h a r a c t e r i s t i c o f an a id b u t m ight o f f e r more r e l i a b l e t h r e s h o ld s . A stu d y d esig n ed to c o r r e l a t e w arble tone th r e s h o ld resp o n se w ith and w ith o u t an aid to u s e r s a t i s f a c t i o n m ight rew ard the c l i n i c a l a u d io l o g i s t w ith a more a c c u ra te method of p r e s c r i b i n g a h e a rin g a id . C u rren t p r a c t i c e u t i l i z e s v a r io u s n o is e s of d i f f e r e n t spectrum s to e lim in a te th e p a r t i c i p a t i o n of the o p p o s ite (u n te s te d ) e a r d u rin g a u d io m etric e v a lu a tio n . D e sp ite the number o f masking media a v a ila b le fo r u se , a u d i o l o g i s t s s t i l l e n co u n ter d i f f i c u l t y in e s t a b l i s h i n g v a l i d th r e s h o ld s . I t does n o t seem u n rea so n a b le to p o s t u l a t e t h a t a m odulated tone w ith the same base frequency as the t e s t to n e , a p p lie d t o the o p p o site e a r would o f f e r e f f e c t i v e m asking. E x p erim e n tatio n u sin g v a rio u s r a t e s and ran g e s o f m odu latio n may o f f e r an a d d i t i o n a l and more e f f e c t i v e masking a g e n t. LITERATURE CITED 1. AMERICAN MEDICAL ASSOCIATION. R eport o f the c o u n c il on p h y s ic a l th e ra p y . Minimum re q u ire m e n ts fo r a c c e p ta b le a u d io m ete rs. J . Amer. Med. Assoc. 113:732. 1939. 2. _______ . T e n ta tiv e s ta n d a rd p ro cedu re f o r e v a lu a - t i n g the p e rc e n ta g e of u s e f u l h e a rin g lo s s in m edico le g a l c a s e s . J . Amer. Med. 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P s y c h o l. 5 1 :5 2 1 -5 2 2 . 1938. 1 2 3 4 5 6 7 8 9 10 11 12 APPENDIX I ONE AIR CONDUCTION AUDIOGRAMS OF TWENTY NORM AL HEARING SUBJECTS (GROUP I ) Ear F requency in cps 250 500 1000 2000 4000 R 0 0 0 0 5 L 0 0 -5 5 10 R 5 10 5 -5 0 L 0 0 -5 -10 -5 R -5 -5 -10 5 0 L -5 -5 -10 -10 0 R -5 -5 -5 -10 -5 L -5 -5 -10 -10 -10 R -10 -10 -10 -10 -5 L -10 -10 -10 -10 -10 R 5 0 -5 -10 0 L 5 -5 0 -5 0 R 5 5 0 -10 5 L 5 5 5 -5 10 R -10 -10 -5 -5 -5 L -10 -5 -10 -10 -5 R 0 -5 -10 0 5 L -5 0 -10 5 0 R 5 -5 0 0 0 L 0 -10 0 -5 -10 R 0 -5 -5 5 10 L -5 -5 -10 -10 0 R 0 -10 -10 5 10 L -5 -5 -10 10 10 112 APPENDIX I C ontinued 113 S u b je c t Number Ear Frequency in cps 250 500 1000 2000 4000 13 R -10 -10 -10 -10 5 L -10 -10 -10 -10 -5 14 R -10 -5 -5 -10 10 L -5 0 -5 -10 5 15 R -5 0 -5 -5 5 L 0 0 -5 -5 10 16 R -5 -5 -5 -5 0 L -5 0 -5 -5 0 17 R 5 5 5 -5 0 L -10 0 -10 -10 5 18 R -5 -10 -10 -10 0 L -5 -10 -10 -10 -5 19 R -5 0 -5 -10 -5 L -5 -5 -5 0 0 20 R -5 0 5 10 10 - L -5 -10 -5 0 5 114 APPENDIX I I PURE TONE AIR CONDUCTION AND BONE CONDUCTION AUDIOGRAMS OF GROUP I I S u b je c t Number BC o r AC T e st ]?ar F requen cy i n cps D a l 250 500 1000 2000 4000 BC R 10 10 15 15 10 L 15 10 10 15 10 28 a p R 60 60 50 55 40 n v L 50 55 50 50 45 R P R 15 10 15 20 30 D