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The Effects Of Harmonic Distortion On Sentence Intelligibility Of Hypacusic Adults

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The Effects Of Harmonic Distortion On Sentence Intelligibility Of Hypacusic Adults

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Content THE E F F E C T S OF HARMONIC DISTORTION ON SEN TEN C E INTELLIGIBILITY OF HYPACUSIC ADULTS by Paul W e sle y Hartm an A D isse r ta tio n P r e se n te d to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In P a r tia l F u lfillm en t of the R eq u irem en ts for the D egree DOCTOR OF PHILOSOPHY (C om m unicative D iso rd ers) June 1971 71-27,923 HARTM AN, P a u l W esley, 1931- TH E EFFECTS OF H A R M O N IC DISTORTION O N SENTENCE INTELLIGIBILITY OF HYPACUSIC ADULTS. U n iv e r s ity o f Southern C a lif o r n i a , Ph.D., 1971 Speech P a th o lo g y | University Microfilms, A X E R O X C om pany, Ann Arbor, M ichigan THIS DISSERTATION HAS BEEN MICROFILMED EXACTLY AS RECEIVED UNIVERSITY O F SOU THERN CALIFORNIA T H E G R A D U A T E S C H O O L U N IV E R S IT Y PA R K L O S A N G E L E S . C A L IF O R N IA 9 0 0 0 7 This dts)ertatiop, writt ....... under the direction of h.MdJ. Dissertation Com mittee, and approved by all its members, has been presented to and accepted by The Gradu ate School, in partial fulfillment of require ments of the degree of D O C T O R OF P H IL O S O P H Y f 'T n Dean Date.F.ehximi:y...l3.21... AC KNOW L E D G E M E N TS S in c e r e thanks is due M r. D onald K reb s, D ir e c to r , San D ieg o S p eech and H earin g C en ter for h is a s s is t a n c e and u n d ersta n d in g , D r. R ob ert Sandlin, D ir e c to r o f P r o f e s s io n a l S e r v ic e s , San D ieg o S p eech and H ea rin g C en ter fo r h is g u id a n ce and d ir e ctio n , and D r. John S in c la ir , C h ief E n g in ee r , H ea rin g A id D iv is io n , Z en ith R adio C orp oration for h is g u id a n ce and Z enith R adio C o rp o ra tio n for u s e o f equip m ent. S in c e r e thanks is due a ls o to M r. R o b ert R ich m on d , E x ec u tiv e A s s is ta n t to the P r e s id e n t, V o ic e p r in t L a b o r a to r ie s for h is a s s is t a n c e in obtaining the sound sp e c tr o g r a p h s u s e d in th is study. TA BLE OF CONTENTS P age LIST O F TABLES .................................................................................................... iv LIST O F FIGURES .................................................................................................... v Chapter I THE PR O BLEM ................................................................................... 1 D efinitions of T er m s Statem ent of the P ro b lem E xp erim en tal H yp oth eses S ig n ifica n ce o f the P r o b lem II REVIEW OF THE LITE R A TU R E .............................................. 8 III M E T H O D ..................................................................................................... 29 Subjects M aterials Equipm ent and R ecordin g P ro c ed u r e P ro ced u re IV RESULTS .................................................................................................. 52 S ta tistica l P ro ced u re Su m m ary V DISCUSSION OF R ESULTS ........................................................... 62 VI SUMMARY AND C O N C L U S IO N S................................................. 70 Su m m ary C o n clu sion s A P P E N D IC E S Appendix A: A uditory T e st S en ten ces Taped from PAL#8 . . 76 A ppendix B: A n sw er Sh eets for In tellig ib ility T ests ............... 82 A ppendix C: G ray's Reading T e st ........................................................ 88 A ppendix D: A u d iom etric and M ed ical Data for Subjects . . . 90 A ppendix E: Raw S c o r es on Sen ten ce In tellig ib ility T e s t s ................................................................................... 93 B IB L IO G R A P H Y ........................................................................................................... 96 iii LIST O F T A B L E S T ab le P a g e 1 E x p e r im e n ta l D e sig n for O rd er o f P r e se n ta tio n o f S e n ten ce T e s ts and C o n d i t i o n s ........................................... 50 2 A n a ly sis o f V a r ia n c e A m ong M eans ................................. 54 3 S en ten ce In te llig ib ility S c o r e s fo r the F iv e T e s ts and C on d ition s C om b in ed .......................................... 56 4 M ean S en ten ce I n te llig ib ility S c o r e s fo r W ide and N arrow B andw idth by Second and Third H a rm o n ic D isto r tio n ....................................................................... 57 5 M ean P e r c e n t C o r r e c t fo r S en ten ce In te llig ib ility S c o r e s for the F iv e C ond itions on the F iv e T e s ts . . 58 6 S ta tistic a l C o m p a r iso n s b e tw een S c o r e s for "A dults" and " G e r ia tr ic s" on C on d ition s 2, 3, 4 , 5, SRT, M CL, and SDS ................................................................ 60 iv LIST O F FIGURES F ig u re P a g e 1 D iagram s d em on strating Linear and n o n -lin ea r am p lification ..................................................................................... 17 2 Sim plified sch em atic diagram of Zenith distortion gen erator ..................................................................................... 34 3 Block diagram of apparatus u sed to produce and record d istorted te st t a p e s ........................................................ 35 4 F requency resp o n se and 30 p ercen t second harm onic distortion cu rv es of the Zenith distortion gen erator ........................................................................................ 37 5 Frequency resp o n se and 30 p ercen t third harm onic distortion cu rv es of the Zenith distortion g en erator . 37 6 B ru el and K jaer graphic le v el recording of rela tiv e inten sity variation s of cock tail party n o ise as a function of tim e.................................................................................... 41 7 Speech sp ectrograp h s com paring un distorted and d istorted conditions for the sa m e sp eech sounds . . . 42 8 Speech spectrograp h s com paring un distorted and d istorted conditions for the sa m e sp eech sounds . . . 43 9 Speech spectrograp h s com paring undistorted and d istorted conditions for the sa m e sp eech sounds . . . 44 10 Speech sp ectrograp h s com paring undistorted and d istorted conditions for the sa m e sp eech sounds . . . 45 11 Mean s c o r e s for the five treatm en t conditions . . . . 55 v C H A P T E R I THE PR O B L E M The c h o ic e o f h ea rin g a id s u se d for the c lin ic a l evalu ation o f the h earin g im p a ired is in flu en ced by the k n ow led ge of the a c o u stic p a r a m e te r s of the in str u m e n ts, c h a r a c t e r is tic s of the h ea rin g l o s s of the individual, and the e x p e r ie n c e o f the exam in in g a u d io lo g ist. The a c o u stic p a r a m e te r s m o s t often c o n sid e re d for se le c tio n and evaluation o f h ea rin g a id s a r e a c o u stic gain, m a x im u m p ow er output, freq u en cy ran ge and the contou r o f the freq u en cy en v elo p e. Although the m e a s u r e m e n t o f gain, output, and bandwidth a r e im p o r tant m e a su r e m e n t c r it e r ia that should be c o n sid e re d , one other im p ortant p a r a m e te r is the d isto r tio n c h a r a c te r is tic of the in s tr u m ent. A ll a m p lifie r s p ro d u ce m e a s u r a b le d isto rtio n . Low fid elity a m p lifie r s u se d for h ea rin g aid a m p lifica tio n prod u ce r e la tiv e ly high d isto rtio n . It is co m m o n ly a s s u m e d by a u d io lo g ists that d isto rtio n in a h earin g aid is u n d e sir a b le b e c a u s e of d e le te r io u s e ffe c ts on the 1 2 q u a lity and in te llig ib ility o f s p e e c h s ig n a ls . T h e r e is no a p p a ren t a g r e e m e n t in the lit e r a tu r e a s to how m u ch d isto r tio n is p e r m is s ib le b e fo r e it b e c o m e s u n d e sir a b le , n or is th e r e a g r e e m e n t a s to w h a t typ e o f d isto r tio n is m o s t d isr u p tiv e o f c la r ity and q u a lity for sp e ec h . Sh epard c ite s at le a s t on e in sta n c e in w h ic h d isto r tio n can be c o n s id e r e d a d e s ir a b le c h a r a c t e r is t ic . * He h a s s u g g e ste d that it m a y b e p o s s ib le to su p p ly m is s in g ga p s in the freq u en cy e n v elo p e o f a low fid e lity a m p lifie r output b y th e d e lib e r a te in trod u ction o f h a r m o n ic d isto r tio n . The d isto r tio n in trod u ced w ould: (1) c o m p le m e n t the h a r m o n ic s tr u c tu r e o f s p e e c h and (2) enh an ce s p e e c h d is c r im in a tio n by fillin g in th e m is s in g fr e q u e n c ie s. The p o s s ib ilit y that h a r m o n ic d isto r tio n m a y b e a d e s ir a b le c h a r a c t e r is t ic o f h ea rin g aid function is c o n tr a r y to th e opinion of m o s t a u d io lo g is ts . D isto r tio n is an u n d e sir a b le p rod u ct if a p o s itiv e c o r r e la tio n e x is t s b etw een a m p lifie d sound and s p e e c h in te llig ib ility . W atson and T olan p o stu la ted that "odd h a r m o n ic d isto r tio n (3rd, 5th, 7th) is m u ch m o r e d is t r e s s in g to the e a r and to in te llig ib ility than F r e d e r ic k H. Shepard, Jr. , "A New A m p lifie r H aving C h a r a c t e r is t ic s S im ila r to T h o se o f the Human E a r and Its A p p lica tio n to the P r o b le m o f D e a fn e ss , " T he L a r y n g o sc o p e , L (A ugust, 1940), 767. i o ev en harm onic d isto rtio n (2nd, 4th, 6th." D avis and S ilv erm a n state, "The seco n d harm on ic is the g r ea test offender w ith r e s p e c t to 3 the in telligib ility of sp eech . " J e rg e r p rop oses interm odulation d is- 4 tortion as m o st sig n ifica n t. O lsen and C arhart, in their stud ies of distortion products in hearing a id s, conclude that harm on ic and in ter m odulation d isto rtio n have no relia b le or sy stem a tic effects on d is crim ination for sp eech through h earin g a id s. Sp eech d iscrim in a tio n s c o r e s in quiet and n o ise d e liv ered via a high fid elity s y ste m and through three d ifferen t low fid elity s y ste m s varyin g in d eg ree of h ar- 5 m on ic and inter m odulation d isto rtio n , w e re e sse n tia lly unchanged. T hey concluded th at the only p h y sica l m e a su rem en t having any con sisten t relation to sp eech d iscrim in a tio n w a s the freq u en cy bandwidth of the hearing a id . L ick lid er sta tes that even harm onic distortion is Leland A . W atson and T hom as Tolan, H earing T e s ts and H earing Instrum ents (B altim ore: The W illiam s and W ilkins Com pany, 1949), 333. 