U L 15 10 20 20 40 29 A P R 55 55 60 60 75 n u L 45 50 60 60 85 R P R 15 10 15 5 35 D U L 5 15 5 5 15 37 A P R 45 45 50 45 85 n U L 40 50 45 40 65 R P R 15 5 10 5 20 D U L 10 5 5 15 15 46 A P R 50 50 50 45 50 n U L 45 50 45 50 45 R P R 20 20 10 5 10 D U L 15 10 10 5 10 47 A P R 55 65 60 45 45 A U L 60 55 55 50 35 APPENDIX I I C ontinued 115 S u b je c t Number BC o r AC T e s t 1 F req u en cy i n cps E<a IT 250 500 1 0 0 0 2 0 0 0 4000 R -5 -5 0 1 0 2 0 L -5 -5 -5 -5 15 51 A P R 40 55 40 45 65 L 45 35 2 0 2 0 60 BC R -5 -5 -5 5 1 0 L 1 0 0 0 5 1 0 52 AC R 35 35 40 30 35 L 50 40 35 35 45 BC R 1 0 1 0 5 10 2 0 L 1 0 15 1 0 1 0 2 0 56 AC R 50 45 40 45 65 L 45 50 50 45 65 BC R -5 0 5 -5 15 L -5 -5 5 0 15 58 AC R 30 40 40 35 60 L 30 40 40 30 60 BC R 0 0 0 5 15 L 5 5 1 0 1 0 2 0 65 AC R 40 45 45 45 55 L 45 50 50 50 65 BC R 1 0 0 5 -5 -5 L -5 0 0 -5 0 66 AC R 40 45 35 30 35 L 30 35 30 2 0 2 0 APPENDIX I I C ontinued 116 S u b je c t Number BC o r AC T e s t E ar F req u en cy i n cps 250 500 1000 2000 4000 BC R 10 15 5 0 10 L 10 10 10 5 10 70 AC R 45 55 50 35 40 L 45 50 45 40 35 BC R 15 15 5 5 10 73 L 10 15 10 0 10 a r R 60 55 55 35 40 n u L 60 60 55 35 45 BC R 15 10 10 5 10 L 10 10 5 5 10 75 A P R 50 40 45 35 30 L 45 40 45 30 30 BC R 10 10 15 10 10 L 10 5 10 10 5 78 AC R 45 45 50 40 35 L 50 45 50 40 35 117 APPENDIX I I I PURE TONE AIR CONDUCTION A ND BONE CONDUCTION AUDIOGRAMS O F GROUP I I I S u b je c t Number BC o r AC T e s t E ar F requ ency i n cps 250 500 1000 2000 4000 RP R 25 25 30 20 40 22 Du L 20 25 35 25 40 AC R 75 80 85 65 90 L 70 75 90 70 95 BC R 20 30 40 35 45 L 20 25 35 30 35 26 AC R 65 85 90 80 100 L 65 70 80 75 80 BC R 20 20 20 30 45 L 15 20 35 35 50 27 Af R 60 65 65 70 90 n U L 55 60 85 80 100 RP R 25 35 40 20 25 CL L 25 40 35 40 45 31 AC R 70 80 90 75 75 L 80 90 80 95 95 R P R 20 30 30 35 50 D U L 30 45 50 50 50 34 AP R 75 85 80 85 100 nU L 80 95 95 100 100 APPENDIX I I I C ontinued 118 S u b je c t Number BC o r AC T e s t E ar F req u en cy i n cps 250 500 1000 2000 4000 BC R 25 30 20 25 50 L 25 30 25 20 55 40 AC R 70 75 65 65 90 L 65 75 70 65 95 BC R 30 30 30 20 35 L 40 45 40 25 40 42 AC R 70 75 60 65 85 L 80 90 85 70 85 BC R 15 20 30 35 45 L 20 25 25 15 35 44 AC R 55 65 70 80 95 L 60 60 65 65 85 BC R 35 35 35 20 25 49 L 30 40 50 25 40 AC R 70 75 70 60 65 L 75 90 95 70 80 BC R 5 15 25 20 30 50 L 20 25 35 40 45 AC R 40 60 75 65 70 L 55 60 80 85 95 BC R 35 35 35 25 35 53 L 10 20 30 30 40 AC R 70 75 80 70 75 L 65 70 70 75 85 119 APPENDIX I I I C ontinued S u b je c t Number BC o r AC T e st E ar F requency i n cps 250 500 1000 2000 4000 BC R 30 20 15 25 35 L 35 25 15 35 40 55 AC R 70 65 60 60 80 L 80 75 65 75 90 BC R 30 45 35 45 40 L 35 40 50 35 45 57 AC R 70 90 75 85 75 L 80 85 90 75 95 RP R 25 20 15 20 45 DO L 20 25 25 20 45 69 a r R 70 75 65 65 90 £ \ \ J L 65 75 70 65 95 RP R 35 40 25 30 40 D \ j L 20 20 30 30 35 80 AC R 75 80 70 75 90 L 65 65 70 80 90 120 