3 H allow ell D avis and R ichard S ilverm an , H earing and D eaf n e s s (2nd ed. r e v . ; New York: H olt, R inehart and W inston, Inc. , I960), 316. 4 Jam es J e r g e r , "B ehavioral C o rrela tes of H earing Aid P e r fo r m a n ce ," BuJletin_^f_Prosth^in_R^esearch, BR 10-7 (Spring, 1967), 73. 5 Wayne O lsen and R aym ond C arhart, "D evelopm ent of T est P ro ced u res for B inau ral H earing A id s, " B u lletin of P ro sth etic R e se a r c h , BR 1 0 -7 (Spring, 1967), 48. l e s s d etr im e n ta l than odd h a rm o n ic d isto rtio n to the in te llig ib ility of sp e ec h . ^ D efin ition s of T er m s T he follow ing d efin itio n s p r o c e e d fro m g e n e r a l to s p e c ific t e r m s and a re ex tra p o la ted from m o r e d e ta iled d efin ition s for p u r p o s e s o f c la r ity . N o n -lin e a r D is to r tio n : A g e n e r a l te r m ap p lied to any d is to r tion w h ich o c c u r s in an a m p lifie r w hen the output is not p rop ortion al to the am p litu d e o f the input. A m p litu d e D is to r tio n : A m o r e s p e c ific te r m for n o n -lin e a r d isto r tio n and r e fe r s to change in the output o f a w a v e form so that it is no lo n g e r p rop ortion al to the o r ig in a l am p litu d e of the input w a v e fo rm . H arm on ic D is to r tio n : The p rodu ction o f h a rm o n ic freq u en cies at the output by the n o n -lin e a r ity o f an a m p lifie r . H arm on ic d is to r tion is u su a lly a function of the am p litu d e of the input sig n a l. A lso: the im p a ir m en t o f fid elity c a u sed by th e g en era tio n o f new J. C. R. L ick lid er, " E ffects o f A m p litu d e D isto rtio n Upon the In te llig ib ility o f S p eech , " The Journal of the A c o u stic a l S o c ie ty of A m e r ic a . XVIII (O ctober, 1946), 432. freq u en cies in the output that a r e h a rm o n ics o f the freq u en cies c o n tained in the input signal. Second H arm onic D istortion (Even H arm on ic): A form of am plitude distortion generated as a r esu lt of a sy m m e tr ic a l peak c lip ping of a w ave form . In a sy m m e tr ic a l peak clipping, the w a v e form is clipped on only one sid e o f the tim e a x is. H arm onics generated a re even m u ltip les of the fundamental frequency (2nd, 4th, 6th). Third H arm onic D istortion (Odd H arm onic): A form of a m p li tude distortion gen erated as a r e su lt o f sy m m e tr ica l peak clipping of a w a v e form . In s y m m e tr ic a l peak clipping, the peaks of the w ave on both sid e s of the tim e a x is a r e clipped off, and the' h arm on ics g e n e r ated a r e odd m u ltip les of the fundam ental frequency (3rd, 5th, 7th). Interm odulation D isto r tio n : The production of new freq u en cies at the output by the in teraction of freq u en cies p resen t at the input. This distortion is in the form of sum s and d ifferen ces of the frequen c ie s at the input. D istorted S e n ten ce s: F or the p u rp oses o f this experim ent, d istorted sen ten ces m ay be defined as th ose te s t sen ten ces p r o c e s s e d through a v ariab le distortion a m p lifier to d e lib era tely induce second or third harm on ic distortion. 6 U nd istorted S en ten ces: T est s e n te n c e s not p a sse d through the d istortion a m p lifier m en tion ed above. Statem en t of the P ro b lem The pu rp ose o f th is study w as to in v e stig a te the effects of secon d h arm on ic and th ird harm onic d isto rtio n on sen ten ce in te llig i bility. E xp erim en tal H yp oth eses The follow ing h y p o th eses w e r e te s te d in the study: H yp oth esis 1: T h ere w ill be sig n ifica n t d iffe re n c e s betw een in tellig ib ility s c o r e s o f sen ten ces w ith secon d h a rm o n ic distortion and th o se w ith third h arm on ic d istortion . H ypothesis II: T h ere w ill be sig n ifica n t d iffe re n c e s betw een in tellig ib ility s c o r e s o f sen ten ces under conditions of d istortion v e r s u s n o n -d isto rtio n . H ypothesis III: T here w ill be sig n ifica n t d ifferen ces betw een in tellig ib ility s c o r e s o f sen ten ces obtained u sin g w id e band frequency r e sp o n se range and n arrow band freq u en cy r e sp o n se range. S ig n ific a n c e o f the P r o b le m K n ow led ge o f the p e r fo r m a n c e c h a r a c t e r is t ic s o f h e a r in g a id s is im p ortan t in s e le c tio n and eva lu a tio n . S u c c e s s fu l u s e o f a m p lifi cation by the h e a r in g im p a ir e d d ep en d s in p art upon th e in te llig ib ility and q u a lity of s p e e c h at th e output sta g e of the h e a r in g aid. D is t o r tion has b een h y p o th e siz e d a s on e u n d e sir a b le prod u ct o f low fid e lity a m p lif ie r s . T h e r e is no g e n e r a l c o n s e n su s am on g in v e s tig a to r s that d isto r tio n is u n d e sir a b le h o w e v e r , or that c e r ta in d isto r tio n p rod u cts a r e m o r e d e le te r io u s to s e n te n c e in te llig ib ility than o th e r s . It w a s the p u rp o se of th is study to in v e s tig a te the e ffe c ts o f th e s e fa c to r s on in te llig ib ility . CH APTER II REVIEW OF THE L IT E R A T U R E A u d io lo g ists involved in the evaluation o f h earin g aids for the hearing im p a ired have r elied g r ea tly on contribu tions from a llied field s in expanding their know led ge of e le c tr o -a c o u s tic s y s te m s . Only sin c e I960, how ever, has th ere been any c o n sisten t effort to in v e stig a te hearin g aid c h a r a c te r is tic s and th eir s y ste m a tic effects upon in tellig ib ility . Im p rovem en ts in h ea rin g aid s h ave not p a ra lleled the te c h n i c a l ad van ces in other v o ic e com m u n ication s s y s te m s su ch as radio and telep h on e although the h earin g aid is e s s e n tia l to m illio n s of peop le i f they a r e to function adequ ately in speaking and listen in g situ a tio n s. The u rg en t need to se a r c h for a n sw e r s to q u estion s relating to the p h y sio lo g y of hum an h ea rin g w a s given an additional im petus by tech n o lo g ica l ad van ces in in stru m en tation offerin g g r e a te r so p h is tication in m e a su rem en t. T h ese ad van ces help ed focus attention on 8 stu d ies of h ea rin g , and b ela ted ly , on stu d ies o f h ea rin g aids. By 1941 The B e ll T elep h on e L a b o r a to r ie s had provided m u ch o f the data on that w h ich con trib u ted to an e f f e c t iv e sp eech c o m m u n i cation s y s te m . ^ F le tc h e r and Stein b erg f ir s t in trod u ced the co n c ep t of an a rticu la tio n in d ex - a m eth od of m e a s u r in g the e ffe c tiv e n e ss of 2 a s p e e c h co m m u n ica tio n s s y s t e m - in 1929- T he A rticulation Index evalu ated a co m m u n ica tio n s y s t e m w ithout the e x p e n siv e and t im e con su m in g m eth ods p r e v io u s ly u sed . An in d ex o f the p e r fo r m a n c e of the s y s te m w h ich could be c a lcu la te d d ir e c tly fr o m known c h a r a c t e r is t ic s of the s y s te m w ould r ed u c e the tim e and c o s t of evaluation. F r en ch and Stein b erg e m b r a c ed th is idea and w e r e in terested in e x panding its u s e fu ln e s s by in trod u cin g ad d ition al data from r e la tio n - 3 sh ip s not a v a ila b le to F le tc h e r . F le tc h e r 's e m p h a sis w a s on the d e s ig n c r it e r ia for s y s t e m s op eratin g at low sig n a l le v e ls in quiet. F r e n c h and Steinberg e x panded p ertin en t a s p e c t s of th e c h a r a c t e r is t ic s o f sp eech and h e a r in g ^Leo L. B eran ek , "The D esig n o f S p e e c h C om m unication S y s te m s , " P r o c e e d in g s o f th e Institute o f R adio E n g in ee r s, XXXV (S ep tem ber, 1947), 8 8 0 -8 9 0 . 2 H arvey F le tc h e r and J. C. S tein b erg , "A rticulation T estin g M eth o d s," B e ll S y ste m T ec h n ic a l J o u r n a l, VIII (October, 1929), 8 0 6 -8 5 4 . 3 N. R. F r e n c h and J. C. S tein b erg, " F a cto rs G overning the In tellig ib ility of S p eech Sounds, " The Jou rn al o f the A cou stical S o c ie ty of A m e r ic a . XIX (January, 1947), 9 0 -1 1 9 . 10 and th e ir r e la tio n s to th e A r tic u la tio n Index for a s y s t e m o p era tin g w ith m o d e r a te n o is e l e v e l s . N ot u n til 1947 did F r e n c h and S tein b erg r ep o rt on the r e la tio n sh ip of th e s e and o th er e a r lie r data g o v ern in g 4 the in te llig ib ility o f s p e e c h so u n d s. The F r e n c h and S tein b erg co n trib u tio n to the A rticu la tio n Index c o n c ep t lie s in its a p p lic a b ility to lin e a r a m p lific a tio n d e v ic e s h avin g r e la t iv e ly flat, w id e band fr e q u e n c y r e s p o n s e ran ge. T h e re h as b een no e ffe c tiv e a p p lica tio n o f th e A rticu la tio n Index to low fid e lity a m p lify in g s y s t e m s su c h a s h e a r in g a id s. The v a lu e o f a p p ly ing th e A r tic u la tio n Index to h e a r in g aid function is q u e stio n a b le for two r e a so n s: F ir s t, h e a r in g a id s a r e , by c o m p a r is o n , low fid e lity s y s t e m s . S econ d ly, h ea rin g a id s a r e u tiliz e d for th e m o s t p art by in d ivid u als havin g en d -o rg a n le s io n s and sig n ific a n t lo s s o f s p e e c h in te llig ib ility . F r e n c h and S tein b erg em p lo y e d n o r m a l h e a r in g p e r so n s in e v o lv in g the A r tic u la tio n Index. K ry ter exten d ed th e p r a c tic a l a p p lica tio n o f the A r tic u la tio n Index in the ev alu ation o f s p e e c h c o m m u n ic a tio n s y s t e m s by p ro v id in g a m e a n s o f c a lc u la tin g s p e e c h in t e llig ib ility fro m the known sp e c tr u m 5 le v e ls o f s p e e c h and n o is e . H e a ls o d iv id ed the sp e c tr u m for s p e e c h 4 Ibid. , pp. 9 0 -1 1 9 . 5 K arl D. K ry ter, "M ethods fo r th e C a lcu la tio n and U s e o f the A rticu la tio n Index, " The Jou rn al o f th e A c o u s t ic a l S o c ie ty o f A m e r ic a . XXXIV (N o v em b er, 1962), 1 6 8 9 -1 6 9 7 . 