APPENDIX IV PURE TONE AIR CONDUCTION AND BONE CONDUCTION AUDIOGRAMS OF GROUP IV S u b je c t BC o r AC F requen cy i n cps E ar Number T e s t 250 500 1000 2000 4000 BC R 35 50 40 45 L 25 35 45 50 - - 25 AC R 30 45 45 45 70 L 25 35 40 45 50 BC R 50 50 50 __ L ------ 45 50 55 60 30 AC R 50 45 45 45 50 L 45 45 45 50 60 BC R 45 35 40 45 60 L 40 45 40 45 60 33 AC R 40 35 40 45 55 L 35 40 45 50 60 BC R 40 55 35 60 L 50 50 45 65 - - 35 AC R 35 45 40 55 70 L 40 45 40 60 65 BC R . . 65 50 45 40 L 40 40 50 65 36 AC R 60 55 45 50 35 L 55 40 40 50 60 APPENDIX IV C ontinued 121 S u b je c t Number BC o r AC T e s t E ar F req u en cy i n cps 250 500 1000 2000 4000 R P R 45 30 40 50 65 DU L 45 40 50 55 60 39 A P R 35 35 40 45 60 nij L 40 40 50 45 60 RP R 45 45 50 65 DU L 40 45 45 40 60 41 AP R 50 40 45 50 60 n u L 35 45 50 40 60 BC R 40 55 40 65 60 L - - 35 55 60 60 45 AT R 35 55 40 60 60 nU L 50 35 50 60 60 RP R 40 40 50 60 DU L 40 40 50 55 65 54 AP R 35 45 55 55 65 nU L 40 45 55 50 60 BC R 30 40 45 65 65 L ------ 55 40 50 - - 61 AP R 35 35 50 60 60 n v L 55 55 40 45 85 RP R 45 60 DU L 45 45 45 50 60 63 AC R 55 40 60 55 60 L 40 45 45 50 50 APPENDIX IV C ontinued 122 S u b je c t Number BC o r AC T e s t E ar F req u en cy i n cps 250 500 1000 2000 4000 RP R 40 55 55 50 DV-> L 50 55 60 65 68 AP R 40 50 55 50 60 L 55 50 55 60 60 RP R 40 40 55 60 D O L 45 50 35 50 60 72 AP R 55 40 40 50 60 n v L 40 50 35 55 55 RP R 55 50 50 55 D O L 55 50 45 60 77 AP R 40 55 55 50 50 n O L 50 50 60 55 50 BC R 40 40 60 79 L - - 55 55 50 60 AP R 55 60 40 40 55 n O L 45 50 50 45 55 123 APPENDIX V PURE TONE AIR CONDUCTION AND BONE CONDUCTION AUDIOGRAMS OF G RO UP V Subj e c t BC o r AC F requency in cps Number T e s t E ar 250 500 1000 2000 4000 21 BC AC R L R L 70 65 80 95 90 80 95 90 100 100 23 BC AC R L R L 55 60 60 60 65 60 75 75 75 75 80 75 24 BC AC R L R L 70 65 85 75 85 80 90 85 100 95 32 BC AC R L R L 75 80 65 65 70 75 90 95 95 38 BC AC R L R L 75 80 60 65 75 70 85 85 95 100 95 APPENDIX V C ontinued 124 S u b je c t Number BC o r AC T e s t F requen cy in cps ssrr 250 500 1000 2000 4000 R . . L — R 65 75 80 95 100 L 75 90 85 95 100 R L R 80 70 65 90 100 L 65 80 90 95 100 R L 65 60 R 50 65 65 85 95 L 60 75 85 90 95 R L R 70 85 90 100 100 L 70 85 85 95 100 R 65 L R 70 75 65 70 100 L 75 70 85 80 100 R L R 65 75 90 80 80 L 75 90 95 95 80 43 48 59 60 62 64 BC AC BC AC BC AC BC AC BC AC BC AC 125 APPENDIX V C ontinued S u b je c t Number BC o r AC T e s t E ar F requ ency in cps - 250 500 1000 2000 4000 R BC L 67 A P R 60 75 90 80 85 L 70 90 95 95 85 BC R L 71 A P R 65 70 75 80 95 L 70 70 80 90 100 BC R L 74 A P R 65 90 70 85 100 £\\j L 75 85 90 75 100 BC R L 65 76 A P R 75 90 80 90 95 n U L 70 65 90 80 95 126 APPENDIX VI DATA COLLECTION FORMS Case # A 250 500 1000 2000 4000 H Aa < * > W CO a o M Da o S z ! H O a a M a 2 < A D W PM H a 9 D M Case # w a A A scending t h r e s h o ld D D escen d in g t h r e s h o ld