11 into tw enty freq u en cy bands each contributing equally to sp e ec h in te l lig ib ility . Other in v e stig a to r s have sim p lified the m ethod by in tro - 6 ducing a m o r e e a s ily u tiliz ed set of com pu tation s. B r isk e y d e s c r ib e s a m ethod of arriv in g at a freq u en cy r e sp o n se index (FRI) allow ing for d irect c o m p a riso n s betw een h earin g aid s and th eir r e s p o n se c h a r a c te r is tic s elim in atin g rea l ear p e r fo r m an ce. He sta tes: T h erefo re, a quantitative num ber such as a sim p le FRI m e a s u rin g the optim um p e r fo r m a n c e of the in stru m en t excluding the ab n orm al ear p ro v id es a nu m ber w h ich w ill allow for the c o m p a r i son o f v a rio u s h earin g aids b a sed on a p red icted p e rfo rm a n ce as a com m u n ication s y ste m . This o b jectiv e index rating of the h earin g aid can then be u tiliz ed in the qu alitative evaluations u sin g s u b je c tiv e r e s p o n se of h earin g im p a ired p e r so n s. ^ The p r a c tic a l app lication of this sy ste m has not been d e te r m in ed . The m ethod u s e s tem p la tes show ing the 20 freq u en cy bands of K ryter su p e r im p o se d upon the frequency r e sp o n se cu rv e o f the h e a r ing aid. C alculation of the a r ea under the tem p la te cu rve g iv e s a nu m ber v a lu e for each of the tw enty freq u en cy bands and a s s ig n s a p ercen ta g e v a lu e b a sed on a c o u stic gain of the a m p lifie r at sp e cific bands. ^Gordon L. C luff and M ich ael C. P o lla ck , "A C om p arison o f S elected M ethods of D eterm in in g Sp eech In terferen ce C alcu lated by the A rticu lation Index, " The Journal of A uditory R e s e a r c h , IX (January, 1969), 8 1 -8 8 . 7 R ob ert J. B risk e y , W illia m H. G reenbaum and John C. S in clair, " F req u en cy R e sp o n se Index for Audio S y ste m s, " (unpub lish e d m a n u scr ip t);. 1 -1 1 . 12 H a rris and h is c o -w o r k e r s g iv e on e o f the c le a r e s t ex p o sitio n s on the confounding n atu re of the p r o b le m w ith w h ich w e a r e co n cern ed ; n a m ely , sp e e c h in te llig ib ility and the e le c tr o -a c o u s tic c h a r a c t e r is tic s o f h ea rin g aid s. If in fact one c lo s e ly e x a m in e s the op tim u m e le c t r o - a c o u s t ic c h a r a c t e r is tic s o f su c h c ir c u itr y for u se under ev ery d a y sp e e c h co n d itio n s, it is found that v e r y little p ertin en t data e x ist. W e do not know, for e x a m p le, w hat is the n a r r o w e s t a c ce p ta b le freq u en cy ran ge bandwidth; . . . W e do not know w h eth er the freq u en cy r e s p o n se should be flat or should exhibit a r isin g slo p e. We do not know the p e r ce n ta g e o f h a rm o n ic d isto r tio n at w hich sp e e c h in t e lli g ib ility b egin s to be a ffected . W e do n o t even h ave an idea as to w h ich o f m an y p o s s ib le m e a s u r e s of in term od u lation d isto rtio n should be looked into; as for tr a n s ie n t d isto rtio n , no c o m m e r c ia l lo u d sp ea k er is adequate even to begin the study o f that p robab ly c r u c ia l v a ria b le. T h ere a r e two d eep ly rooted d iffic u ltie s in attacking this field . F ir s t is the in te r r e la tio n am on g e le c tr o -a c o u s tic in d ex es. For ex a m p le, the freq u en cy r e s p o n s e c h a r a c t e r is tic m a y sh a rp ly in flu e n c e the h a rm o n ic d isto rtio n at certa in fr e q u e n c ie s. T his is p u r e ly p h y sica l phenom enon. It is d ifficu lt, often im p o s s ib le to v a r y a sin g le c h a r a c te r is tic w h ile le a v in g a ll o th er s w ith ou t change, . . . A seco n d d ifficu lty is that w h en two or m o r e typ es o f d is t o r tion, or n o is e in the b r o a d e st s e n s e , in the c ir c u it a r e added, the resu lta n t lo s s in in te llig ib ility is often m u ch g r e a te r than a s im p le addition w ould p r ed ict. F or ex a m p le , two types of n o is e , eith e r of w h ich w ould by it s e lf red u ce in te llig ib ility by on ly 5 p ercen t, m ay, w hen added, r ed u ce in te llig ib ility to 50 p e r c e n t or l e s s . T his is p a rtly p h y sic a l and p a rtly it is a function of how the h ea rin g m e c h a n ism co d es and d e c o d e s sp e ec h . Thus the r e la tiv e im p o rta n ce of a p a rticu la r type o f n o is e can be tru ly a s s e s s e d on ly by looking at its in ter a c tio n s a s w e ll a s its e ffe ct in iso la tio n . 8 g J. D. H a r r is, et al. , "The R elation b etw een S p eech In telli g ib ility and the E le c tr o -a c o u s tic C h a r a c te r is tic s o f Low F id e lity C ir cu itry , " T h e J o u ^ n a l^ f A u ^ it o r y R e s e a r c h ^ I (1 9 6 0 -1 9 6 1 ), 3 5 7 -3 8 0 . 13 B u rn ett c le a r ly d e fin e s p r o b le m s o f e le c t r o - a c o u s t ic r e s p o n s e s r e la t iv e to lim ita tio n s o f sta n d a rd d isto r tio n m e a s u r e s . Standard d is to r tio n m e a s u r e s u s e s p e c if ie d fr e q u e n c ie s . D is to r tio n p r o d u c ts, u sin g a c o m p le x s ig n a l s u c h a s s p e e c h , w i l l b e r e la t e d to d is to r tio n p r o d u cts ob tain ed w ith sta n d a rd p u re to n e s, but th ey w ill b e r e la te d in a m a n n e r d iffic u lt to d e s c r ib e o r m e a s u r e . H e m a in ta in s that: T h e re is no su c h thing a s the n o n lin e a r d is to r tio n o f a d e v ic e su c h a s a h e a r in g aid . R a th er, th e r e is a m e a s u r e d d is to r tio n w h ic h is d ep en d en t on the n a tu r e o f th e t e s t s ig n a l a s w e l l a s upon th e c h a r a c t e r is t ic s o f the d e v ic e b e in g te s te d . 9 W hen u s in g a c o m p le x s ig n a l s u c h a s s p e e c h , h a r m o n ic d i s to r tio n p ro d u cts g e n e r a t e in ter m o d u la tio n d is to r tio n p r o d u c ts. To h a v e one w ith o u t s o m e d e g r e e o f th e o th e r w o u ld b e e x t r e m e ly r a r e ju st a s it is d iffic u lt to g e n e r a te s e c o n d h a r m o n ic d is to r tio n w ith o u t at the s a m e t im e g e n e r a tin g h ig h e r o r d e r h a r m o n ic s . Thus it is i m p o s s ib le to e x a m in e th e e ffe c t s o f an y on e ty p e o f d isto r tio n in i s o l a - tion. W h ile it is p o s s ib le to m e a s u r e d is to r tio n u s in g sta n d a rd m e th o d s, th is m e a s u r e is r e s t r ic t e d to p u r e to n e s ig n a ls , and d o e s not show d is to r tio n o f a c o m p le x s ig n a l s u c h a s sp e e c h . 9 E dw in B u rn ett, "A N ew M ethod fo r th e M e a s u r e m e n t o f N o n lin e a r D is to r tio n U sin g a R an d om N o is e T e s t S ign al, " B u lle tin o f P r o s t h e t ic R e s e a r c h , B P R 1 0 -7 (Spring, 1967), 76. 14 T h erefore, one m ay ch o o se to m ake w h a tev er m e a su r e s he w is h e s u sin g pure ton es, and then r ela te th e s e to the subsequent m e a s u r e s of sp e ec h or oth er c o m p le x sig n a ls. H a rris and h is c o -w o r k e r s in v estig a ted m ean harm on ic d is tortion and sp eech d isc rim in a tio n and found c o r r e la tio n s betw een . 80 and . 88. ^ They concluded that h arm on ic d isto rtio n w as an im portant d e te r m in e r o f d iscrim in a tio n , but that it m u st ex ceed 20 p ercen t to d egread e sp eech . Interm odulation d isto rtio n and frequency r esp o n se range o f the aids w e r e sig n ifica n tly related to d iscrim in a tio n s c o r e s but w e r e r e la tiv e ly l e s s im p ortant than h arm on ic d istortion . H irsh and h is c o lle a g u e s in v estig a ted te s t relia b ility of h e a r ing aid e v a lu a t io n s .^ F ifteen su b jects evaluated four d ifferen t h e a r ing aids w ith differen t settin g s and failed to find any sign ifican t d iffe r en ces in sp eech d iscrim in a tio n in quiet or n o is e o v e r four d ifferent d ays. A co u stica l m e a s u r e s taken a fter the study w a s com p leted accounted for the lack of d iffe r e n c e s. They rep orted sign ifican t d if fe r e n c e s on d istortion and oth er m e a s u r e s taken on the aids, but th e se d ifferen ces did not co rresp o n d to d iffe r e n c e s in sp eech d is c r im ination s c o r e s found e a r lie r . * ^ H arris, loc. cit. 111. J. H irsh, I. Shore and K. Char an, ""Speech P ercep tion Through D ifferen t H earing A id s, " The Journal of the A co u stica l S o ciety of A m e rica , XXXI (August, 1959), 1584. 15 Z er lin , h o w e v e r , in trod u ced s e c o n d -o r d e r h a r m o n ic d is to r - 1 2 tion into taped P B w o r d lis t s u sin g a d isto r tio n g e n e r a to r . The d isto r tio n p rod u cts o f the g e n e r a to r w e r e r e c o r d e d on o n e tr a c k o f a two tra ck tape r e c o r d e r . The u n d isto r te d w o r d s w e r e r e c o r d e d on the oth er track . B y p layb ack , w h ile v a ry in g a m p litu d e o f the two tr a c k s , h e c o n tr o lle d the d e g r e e o f d isto r tio n . I n te llig ib ility w a s in v e s tig a te d a s a function o f fou r d e g r e e s of d isto r tio n - 0 p e r ce n t, 30 p e r c e n t, 50 p e r c e n t and 100 p e r c e n t. H is fin d in gs sh ow ed that p e o p le w ith n o r m a l h e a r in g and th o se w ith co n d u ctiv e l o s s e s w e r e a b le to w ith sta n d e ffe c ts o f d isto r tio n b e tter than th o se w ith s e n s o r i n e u r a l l o s s e s . I n te llig ib ility d e c r e a s e d a s th e s e v e r it y o f the s e n s o r i- n e u r a l l o s s in c r e a s e d . L ic k lid e r m a in ta in s that d isto r tio n is s u s p e c t a s a r e s p o n s ib le a g en t in d e te r io r a tio n o f s p e e c h p e r fo r m a n c e d e s p ite the fact that the h u m an ea r is r e m a r k a b ly r e s is t a n t to e ffe c ts o f m a n y ty p es o f d is - 13 to rtio n . P o lla c k c o m p a r e d the in te llig ib ility o f u n clip p ed s p e e c h w ith S tan ley Z e r lin , " E ffects o f H a rm o n ic In term o d u la tio n D is to rtio n on S p eech In te llig ib ility , " The Jou rn al of th e A c o u stic a l S o c ie ty of A m e r ic a , XXXII ( F eb ru a ry , I960), 1 5 0 1 -1 5 0 2 . 1 3 J. C. R. L ic k lid e r , " E ffects of A m p litu d e D isto r tio n Upon the In te llig ib ility o f S p eech , " The J ou rn al o f th e A c o u stic a l S o c ie ty o f A m e r ic a , XXIV (S ep tem b er, 1952), 5 3 8 -5 4 0 . 16 that of s e v e r e ly p eak -clipped sp e ec h as a function of the s ig n a l-to - n o is e ratio and as a function of the frequency band of the sp eech sig - 14 n al. He m ea su red sp eech in tellig ib ility using PB w ord s in a background of w hite n o is e in ord er to d eterm in e w heth er the su p e r io r ity of p eak -clip p ed sp eech at low s ig n a l-to -n o is e ratio and unclipped sp e ec h at high s ig n a l-to -n o is e ratio is a function o f the frequency band of the sp eech signal. He concluded: . . . for sp eech lim ited to a given frequency band, the in te lli g ib ility o f the unclipped sp eech , rela tiv e to that of the peak clipped sp eech , is a function o f the s ig n a l-to -n o is e ratio and is roughly independent of the frequency band em ployed. ^ Punch and M cConnel in vestigated the effects of in crea sin g in ten sity on the sp eech d iscrim in ation of eld erly su b jects. ^ T heir r e su lts indicated a reduction in sp eech in tellig ib ility in their subjects com p ared to sp eech in tellig ib ility in n o r m a ls, as in ten sity w as in c r e a s e d to 10 dB ste p s. They concluded that a n a rro w er in ten sity range e x ists for good sp eech d iscrim in a tio n in this population than in n o r m a ls. 14 Irwin P ollack , "On the E ffect of F requency and Am plitude D istortion on the In telligib ility of Speech in N oise, " The Journal of the A co u stica l S ociety of A m e r ic a , XXIV (Septem ber, 1952), 538-540. * * P* 540. 16 J e rr y L. Punch and F reem an M cConnel, "The Speech D is crim in ation Function of E ld erly P atien ts, " The Journal of A uditory R e se a r c h , IX (April, 1969), 159-166. 17 T3 output o output o output O F ig u r e 1. D ia g r a m s d e m o n str a tin g lin e a r and n o n -lin e a r a m p lific a tio n . (A) L in ea r a m p lifica tio n : Output am p litud e p ro p o rtio n al to input am p litu d e - no d isto r tio n . (B) N o n -lin e a r a m p lification : Output not p ro p o rtio n a l to input. T h is d e m o n str a te s s y m m e tr ic a l peak clip p in g r esu ltin g in odd h a rm o n ic d isto r tio n . (C) N o n -lin e a r a m p lifi cation: Output not p ro p o rtio n a l to input. T h is d e m o n str a te s a sy m - m e tic a l peak clip p in g r e s u ltin g in even h a rm o n ic d isto r tio n . 18 O pheim and F lo tto rp stu d ied a u r a l h a r m o n ic s in ad u lts w ith 1 7 n o r m a l and p a th o lo g ic a l h e a r in g . T h ey co n clu d ed that "a c o n n e c tion s e e m s to e x is t b etw een the r e c r u itm e n t p h en om en on and a b n o rm a l 18 h a r m o n ic th r e s h o ld s . 1 1 O pheim and F lo tto rp did not r e la te th eir fin dings to d is c r im in a tio n lo s s for s p e e c h . H uizin g and R ey n tjes d is c u s s e d the rela tio n b etw een r e c r u it - 19 m e n t and a u ra l d isto r tio n . In th eir opinion, d is c r im in a tio n l o s s for s p e e c h is d ir e c t ly r e la te d to r e c r u itm e n t a s the r e s p o n s ib le a g en t for g e n e ra tin g d isto r tio n . T hey d is c u s s e d th e im p o r ta n c e o f the lo u d n e ss function for s p e e c h in c a s e s o f p e r ce p tu a l d e a fn e s s , and s u g g e ste d g r e a t e r c o n s id e r a tio n be given to r e c r u itm e n t w hen c o m p e n sa tin g for a h e a r in g lo s s w ith h ea rin g a id s. By c o n str u c tin g a r tic u la tio n c u r v e s , th ey r ep o rted one c u r v e that r e la te d d ir e c t ly to the p r e s e n c e o f r e c r u itm e n t in p a th o lo g ic a l e a r s . In ad d ition to known c u r v e s: C -ty p e (con d u ctive) and P -ty p e (p er c ep tiv e ), H uizin g and R ey n tjes d e s c r ib e an R -ty p e (re cr u itm en t). 17 Odd O pheim and G ordon F lo tto rp , "The A u ral H a r m o n ics in N o r m a l and P a th o lo g ic a l H earin g," A c ta Q to la r y n g o lo g ic a , XLV (1955), 5 1 4 -5 3 0 . *^Ibid. , p. 524. 19 Henk C. H uizin g and J. A. R e y n tje s, " R ecru itm en t and S p ee c h D isc r im in a tio n L o ss , " L a r y n g o sc o p e , LXII (1952), 5 2 1 -5 2 6 . 19 E a rs w ith the R -type g e n e ra te an articu lation cu rv e that show s lo s s of in te llig ib ility w ith in crea sin g lo u d n ess. The lo s s o f in tellig ib ility on the cu r v e is held to be by the m e c h a n ism of "preponderating su b jec- 20 tiv e d isto r tio n due to p ath ological lo u d n ess function. " T hey a lso m aintain that su b jectiv e d isto rtio n ca u sed by r ec r u it m en t fa c to r s is different than h arm on ic d isto rtio n produced by h e a r ing a id s. T he authors p rop osed clipping or p a rtia l su p p ressio n by the a m p lifie r a s a m eans of red ucing the effects o f su b jectiv e d isto rtio n w ith the sta te m e n t that "... this m o v e s the cen ter o f in tellig ib ility to a part o f the frequency range in w hich su b jectiv e d isto rtio n can be 21 n e g le c te d . " In studying the e ffe c ts o f freq u en cy bandwidth upon sp eech d isc rim in a tio n , H arris and h is c o -w o r k e r s rep orted that n o rm a l h e a r ing su b jec ts, in co n trolled listen in g en viron m en ts, e x p e rie n c e little d ifficu lty in understanding s e n te n c e s fed through an 800 Hz low p a ss filter. T h is observation in te r e ste d them as n o rm a l h earin g p e r so n s s e e m to req u ire a m uch g r e a te r frequency bandwidth for u n d erstan d - 22 ing s p e e c h in n orm al en v iro n m en ta l surrou ndin gs in ev ery d a y life. 2 0 Ibid. , p. 523. ^ I b id . , p. 526. 22 J. Donal H a rris, H. L. H aines and C. K. M y ers, "The Im portance of Hearing at 3 Kc for U nderstanding Speeded Speech, " The L a ry n g o sc o p e , LXX (F eb ru ary, I960), 131 -1 4 6 . 20 T hey p r e se n te d d isto r te d sp e e c h to e a r s w ith a u d io m e tr ic p a t te r n s w h ich sim u la ted lo w -p a s s filter in g , i. e. , high freq u en cy h ea rin g l o s s e s . The d isto r tio n u tiliz e d w a s p rod u ced by a fa st ta lk er. He w a s a sta ff m e m b e r w ho h a b itu ally spoke at a v e r y fa st rate; 280 to 345 w o r d s per m in u te. The ta lk er rec o r d e d 100 se n te n c e s on tape and th is tape w a s p r e se n te d to th ree grou p s of su b je c ts. The fir s t group had l o s s e s b eginn ing at 4000 Hz, the seco n d group had l o s s e s b eg in ning at 3000 Hz and the third group had l o s s e s beginning at 2000 Hz. T hey con clu d ed that 4000 Hz w a s ir r e le v a n t to d isc r im in a tio n u n der th e s e co n d itio n s. In the seco n d group - l o s s e s beginn ing at 3000 Hz, th ey noted v e r y r e a l d istu rb a n ce in d isc r im in a tio n s c o r e s . 23 The m ean for this group w a s 6 9 .4 p ercen t. T hey con clu d ed that "a n o r m a l or n e a r n o r m a l a u d iogram at 3 Kc is e s s e n tia l for high 24 s e n te n c e in te llig ib ility if s t r e s s is put upon the sp e e c h sig n a l. " The effect o f the s t r e s s e d s p e e c h on the third group w a s g r e a t er d e c r e m e n ts in sp e e c h d isc rim in a tio n . T h e se in v e s tig a to r s r ejec te d the notion that freq u en cy d is t o r tion w a s r e s p o n s ib le and in stea d , p r e fe r r e d to sta te that 15 p e r c e n t o f ^ Ibid. , p. 1 36. 24 Ibid. , p. 142. 21 the c u e s for s e n te n c e in t e llig ib ilit y a r e fr e q u e n c y d ep en d en t upon 3 Kc reg io n . T h o m p so n and L a s s m a n u s e d 30 ad u lts in th e ir stu d y w ith h ig h fr e q u e n c y h e a r in g l o s s e s to t e s t s p e e c h d is c r im in a tio n u s in g tw o c o n - 25 d itio n s o f a m p lific a tio n . T he t e s t m e a s u r e s th ey u s e d to s e le c t su b je c ts w ith d is to r tio n w e r e : B e k e s y th r e sh o ld w id th , B e k e s y adap tation , B e k e s y lo u d n e ss tr a c k in g , SlSI and tone d e c a y t e s t s . O ne s y s t e m w a s r e la t iv e ly fla t, th e o th er a high fr e q u e n c y e m p h a sis s y s te m . T h om p son and L a s s m a n r e a s o n that s c o r e s for th e two s y s t e m s w ou ld b e r e la te d to the am ou n t o f d isto r tio n in th e a u d ito ry s y s t e m o f th e ir s u b je c ts , s in c e s y s t e m s w ith g r e a t e r d is to r tio n w o u ld be m o r e s u s c e p tib le to b e in g o v e r d r iv e n by h igh fr e q u e n c y a m p lific a tio n . T h e se in v e s tig a to r s h y p o th e s iz e d s u b je c ts w ith le a s t d is to r tio n w o u ld b e a b le to d is c r im in a t e s p e e c h b e tte r th rou gh th e high fr e q u e n c y e m p h a sis s y s t e m . R e s u lts fa ile d to in d ic a te any h igh d e g r e e o f s i g n if ic a n c e for d if f e r e n c e s b e tw e e n th e two s y s t e m s , though th e r e w a s s o m e e v id e n c e fo r s lig h tly b e tt e r d is c r im in a tio n s c o r e s for th e h ig h 26 fr e q u e n c y e m p h a s is s y s t e m . 25 G a ry T h o m p so n and F ra n k L a ss m a n , " R e la tio n sh ip o f A u d ito ry D isto r tio n T e s t R e s u lts to S p eech D is c r im in a tio n th ro u g h F la t v s . S e le c t iv e A m p lify in g S y s t e m s , " J o u rn a l o f S p eech and H e a r ing R e s e a r c h , XII (S e p te m b e r , 1969), 5 9 4 -6 0 5 . o L Ibid. , p. 604. 22 J e r g e r , in. an extended s e r i e s of ex p erim en ta l in v estig a tio n s on d isto rtio n , d ir e c te d h is e ffo r ts tow ard finding the extent to w hich the p h y sica l p erfo rm a n ce c h a r a c t e r is tic s of h earin g aid s including d isto rtio n , a re im portant to the u s e r ' s ability to un d erstan d sp eech . He sought a n sw er s to the fo llo w in g fiv e questions: F ir s t , is it p o ssib le to find a behavioral tech n iq u e that w ill d ifferen tiate am on g h ea rin g a id s ? S econd, a re d iffe r e n c e s am on g a id s, as m e a s u r e d by su ch a tech n iq u e, la r g e r , as la r g e , or sm a lle r for h ard of h earin g lis t e n e r s than for n orm al lis t e n e r s ? T hird, is th e r e any in te r a c tio n betw een h ea rin g aid s and type of h ea rin g lo s s ? In other w o r d s , are certain a id s b e st for p atien ts w ith one type of l o s s , and o th er aids better for other ty p es of l o s s , or is th e b e s t aid for anyone the b e st aid for e v er y o n e ? F ou rth , what is the o p tim a l behavioral tech n iq u e for d iffe r entiating am ong h earin g a id s ? What com bination of sig n a l input and ex p erim en ta l ta sk b e s t rank ord ers aids in a valid and r e lia b le m an ner w ith m in im a l in t e r -s u b je c t varian ce, in te r m s of the h e a r ing aid u s e r 's a b ility to u n d ersta n d sp eech ? F ifth , how m u ch of a p h y sic a l difference m a k e s a b eh avioral d iffe r e n c e ? In other w o r d s, at what point on th e continuum of any p h y sica l c h a r a c te r istic of h e a r in g a id s, does th e b eh a v io ra l index r e f le c t a change fro m r e la t iv e ly good or r e la tiv e ly poor "usa b ility" ? 