M Mean o f a s c e n d in g and d e sc e n d in g t h r e s h o ld s WARBLE TONES EARPHONES LEFT RIGHT 2 O > 2 O > o > w PJ o > w RECORDED SPONDEES SOUNDFIELD 2 D > > M 2 O M X o o 3 r t 3 e n > a o 127 128 APPENDIX VI C ontinued CASE # 250 500 1000 2000 4000 W A R B L E TONES SOUNDFIELD A D M WARBLE TONES PURE TONES SOUNDFIELD EARPHONES BINAURAL LEFT RIGHT LEFT RIGHT 2 o > 2 a > 2 o > 2 O > 2 a > NAM E CASE AGE SEX DIAG1 RECORDED SPONDEE W ORDS o * « = c n w C/i SOUNDFIELD LEFT RIGHT 2 o > 2 a > 2 o > 621 panujrjuoQ xA xiONaddV 130 APPENDIX V II CID AUDITORY TESTS W --I A AND B T e s t W--IA T e s t W--IB Greyhound B a s e b a ll P la y g ro u n d T o o th b ru sh Schoolboy S ta irw a y G randson Mushroom In k w e ll Cowboy D aybreak F a re w e ll W hitew ash Ic e b e rg Doormat H orseshoe Pancake N o rth w est Woodwork Pancake M ousetrap R a ilr o a d A rm chair Inkw e11 Eardrum P lay g ro u n d S ta irw a y M oustrap H e a d lig h t A irp la n e Cowboy A irp la n e B irth d a y Woodwork Oa tine a 1 Sidew alk Duckpond O atm eal R a ilr o a d Eardrum Sidew alk T o o th b ru sh B a s e b a ll Greyhound Hotdog F a r e w e ll P adlock B irth d a y P adlock G randson Hardware H othouse Mushroom D raw bridge W hitew ash I c e b e rg Hardware Doormat Hotdog S choolboy Workshop H othouse S u n set Duckpond H orseshoe D aybreak H e a d lig h t Workshop A rm chair S u n se t D raw bridge N o rth w est APPENDIX V III 131 SUBJECT QUESTIONNAIRE PLEASE ANSW ER THE FOLLOWING QUESTIONS BY PLACING A M A RK IN THE APPROPRIATE SPACE. 1. DO Y O U HAVE HEAD NOISES? YES N O_____ ANSW ER THE FOLLOWING QUESTIONS ONLY IF YOU HAVE HEAD NOISES. 2. DO Y O U BELIEVE YOUR HEAD NOISES INTERFERE WITH THE ACCURACY OF YOUR HEARING TEST? YES N O_____ 3. OF THE THREE TESTS (STEADY TONES, WORDS, A N D W ARBLE TONES) RANK YOUR PREFERENCE AS TO YOUR EASE OF LISTENING. USE THE NUM BERS 1, 2, 3 TO EXPRESS THIS PREFERENCE. STEADY TONES W ORDS W ARBLE TONES

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Creator Hughes, Richard Llewellyn (author)

Core Title An Experimental Study Of Auditory Thresholds Of Adults For Warble Tone, Pure Tone, And Recorded Speech

Contributor Digitized by ProQuest (provenance)

Degree Doctor of Philosophy

Degree Program Speech

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag OAI-PMH Harvest,Theater

Language English

Advisor Garwood, Victor P. (committee chair), [Howell], William (committee member), Perkins, William H. (committee member)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c18-286050

Unique identifier UC11358914

Identifier 6305055.pdf (filename),usctheses-c18-286050 (legacy record id)

Legacy Identifier 6305055.pdf

Dmrecord 286050

Document Type Dissertation

Rights Hughes, Richard Llewellyn

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA

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University of Southern California Dissertations and Theses