27 In an effort to an sw er h is f ir s t question reg a rd in g a t e s t te c h nique that w ill d ifferen tiate a m o n g hearing aid s, J e rg e r s e le c te d 27 Ja m es J e r g e r , " B eh a v io ra l C orrelates of H earin g Aid P e r fo r m a n c e ," BuHntin_^f_Proathnti£S_Re£eanch, B P R 10-7 (Spring, 1967), 6 2 -7 5 . 23 th r e e d iffe r e n t h e a r in g a id s; (A) a v e r y g o o d a id , (B) an a v e r a g e aid , and (C) a v e r y p oor a id . H e a rin g a id A w a s d e s c r ib e d a s h avin g a sm o o th fr e q u e n c y r e s p o n s e and m in im a l d is to r tio n . H ea rin g a id B w as c h a r a c t e r iz e d a s h a v in g a p ea k ed fr e q u e n c y r e s p o n s e and m o d e r ate d is to r tio n . H earin g aid C w a s d e s c r ib e d as havin g c o n s id e r a b le d is to r tio n and a poor fr e q u e n c y r e s p o n s e . T h e s e th r e e a id s h ad su b sta n tia l d if f e r e n c e s . F o r th e t e s t m a t e r ia l to d iffe r e n tia te am on g the a id s , J e r g e r c h o se th e P A L - 8 s e n te n c e in t e llig ib ility t e s t b e c a u s e e a r lie r e x p e r ie n c e had sh ow n p h o n e tic a lly b a la n ced w o r d s did not d e lin e a te c le a r ly , d iffe r e n c e s am o n g a id s of d ifferin g a c o u s tic c h a r a c t e r i s t i c s . T ape r e c o r d e d s e n t e n c e s f r o m P A L - 8 l i s t s w e r e p layed thr.ough th e th re e d ifferen t h e a r in g a id s and th en r e - r e c o r d e d on ta p e . T h e se s e n t e n c e s , a s m o d ifie d by c h a r a c t e r is t ic s o f the th r e e a id s , w e r e th en p la y e d to a group of s ix n o r m a l l i s t e n e r s . R e su lts sh o w ed the a id s ran k ed in o r d e r a c c o r d in g to th e ir c h a r a c t e r is t ic s . H ea rin g aid A , th e v e r y good a id , a lw a y s y ie ld e d th e h ig h e s t d is c r im in a tio n s c o r e . H e a rin g a id B , the a v e r a g e a id , ranked n ex t and h e a r in g aid C, the v e r y p oor a id , a lw a y s y ie ld e d th e p o o r e s t d is c r im in a t io n . T h e sa m e r e c o r d e d m a t e r ia ls w e r e n ex t p r e s e n te d to a group of s ix p a tien ts w ith s e n s or i- n e u r a l l o s s e s in o rd er to a n sw e r th e sec o n d q u estio n : a r e d if fe r e n c e s a m o n g a id s m e a s u r e d in th is m a n n er p r e se n t fo r h ard of h e a r in g li s t e n e r s ? 24 The r e s u lt s w e re e s s e n tia lly id en tica l in that the th r e e aids w e r e a gain ranked in the sa m e ord er. F o r the th ird q u estion regard in g in tera ctio n betw een h ea rin g a id s of d ifferin g c h a r a c te r is tic s and h ea rin g lo s s e s of differin g ch ar a c t e r is t ic s , the r eco rd ed sen te n c es w e re played to a group of 36 h e a r ing im p a ired ind ividuals who " rep resen ted e v e r y co n ceiv a b le type and d e g r e e of h earin g lo s s for w hich a w ea ra b le h earin g aid w ould be con- 28 sid e r e d ap p rop riate. " R esu lts show ed th at su b jects w ithin th is group rank o r d ered the aids in the sa m e m an n er a s th e other tw o groups . H earin g aid A c o n siste n tly y ield ed h igh er d isc rim in a tio n s c o r e s than h ea rin g aid B or h ea rin g aid C r e g a r d le s s of the type or d e g r ee of h ea rin g l o s s . D ata co n cern in g the d e g r ee or type of d isto rtio n p r e s ent in the aids w as not given. In a n sw er to h is fourth q u estio n , J e rg e r d eterm in ed the opti m a l b eh a v io ra l technique for d ifferen tia tin g am ong h earin g a id s, w a s a t e s t involving in term od u lation d isto rtio n . He r eco rd ed in term od u la- tion d isto r tio n products of two fr e q u e n c ie s fed through the h earin g a id s. A nother tape of th e tw o fr e q u e n c ie s w a s u se d a s the c le a n s ig n al. The su b jects only ta sk w a s to identify the clea n signal as h eard f ir s t or th e d isto rted sig n a l a s h ea rd f ir s t . B oth w e r e p r esen ted in random ord er. 28 Ib id . , p. 66. 25 R e su lts again ranked the a id s in A, B, C o r d e r . The b e st aid, the m in im a l d isto r tio n aid, w a s d iffic u lt to d istin g u ish fr o m the clean sig n a l. T he aid w ith c o n s id e r a b le d isto r tio n , aid C, w a s e a s ie s t to id en tify. The f ir s t four q u e stio n s p o se d by J e r g e r in h is stu d y o f h e a r ing a id s w e r e r ep o rted in tw e lv e p a g e s . T he r e s u lt s o f h is study for the fifth q u estio n - how m u ch o f a p h y sic a l d iffe r e n c e m a k e s a b eh av io r a l d iffe r e n c e - e n c o m p a s s e d a total o f fo rty p a g e s . T his fifth stud y w a s c o n c e r n e d in d e ta il w ith "the r ela tio n sh ip b etw een s p e e c h u n d ersta n d in g and the e le c t r o - a c o u s t ic p a r a m e te r s of: (A) freq u en cy r e s p o n s e , (B) e ffe c tiv e bandw idths and (C) h arm on ic 29 d isto r tio n . " F r e q u e n c y r e s p o n s e c u r v e s fo r th e s e a id s w e r e su p p lied by the N ation al B u rea u o f S tan d ard s. The c u r v e s w e r e r e p r e s e n ta tiv e of the v a r ia tio n s to b e found in any la r g e group o f c o m m e r c ia l h e a r in g aids and in clu d ed w id e and n a r r o w fr e q u e n c y r a n g e s, fla t and slopin g c u r v e s , and sm o o th and ja g g ed c u r v e s . The e ffe c tiv e bandw idths w e r e ob tained fro m m e a s u r e s of the r e s p o n s e c u r v e s u sin g two d iffe r e n t m eth o d s; th o se o f th e U nited 29 J a m e s J e r g e r and J a m e s T h elin , " E ffects o f E le c t r o a c o u s tic C h a r a c te r is tic s o f H ea rin g A id s on S p eech U n d erstan d in g, " B u lletin of P r o s th e tic s R e se a r c h , B P R 1 0 -1 0 (F a ll, 19680, 159-197. 26 States of A m e r ic a Standards Institute (USASI) and the H ouston Sp eech and H earin g C enter (HSHC). The USASI m eth od a v e r a g e s the a c o u stic gain at 500, 1000 and 2000 Hz and d raw s a lin e h o rizo n ta lly a c r o s s the curve at a point 15 d e cib els b elow the a v e ra g e obtained. T he points at w hich the lin e in te r s e c ts the cu rve at eith e r end d efin es the effectiv e bandwith. The HSHC m ethod u s e s a lin e in te r se c tin g the r e sp o n se curve 10 d e c ib e ls b elow the h ig h est point on the c u rv e. The effe ctiv e d ifferen ce b e tw een the tw o m eth od s is the USASI m eth od y ie ld s sub- 30 stan tially g r ea ter m e a su r e d bandwidths than the HSHC m ethod. H arm on ic d isto rtio n w as m e a su r e d using th ree d ifferen t m e th o d s ; th o se em p lo y ed by N ational B u reau of Standards (NBS), the 31 S -3 -X -4 8 and HSHC. A ll th ree m eth od s y ie ld e d d ifferen t d e g r e e s of h arm on ic d isto rtio n for e v er y in stru m en t m e a su r e d . Synthetic Sen ten ce Identification (SSI) te s t s w e re reco rd ed through ea ch of tw en ty-on e h ea rin g aids; ten p o s t-a u r ic u la r , ten body type and one ey e g la s s e s m od el; and p r e se n te d to fiv e n orm al lis te n e r s . The t e s t r e s u lts w e re c o r r e la te d w ith the p r e v io u sly obtained m e a s u r e s of bandwidth and h a rm o n ic d isto r tio n of the s e v e r a l h earin g a id s. By both m eth od s of m e a su r in g bandwidth, the c o r r e la tio n of the SSI te s ts w ith bandwidth w as n e g a tiv e . R eex a m in in g th eir data for 30 Ibid. , p. 185. 31 The S -3 -X -4 8 is the n o m en cla tu re for a ten ta tiv e m ethod d evelop ed by USASI. 27 c lu e s to the r e a s o n s for th is u n ex p ec te d fin din g, J e r g e r and T h e lin r e p o r t the SSI m a t e r ia ls a r e w e ig h te d w ith low freq u en cy in fo r m a tio n and th e r e fo r e , r e s p o n s e b e lo w 1000 H z is the c r it ic a l ra n g e. T h u s, w h en the ra n g e a b o v e 1000 H z w a s c o r r e la te d w ith the su b jec t t e s t s c o r e s , the c o r r e la tio n w a s n e g a tiv e . H o w e v er , w h en the s a m e w a s done for the r a n g e b e lo w 1000 H z, the c o r r e la tio n w ith bandw idth w a s p o s itiv e . A n oth er u n ex p ec te d r e s u lt w a s ob tain ed w h en the c o r r e la tio n b e tw e e n h a r m o n ic d is to r tio n and SSI s c o r e s w a s e x a m in ed . A id s w ith the le a s t am ou n t o f d is to r tio n w e r e the a id s that g a v e p o o r e s t s c o r e s ! T h is w a s tr u e no m a tter w h ic h o f the th re e m eth o d s th ey em p lo y e d . T h e s e s a m e c o n c lu s io n s w e r e r e a c h e d w h en the e x p e r im e n t w a s e x tended to h e a r in g im p a ir e d lis t e n e r s . S p ea k s, J e r g e r and J e r g e r rep o rted , h o w e v e r, that the SSI s c o r e s do not r e f le c t n e c e s s a r ily the nu m ber of w o r d s r e c o g n iz e d in 32 the sy n th etic se n te n c e t e s t . In fa ct, the sy n th etic s e n te n c e s m ay b e c o r r e c t ly id e n tifie d w ith o u t havin g to u n d ersta n d an y of the w o r d s in the s e n te n c e . T h e w o r k can b e id e n tifie d by p o sitio n , len g th of u t t e r a n c e s of s o m e w o r d s or b y fe a tu r e s p e c u lia r to the s p e a k e r s rh y th m and in fle c tio n s . T h u s, th e r e s u lt s u sin g SSI m a y be r e la te d m o r e to 32 C h a r le s S p ea k s, J a m e s J e r g e r and S u san J e r g e r , " P e r fo r m a n c e In ten sity C h a r a c te r is tic s of S yn th etic S e n te n c e s, " J o u rn a l of S p eech an d H ea rin g R e s e a r c h , IX (June, 1966), 3 0 5 -3 1 2 . 28 effects p ecu lia r to the SSI m a te r ia l than to d istortion . It s e e m s apparent that distortion g e n e r a lly is r e sp o n sib le for the d eterio ra tio n of sp e e c h in tellig ib ility in m any in sta n ce s. The p o s s ib ility e x ists that fa cto rs not y et fully u n d erstood a ls o m ay be sig n ifica n t con trib u tors to the d eterio ra tio n o f sp eech in tellig ib ility . C H A PT E R III M ETHOD T his e x p e r im e n t w a s d e sig n e d to in v e stig a te the e ffe c ts of d isto r tio n on in tellig ib ility . Su bjects w e r e v o lu n te e r s w ith known s e n s o r i-n e u r a l l o s s e s . F iv e r e c o r d e d s e n te n c e in te llig ib ility te s t s w e r e a d m in iste r e d to ea ch o f th irty su b jec ts. One te st w a s u n d is torted, four w e r e d isto r te d w ith the in se r tio n o f d isto rtio n g e n e r a to r into the reco rd in g s y ste m . Two o f the d isto r te d se n te n c e te s ts u se d seco n d h a rm o n ic d isto rtio n and two u se d third h a rm o n ic d isto rtio n . A dd itionally, a ll o f the fiv e s e n te n c e te s t s w e r e filte r e d to red u ce the freq u en cy r e s p o n se range. Thus, each su b ject r e c e iv e d one u n d is to rted se n te n c e te s t fir st, follow ed by one w ith seco n d h a rm o n ic d isto rtio n and a w id e freq u en cy r e s p o n s e ran ge, one w ith seco n d h a r m on ic d isto r tio n and a n arrow freq u en cy ran ge, one w ith third h a r m o n ic d isto r tio n and a w id e freq u en cy r e s p o n s e ran ge and one w ith th ird h a rm o n ic d isto rtio n and a n a rro w freq u en cy r e s p o n s e ran ge. The w id e and n arrow freq u en cy r e s p o n s e ra n g es w e r e c h o sen to a p p ro x im a te the r e s p o n se s a v a ila b le in w e a r a b le h ea rin g a id s. 29 30 Second and third h arm on ic distortion w e r e a lso ch osen to approxim ate the d istortion s p re se n t in w ea ra b le hearing aids n o rm a lly availab le to p erso n s w ith se n so r i-n e u r a l h earin g lo s s e s . It w a s h yp othesized that significan t d ifferen ces in d iscrim in a tio n w ould be p resen t b e tw een the variou s com binations of d istortion and frequency resp o n se range rep resen ted . Subjects The te st population co n sisted of th irty su bjects, th irteen m a le and seven teen fem ale, w ith m e d ic a lly diagnosed s e n so r i-n e u r a l type o f h earin g lo s s . A ges ranged from 18 to 83 y e a r s , w ith a m ean of 59 y e a rs. Subjects w e r e v o lu n teers s e le c te d from the routine c a s e load of the audiology departm en t of the San Diego Speech and Hearing C enter. Each w a s req uired to have had an o to lo g ica l exam ination w ithin the past s ix m onths, along w ith a h isto ry , etiology and d iag n o s is of type of h earin g lo s s . Subjects w ith a h isto r y of recen t upper r esp ir a to r y illn e ss w e r e excluded. They w e r e required to m eet the follow ing aud iom etric criteria : (1) bone conduction th resh old s r e v e a l ing no m o re than a 5 d ecib el d ifferen ce from a ir conduction th resh old s for the freq u en cies 250 Hz through 4000 Hz, (2) no le s s than a 20 d e c i b el lo ss re: ISO -1964 for the sa m e freq u en cies for air and bone 31 condu ction, (3) s p e e c h rec e p tio n th re sh o ld s not l e s s than 25 d e c ib e ls , (4) s p e e c h d isc r im in a tio n s c o r e s not le s s than 50 p e r c e n t as m e a s u red by p h o n e tic a lly b a la n ced w o rd s at the m o s t c o m fo r ta b le lo u d n ess le v e l (M CL). lh o r d e r to e lim in a te the p o o r e st r e a d e r s , all su b jects w e r e r eq u ired to p a ss G ray's ora l reading test at the fifth g ra d e le v e l and w e r e r eq u ired to h a v e g e n e r a l A m e rica n sp eech . M a teria ls The te st se n te n c e s w e r e r ec o r d e d by an e x p e r ie n c e d m a le sp e a k e r on S co tch 1 m il a c e ta te m a g n etic r eco rd in g tape. F iv e s e p a r a te fo r m s o f a m u ltip le fo r c e d -c h o ic e in te llig ib ility t e s t c o n str u c ted by J e r g e r fro m P s y c h o -A c o u s tic L abs A u d itory T e s t #8 2 w e r e u s e d . E ach form c o n s is t e d o f fifteen s e n te n c e s . E ach s e n te n c e w a s a sin g le q u estion or com m an d a c co m p a n ied b y four p o s s ib le r e s p o n s e c h o ic e s . (See A ppendix A for t e s t fo r m s. ) The s e n te n c e s a r e str u c tu r ed in a m a n n er su ch that the su b ject m u st 1W. S. G ray, S tan dardized O ral R eading P a ra g ra p h s (B lo o m ington, Illin o is P u b lic S ch ool P u b lish in g Co. , 1957), p. 1 -4 . 2 J a m e s J e r g e r , C h a rles Sp eak s and C arolyn M alm qu ist, "H earing A id P e r fo r m a n c e and H earin g Aid S e lectio n , " Journal o f S p eech and H earin g D is o r d e r s , LX (M arch, 1966), 1 3 5 -1 4 9 . 32 hear m o st or a ll of the k e y w o r d s in o rd er to ch o o se the c o r r e c t an sw er. The following a r e sa m p le questions: Q. Books a r e printed on a : A. co m p a ss printing p r e ss author feet Q. P e a r ls a r e found in: A. o y ste r s d o r m ito rie s h air books Q. U nderline the w ord beginning w ith the letter P: A. ta ste letter p ear lin e Each subject w as given five sep a ra te sh e ets of paper w ith the a n sw ers for each test printed on the paper in ord er of p resentation from one to fifteen. Subjects w e r e provided a clip board and a p en cil for m arking their a n sw er s on the sh eet following p resen tation of the tape reco rd ed qu estion s through the earphone. P r e lim in a ry in vestigation during the pilot study has shown that in terv a ls longer than five secon d s betw een sen ten ces w e re disturbing to so m e subjects and that five second in terv a ls provided su fficien t tim e for subjects to s e le c t and m ark th eir an sw er. Each sen ten ce required no m o r e than 8 secon d s reading tim e. Subjects w e r e p r e sented four p ra ctice ite m s b efore p roceed in g w ith the te st. Each te st w as p reced ed by an alerting statem en t, "A re you read y?" 33 E quipm ent and R ecord in g P r o c ed u r e T e st se n te n c e s w e r e r e c o r d e d in itia lly in an u n d isto rted c o n d i tion w ith lull freq u en cy r e s p o n s e range on Scotch 1 m il a c e ta te tape at 7 - 1 / 2 IPS on an A m p ex m o d e l 1270 tape r e c o r d e r in an LAC 1200 s e r i e s sound c h a m b er. An A lliso n m o d el 22 r e s e a r c h a u d io m eter w a s em p lo y ed in o rd e r to u t iliz e the VU m e te r for m o n ito rin g p u rp o se s. The A m p ex tape r e c o r d e r w a s rep o rted to h a v e a freq u en cy r e s p o n se of plus or m in u s 2 dB from 50 to 12, 000 Hz at 7 - 1 / 2 IPS, The r e co rd ed s e n te n c e s w e r e then p layed through a h a rm o n ic d isto rtio n g e n era to r cap ab le of p rodu cin g a contin uous flat le v e l o f eith er seco n d h a rm o n ic d isto rtio n or th ird h a rm o n ic d isto r tio n throughout the range 3 from 50 Hz to 8000 H z. F ig u r e 3 sh ow s a sim p lifie d sc h e m a tic of this equipm ent. The output o f the h a rm o n ic d isto rtio n g e n e ra to r w a s fed to an A lliso n filte r , m o d e l 25, and r ec o r d e d in its d isto r te d and filte r e d sta te on a V iking tap e r e c o r d e r , m o d el 87, in co rp o ra ted as a com p on en t o f the A lliso n m o d el 22 a u d io m eter. F ig u re 2 show s a b lock d iagram o f th is equipm ent. C alibration o f the d isto r tio n g e n e ra to r w a s a c c o m p lish e d by g en era tin g a p u re tone sig n a l from a B ru el and K jaer audio freq u en cy 3 The h a rm o n ic d isto r tio n g e n e r a to r w a s co n str u c ted as an e x p e rim en ta l apparatus by the H earin g Aid D iv isio n o f Z enith Radio C orp oration and loaned for this study by John S in cla ir, C h ief E n g in eer, H earin g A id D iv isio n . SET DISTORTION GAIN POWER LEVEL AMPLIFIER AMPLIFIER OUTPUT INPUT ODD HARMONIC EVEN HARMONIC F igure 2. Sim plified sch em atic diagram of Zenith distortion generator. V iking Tape R ecorder A m pex Tape R ecorder A llison Filter Zenith D istortion Generator Reproducing Recording Figure 3. Block diagram of apparatus u sed to produce and record distorted te s t tap es. 36 s p e c tr o m e te r type 1212 and fe e d in g it through th e d isto r tio n gen erator. A tten u ator se ttin g s on th e d is to r tio n g e n e ra to r w e r e ad ju sted and set for 30 p e r c e n t h a rm o n ic d isto r tio n . T he d isto r tio n g en era to r output w a s r e c o r d e d for v is u a l d isp la y of th e h a r m o n ic d isto r tio n of the pure ton e and rec o r d e d on a B r u e l and K jaer graphic le v e l r e c o r d e r type 2305. F ig u r e 4 sh ow s the output of the d isto r tio n gen era to r s e t for a fla t freq u en cy r e s p o n s e and fo r 30 p e r ce n t seco n d h a rm o n ic d is to r tio n . F ig u r e 5 show s the output of th e g e n e ra to r w hen s e t fo r 30 p e r cen t th ird h a rm o n ic d isto r tio n . T he u p p e rm o st lin e r e c o r d e d on the g ra p h p ap er show s the r e l a tiv e ly fla t freq u en cy r e s p o n s e of the s y s t e m . The freq u en cy r e sp o n se exten d s fr o m 100 Hz throu gh 2000 Hz b e fo r e any sig n ifica n t deviation is ap p aren t. At th is point it b e g in s to drop s lo w ly u n til it r e a c h e s a point 3 dB down fr o m 2000 Hz at 5000 H z. The sec o n d h a rm o n ic d is to r tio n is d isp la y ed as a s e r i e s of c u r v e s b elow the freq u en cy r e s p o n se . The p eak s and v a lle y s of th e s e c u r v e s r e p r e s e n t the sk ir ts of th e th ird octave band a n a ly z e r , a B ru el and K jaer type 2112, E a ch one th ird octa v e of th e a n a ly z e r filte r is a u to m a tic a lly sw itch ed to the n ext filte r p o s itio n a s the a n a ly z e r tr a c k s and r e c o r d s the in te n sity of the h a rm o n ic d isto r tio n b ein g a n a ly z e d . The p ercen t h a r m o n ic d isto r tio n is m e a s u r e d r e la tiv e to the n u m ber of d e c ib e ls 37 30H 5 umn 20pl0 O'-O 100 500C 200 Hz 1000 2000 Hz 20 Hz 500 50 10 F ig u re 4. F req u en cy resp o n se and 30 percen t secon d h arm on ic d istortion cu rv es of the Zenith d istortion gen erator. A. F req u en cy resp o n se of the gen erator. B. Second harm onic d istortion m e a su r ed at third octave in ter v a ls. C. Line rep resen tin g 10 percen t third har m onic d istortion . r25 c(B -20 -15 Ho L0 200 Hz 500 1000 2000 Hz 500U F igure 5,. A. F requency r esp o n se of the gen erator. B. Third harm on ic distortion m e a su r ed at third octave in terv a ls. C. Line rep resen tin g 10 p ercen t second harm onic distortion . 38 b e tw e en the freq u en cy r e s p o n s e c u r v e and the peaks of th e d isto r tio n c u r v e . T h u s, if w e sta r t at 1000 Hz on the freq u en cy r e s p o n s e cu r v e and count ea ch d iv isio n down to the d isto r tio n cu rve a s 2 d e c ib e ls , w e find that the sep a ra tio n is a p p ro x im a te ly 10 d e c ib e ls . T en d e c i b e ls r e p r e s e n t a 30 p e r c e n t h a r m o n ic d isto rtio n . T he p e r c e n t d is to rtio n is ca lcu la te d by r e fe r r in g to a c o n v e r sio n ta b le su p p lied by the m a n u fa c tu r e r. The ta b les are d e r iv e d fr o m the m a th e m a tic a l r e la tio n s b etw een am p litud e of v o lta g e s p rod u ced by the fu n d am en tal f r e qu en cy and the h a r m o n ic s of the fu n d am en tal freq u en cy . F ig u r e 5 is the d isp la y r e c o r d e d w ith the g e n e r a to r s e t to p rod u ce th ird h a r m o n ic d isto r tio n . T he cu rves in fig u r e 5 occupy a p o sitio n on the graph paper that is lo w e r than the c u r v e s in fig u re 4 . T his sh ift is s im p ly a function of d iffe r e n t range s e ttin g s for th e grap h ic le v e l r e c o r d e r and the s p e c tr o m e te r and not a n a ctu a l le v e l ch an ge. T he r e la tiv e p o sitio n of the freq u en cy r e s p o n s e cu r v e is the im p ortan t point. The lo w e r m o s t c u r v e running th rou gh the sk ir ts of the d isto r tio n d isp la y in ea ch of the r ec o r d in g s r e p r e s e n t a p p ro x i m a te ly 10 p e r c e n t sec o n d h a r m o n ic d isto r tio n in fig u re 4 and a p p ro x i m a te ly 10 p e r c e n t th ird h a rm o n ic d is to r tio n in fig u re 5. T h is is b e c a u s e n o n -lin e a r ity , w h ile p ro d u cin g a p red om in an ce of one type of d isto r tio n , a ls o p ro d u ces at th e s a m e tim e , l e s s e r am o u n ts of other ty p e s of d isto r tio n . In the c a s e a t h an d , the p red om in an t d isto r tio n 39 or n o n -lin e a r ity in fig u re 4 is s e c o n d h a r m o n ic . T he s a m e o b s e r v a tion w o u ld a p p ly to th e c a s e of th e g e n e r a to r s e t in the th ird h a r m o n ic m o d e . T he fr e q u e n c y r e s p o n s e ra n g e of the se n te n c e m a te r ia l w a s r ed u c ed a fte r it w as r e c o r d e d and fe d th ro u g h th e d is to r tio n g e n e r a to r by p a s s in g it th rou gh the A llis o n f il t e r . The r o ll- o f f of the A llis o n f ilt e r is 30 d e c ib e ls p er o c ta v e . T hus fo r con d ition 1, the m a t e r ia l w a s u n d isto r te d and had a fr e q u e n c y r e s p o n s e ra n g e c o r r e sponding to that of m o s t good h e a r in g a id s; n a m e ly fr o m 210 Hz th rou gh 4 0 8 0 H z. F o r co n d itio n s 2 and 3, th e fr e q u e n c y r e s p o n s e ra n g e w a s the s a m e a s fo r co n d itio n 1, but w ith th e a d d itio n a l fa c to r s that co n d itio n 2 w a s r e c o r d e d w ith the d is to r tio n g e n e r a to r in the se c o n d h a r m o n ic m o d e and co n d itio n 3 w a s r e c o r d e d w ith the g e n e r a tor in the th ird h a r m o n ic m o d e . C on d ition s 4 and 5 r e q u ir e d a d d i tio n a l filte r in g to a c h ie v e a fr e q u e n c y r e s p o n s e ran ge fr o m 210 Hz th rou gh 2640 H z, c o r r e sp o n d in g to the fr e q u e n c y ra n g e of l e s s d e s ir ab le h e a r in g a id s . C on d ition s 4 and 5 w e r e s im ila r to co n d itio n s 2 and 3 in that th ey w e r e r e c o r d e d w ith the d is to r tio n g e n e r a to r in th e sec o n d and th ird h a r m o n ic m o d e s r e s p e c t iv e ly . T he c o ck ta il p a rty n o is e u s e d a s a b ack grou n d n o is e in the t e s t situ a tio n w a s r e c o r d e d on th e A m p e x r e c o r d e r a p p r o x im a te ly s ix m on th s e a r li e r at an a ctu a l p a r ty . It w a s r e c o r d e d fo r c lin ic a l u s e 40 a s a background n o is e in testin g d isc rim in a tio n for h earin g a id s. The p u rp ose in u sin g this n o is e w a s in keeping w ith the gen era l p u rp o se of the ex p erim en ta l te s t situation in providing conditions as c lo s e to the actual w ea rin g conditions e x p erien ced by the h ea rin g aid u s e r . V a r i ations in in ten sity o v e r tim e a r e shown in figu re 6. The r e la tiv e ly uniform le v e l shown w a s p r e se n t throughout the tim e period req uired for p resen tation of ea ch te s t tape. It w a s d e liv e r ed at a s ig n a l-to - n o is e ratio of 10 d e c ib e ls . C onventional e lec tr o n ic n o is e s co m m o n ly u se d as background n o ise , such as co m p lex or w h ite n o ise a re steady sta te and do not r e fle c t the u n p red ictab le v a ria tio n s ex p erien ced in actual listen in g situ a tio n s. F ig u res 7, 8, 9 and 10 show sa m p le s o f sp eech sp ectro g ra p h s 4 reco rd ed from each condition. The w ord "London" w a s a r b itr a r ily se le c te d for sp ectro g ra p h ic a n a ly sis and w a s the sa m e w ord in each c a s e . The sp ectro g ra p h of condition 1 is p r e se n ted on the bottom h a lf o f the page w ith each of the sp ectro g ra p h s o f conditions 2, 3, 4 and 5. Two am p litud e sec tio n r eco rd in g s a re shown su p erim p o sed on the sp ectro g ra p h s. The am p litud e sec tio n s show in ten sity along the h o rizo n ta l a x is and freq u en cy along the v e r t ic a l a x is. F req u en cy ca lib ra tio n m a rk s for the sp e ec h sp ectro g ra p h s Sp ectrograp h s w e r e provided by V oicep rin t L a b o ra to ries, S o m er v ille , New J e r s e y . Relative Intensity in dB 41 F ig u r e 6. B r u e l and K ja e r g r a p h ic l e v e l r e c o r d in g o f r e l a t iv e in t e n s it y v a r ia t io n s o f c o c k t a il p a r ty n o i s e a s a fu n c tio n o f t im e . {T o ta l tim e: 3 m in u te s ) F igure 7. Speech sp ectrograp h s com paring undistorted and d istorted conditions for the sa m e sp eech sounds. (A) Condition 1: undistorted. F req u en cy range 210-4080 Hz, (B) Condition 2: d is torted, 30 p ercen t second harm on ic. F requency range 210-4080 Hz. B _ 43 5000 Hz 4000 Hz 3000 Hz 2000 Hz 1000 Hz 4000 Hz 3000 Hz 2000 Hz 1000 Hz Brs & <•.«. F ig u re 8. Speech sp e ctro g r a p h s co m p a rin g u n d isto rted and d isto r te d con d ition s for the s a m e sp e e c h sou n d s. (A) C ondition 1: u n d isto rted . F req u en cy ran ge 2 1 0 -4 0 8 0 H z. (B) C ondition 3: d is torted , 30 p e r c e n t third h a rm o n ic. F req u en cy ran ge 2 1 0 -4 0 8 0 Hz. 44 5000 Hz 4000 Hz 3000 Hz 2000 Hz 1000 Hz 4000 Hz A 3000 Hz 2000 Hz 1000 Hz F ig u r e 9. S p eech s p e c tr o g r a p h s co m p a r in g u n d isto r te d and d isto r te d co n d itio n s for the s a m e s p e e c h sou n d s. (A) C ondition 1: u n d isto r te d . F r e q u e n c y ra n g e 2 1 0 -4 0 8 0 H z. (B) C ondition 4: d i s torted , 30 p e r c e n t s e c o n d h a r m o n ic . F req u e n c y ran ge 2 1 0 -2 6 4 0 Hz. 45 5000 Hz 4000 Hz 3000 Hz 2000 Hz 1000 Hz 4000 Hz 3000 Hz 2000 Hz 1000 Hz F igu re 10. Speech sp ectro g ra p h s com paring u n d istorted and d isto rted conditions for the sa m e sp e ec h sounds. (A) Condition 1: u n d istorted . F req u en cy range 2 1 0-4080 Hz. (B) Condition 5: d i s torted, 30 p ercen t third h a rm o n ic. F req u en cy range 21 0 -2 6 4 0 Hz. 46 a r e shown as dark h o r iz o n ta l m a r k s at the e x tr e m e Left hand edge of the rec o r d in g . The r ec o r d in g s w e r e taken in the n a rro w bandpass m o d e (40 H z) w h ich a llo w s the fu n d am en tals and h a r m o n ic s to show m o r e c le a r ly than w ould a w id e band s p e c tr o g r a m . In ten sity is shown as grad ation s in th e d a rk n ess of the s p e c tro g ra p h lin e s . The top m o s t ca lib ra tio n m a r k r e p r e s e n ts 6000 Hz. E ach su c ce e d in g m a rk is 1000 Hz lo w er. C lo s e exam in ation and c o m p a r iso n o f the d isto r te d and u n d is to rted con d ition s w ill r e v e a l d iffe r e n c e s in the s p e e c h sp e ctro g r a p h s. T h e se d iffe r e n c e s a r e rela ted to the p r e s e n c e or a b se n c e of d is t o r tion. T his can be s e e n c le a r ly in fig u re 7 for the r ec o r d e d bands beginn ing at the b ottom o f the e x tr e m e righ t hand m a rg in and p r o c e e d ing upw ard. The bands in (A), the u n d isto rted condition, show a m o r e r e g u la r and even p r o g r e s s io n than the bands in (B), the d isto rted condition. S im ila r d iffe r e n c e s can be s e e n in the p r o g r e s s io n of the bands n e a r the c e n te r of the r eco rd in g to the left o f the black a m p li tude se c tio n . T h e se d iffe r e n c e s r e p r e s e n t ch a n g es in h a rm o n ic freq u en cy str u c tu r e and ch a n g es and sh ifts in r e la tiv e in ten sity o f the h a r m o n ic str u c tu r e as a r e su lt o f d isto r tio n . In tellig ib ility o f sp e e c h 5 depend s on the p ercep tio n and reco g n itio n o f th e s e shifting p a ttern s. 5 N. R. F ren ch and J. C. S tein b erg , " F a cto rs G overning the In te llig ib ility o f S p eech Sound, " Journal o f the A c o u stic a l S o ciety of A m e r ic a , XIX (January, 1947), 9 0 -1 1 9 . 47 The dark am plitude section record in gs running through the cen ter o f each spectrograp h w e r e recorded in an effort to exam ine changes in in ten sity m o re c lo se ly . It w as not p o ssib le to obtain a m p litude sectio n s that corresp on d ed p r e c is e ly for the sa m e point in tim e. It can be seen h ow ever, e sp e c ia lly in figu res 9 and 10, that the am plitude sectio n for the d istorted conditions is h igh er v e r tic a lly than for the u n d istorted condition. This rep resen ts a sp read of h a r m on ics into the h igh er frequency region s as a resu lt of the p r e se n c e of distortion . P roced u re Routine sp eech and pure tone aud iom etric te sts w e r e a d m in is tered to su b ject-p a tien ts p rior to ad m in istration of the te st tap es. T hose patients who fulfilled the c r ite r ia as subjects w e r e inform ed of the nature of the exp erim en t and the tim e req u irem en t of 20 m in u tes. T hose a ssen tin g w e r e given the following ora l instruction s: You a re going to liste n to a s e r ie s of questions or com m an d s. T here w ill be n o ise in the background. L isten ca refu lly and try to an sw er by underlining your a n sw er on the an sw er sh eet. If you a re not su r e o f the an sw er, take a g u ess. Try to an sw er each question. The subject w as then shown four sam p le sen ten ces along w ith th eir p o ssib le a n sw ers on a sh eet of paper. The sen ten ces w e r e read aloud and the su b ject w as asked to un derline h is ch oice on the a n sw er sh eet. 48 Subjects w e re then ask ed if the task w a s u n derstood . No su b ject failed to understand the p ro ced u re. Subjects w ea rin g g la s s e s w e r e ask ed if lighting w a s adequate for them to s e e c le a r ly . All su b jects indicated lighting w a s adequate. G ray's O ral Reading T est for the fifth grade le v e l w a s given after the four sa m p le se n te n c e s had b een read. All su b jects p a ssed this test. Subjects then liste n e d to four m o r e p r a c tic e te st sen te n c es through the earphone on the b etter ear. This p ro ced u re w as d esign ed to give subjects p r a c tic e in handling the p en cil, clipboard, and m a r k ing their a n sw e r s and w e r e u se d by the ex p e rim en te r to e sta b lish com fort le v e ls o f liste n in g u sin g a m od ified m ethod of lim its. The following in stru ctio n s w e r e given to the subject: You a r e going to liste n to so m e p r a c tic e sen te n c es now. We w ant you to b e co m fo rta b le so lis te n and te ll m e if the sen te n c es a r e too loud or too so ft or ju st right. The subject in stru cted the e x p e rim en te r to r a is e or lo w er the le v e l until the m o st co m fo r ta b le le v e l w as ch osen . The te s t sen te n c es w e r e then d e liv e r e d to the su b jects at that le v e l judged to be m o st com fortable. The m o s t co m fortab le listen in g le v e l (MCL) w a s ch o sen for two rea so n s: (1 ) to avoid u n com fortab le or painful lou d n ess le v e ls w h ich m ight h a v e a ccru ed had an a rb itra ry p resen ta tio n le v e l been chosen, (2 ) to study d istortion under conditions approxim ating th ose o f n o r m a l u s e o f h e a r in g a id s. The o r d e r o f p r e se n ta tio n o f the four d is to r te d t e s t ta p es w a s c o u n te r -b a la n c e d to m in im iz e the d iffe r e n tia l e ffe c ts of co n d itio n s 2 th rou gh 5 .^ (See ta b le 1. ) C ond ition 1, the u n d isto r te d condition, w a s p r e se n te d f ir s t to a ll s u b je c ts . T h is a llo w e d su b jec ts to b e c o m e a cq u ain ted w ith p r o c e d u r e and e sta b lis h e d a b a s e lin e of p e r fo r m a n c e w ith w h ich to c o m p a r e p e r fo r m a n c e data fo r the d isto r te d co n d itio n s. A ll su b jec ts w e r e te s te d and m a t e r ia ls g a th ered p r e p a r a to r y to a n a ly s is of the data. B. J. W in er, S ta tis tic a l P r in c ip le s in E x p e r im e n ta l D e s ig n , (New York: M cG ra w -H ill B ook C om pany, Inc. , 1962), 2.41-248. Lbj< 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 TABLE 1 EXPERIM ENTAL DESIGN FOR ORDER OF PRESENTATION OF SENTENCE TESTS AND CONDITIONS T est Condition T est Condition T est Condition T est Condition T est 1 1 2 2 3 3 4 4 5 2 1 3 3 4 4 5 5 1 3 1 4 4 5 5 1 2 2 4 1 5 5 1 2 2 3 3 5 1 1 2 2 3 3 4 4 1 1 2 3 3 4 4 5 5 2 1 3 4 4 5 5 2 1 3 1 4 5 5 2 1 3 2 4 1 5 2 1 3 2 4 3 5 1 1 3 2 4 2 5 4 1 1 2 4 3 5 4 2 5 2 1 3 5 4 2 5 3 1 3 1 4 2 5 3 1 4 2 4 1 5 3 1 4 2 5 3 5 1 1 4 2 5 3 2 4 >je 16 17 18 19 20 21 22 23 24 25 26 27 28 29 4 5 2 3 4 5 2 3 4 5 2 3 4 5 TABLE 1 (continued) T est Condition T est Condition 1 1 2 5 2 1 3 2 3 1 4 3 4 1 5 4 5 1 1 5 11 2 2 2 1 3 3 3 1 4 4 4 1 5 5 5 1 1 2 1 1 2 3 2 1 3 4 3 1 4 5 4 1 5 2 5 1 1 3 T est Condition T est Condition 3 2 4 3 4 3 5 4 5 4 1 5 1 5 2 2 2 2 3 3 3 3 4 4 4 4 5 5 5 ' 5 1 2 1 2 2 3 2 3 3 4 3 4 4 5 4 5 5 2 5 2 1 3 1 3 2 4 2 4 3 5 C H A P T E R IV R E S U L T S To d e te r m in e the e ffe c t s o f h a r m o n ic d is to r tio n on s e n te n c e in t e llig ib ility , it w a s h y p o th e s iz e d that th e r e w o u ld be s ig n ific a n t d if f e r e n c e s b e tw e en in t e llig ib ilit y s c o r e s ob tain ed on the s a m e su b j e c t s u n d er tw o d iffe r e n t m o d e s o f h a r m o n ic d isto r tio n : (1 ) s e c o n d h a r m o n ic d is to r tio n and (2) th ird h a r m o n ic d is to r tio n . D uring th e e x p e r im e n t, s e n te n c e in t e llig ib ilit y s c o r r s w e r e m e a s u r e d and r e c o r d e d fo r fiv e s e p a r a te lis t e n in g c o n d itio n s. T h e se m e a s u r e m e n t s w e r e tr e a te d s t a t is t ic a lly in o r d e r to d is c o v e r w h e th e r d if f e r e n c e s e x is t e d a m o n g (1 ) s e c o n d h a r m o n ic d is to r tio n and th ird h a r m o n ic d is to r tio n , (2) d is to r te d and u n d is to r te d s e n te n c e s , (3) w id e band fr e q u e n c y r e s p o n s e and n a r r o w band fr e q u e n c y r e s p o n s e , and (4) an y o f the fiv e s e n te n c e t e s t s . S t a t is t ic a l P r o c e d u r e A tw o fa c to r a n a ly s is o f v a r ia n c e w a s p e r fo r m e d to d e t e r m in e w h e th e r th e r e w e r e n o n -c h a n c e v a r ia tio n s or in te r a c tio n s am on g 52 53 m ea n s. The data c o lle c te d w e r e co lla ted and sub jected to a two w ay a n a ly sis of v a r ia n c e. The design u tilized the follow ing factors: I. C onditions - five le v e ls; (1) u n d istorted, w id e freq u en cy range, (2 ) d isto rted , w id e frequency range w ith seco n d h arm on ic d istortion , (3) d istorted , w id e frequency range w ith third h arm on ic d istortion , (4) d isto rted , narrow freq u en cy range w ith sec o n d h arm on ic d is to r tion, (5 ) d isto rted , narrow frequency range w ith third h a rm o n ic d is tortion. II. T e sts - fiv e le v e ls; five fifteen item te sts d e r iv ed from PA L auditory te s t #8 . The design w a s arran ged to m in im iz e the d if feren tia l effects of te s ts two through five. The su m m a ry of a n a ly sis is p r esen ted in table 2. The . 05 p rob ab ility le v e l w a s u sed in this study for p u rp o ses of rejectin g the h y p o th esis. The m ean s c o r e s for the five trea tm en t conditions c o m puted by su m m in g a c r o s s te s ts is p resen ted g ra p h ica lly in figu re 1 1 . The r e su lts of the F te st a n a ly sis of the d iffe re n c e s am ong the m ea n s p r e se n te d in figu re 11 did not in d icate any sig n ifica n t d if fe r e n c e s at the . 05 le v e l of con fid en ce. F or a m o r e d eta iled a n a ly sis of the d iffe r e n c e s am ong th ese m ea n s, s ta tis tic a l c o m p a r iso n s w e r e com puted. ^ The s ta tis tic a l co m p a riso n is a m od ified t - t e s t p ro ced u re u tiliz e d to d ete r m in e sig n ifica n ce of d iffe r e n c e s b etw een c e ll m ea n s ^B. J. W iner, S ta tistica l P r in c ip le s in E x p erim en ta l D e s ig n , (New York: M cG raw -H ill Book Com pany, I n c . , 1962), p. 207. 54 T A B L E 2 ANALYSIS O F V A R IA N C E AM ONG M EANS S o u r c e Sum o f S q u ares df M ean Square F P T e s ts 32. 00 4 8 . 00 1 , 08 N. S. C ond itions 36. 00 4 8 . 00 1 . 2 2 N. S. In teraction 274. 00 16 17. 10 2. 32 . 1 0 E r r o r 923. 00 125 7. 38 - T otal 1265 149 - - - a fte r an F te s t is p e r fo r m e d . T h e se c a lc u la tio n s in d ica ted that the s e n te n c e in te llig ib ility s c o r e s obtained under con d ition 1 w e r e s ig n ific a n tly d ifferen t fro m the s e n te n c e in te llig ib ility s c o r e s obtained u n d e r any of the r e m a in ing co n d itio n s. D ata a ls o in d ica ted that the d if fe r e n c e s b etw een the in te llig ib ility s c o r e s o f c o n d itio n s 2 and 3 w e r e n ot s t a t is t ic a lly s i g n ific a n t at the . 05 le v e l o f c o n fid en ce . F u rth e r c o m p a r is o n s , h o w e v e r , in d ica ted sig n ific a n t d iffe r e n c e s at the . 05 le v e l of c o n fid en ce b etw een con d ition 2 on the on e hand and e ith e r con d ition 4 or c o n d i tion 5 on the o th er. T h e se s t a t is t ic a l c o m p a r is o n s a ls o in d icated sig n ific a n t d iffe r e n c e s b etw een con d itio n s 3 and 4 and con d ition s 3 and 5. F in a lly , the data did not in d ica te a n y sig n ific a n t d iffe r e n c e s b etw een the se n te n c e in te llig ib ility s c o r e s fo r co n d itio n s 4 and 5. 55 12.0 - *4 t fi O J 4a4 > , H-5- 15 ‘S o .£ 4 > U C 4 7 + j C 47 ( / ) § 11.0 - </3 u aJ O U c n Z < w S 10.5 5 4 2 3 CO N D ITIO N S F igure I I . Mean sc o r e s for the five treatm en t conditions. Condition 1: undistorted, w ide frequency range, Condition 2: 30 p e r cen t second harm onic distortion, frequency range 210-4080 Hz, Condition 3: 30 p ercen t third harm on ic d istortion , frequency range 210-4080 Hz, Condition 4: 30 p ercen t second harm on ic distortion, frequency range 210-2640 Hz, Condition 5: 30 percen t third h a r m on ic distortion , frequency range 210-2640 Hz. 56 The five sen te n c e in te llig ib ility s c o r e s com p u ted by su m m in g a c r o s s e x p erim en ta l con d ition s a r e p r e se n te d in table 3. F t e s t a n a ly sis of the d iffe r e n c e s am ong m ea n s p r e se n te d in tab le 3 ga v e a v a lu e o f 1. 08 w h ich w ith 4 and 125 d e g r e e s of freed o m w a s not found to be s t a t is t ic a lly sig n ifica n t at the . 05 le v e l o f c o n fid en ce. H ow ever, s ta tis tic a l c o m p a r iso n s, a m o d ified t_ te st, com pu ted on th e s e data did in d icate s o m e sig n ifica n t d iffe r e n c e s. T h e se c a lcu la tio n s in d icated that the m ean in te llig ib ility s c o r e s for t e s t 5 w e r e sig n ific a n tly lo w e r than the oth er m ea n s c o r e s on the rem ain in g t e s t s . One add ition al d iffe r e n c e w as found. That w a s b etw een t e s t 3 and te st 4 w ith t e s t 3 giving lo w er s c o r e s than t e s t 4. The m ean se n te n c e in te llig ib ility s c o r e s for th o se su b jects r e c e iv in g w id e and n a rro w freq u en cy bandwidths fu rth er subdivided by r e c e iv in g p red o m in a n tly secon d h arm on ic d isto rtio n and p r e d o m i nan tly third h a rm o n ic d isto rtio n a r e p r e se n te d in tab le 4. T A B L E 3 S E N T E N C E INTELLIG IBILITY SCORES FOR THE FIV E TEST AND CONDITIONS COM BINED T e sts 1 2 3 4 5 M ean Sp eech In te llig ib ility 1 1 .3 9 1 1 .4 1 1 0 .9 9 1 1 .7 7 1 0 .2 3 S c o r e s (% correct) 57 T A B L E 4 M E A N S E N T E N C E IN T E L L IG IB IL IT Y SC O R ES FOR W IDE A N D NARROW BANDW IDTH BY SECO ND A N D THIRD HARMONIC DISTORTION Bandw idth W id e N a rro w T otal S econ d H arm on ic D isto r tio n 11. 33 10. 67 1 1 . 00 T hird H arm on ic D isto rtio n ' 10. 07 10. 63 10. 85 T otal 1 1 . 20 10. 65 - ‘P e r c e n t c o r r e c t. F ro m th e m e a n s p r e s e n te d in tab le 4, it is ev id en t that th o se su b jec ts r e c e iv in g the w id e fr e q u e n c y bandw idth atta in ed h ig h er s e n te n c e in t e llig ib ility s c o r e s than w h en p r e se n te d s e n te n c e s w ith the n a rro w bandwidth. The m e a n s c o r e s com p u ted by co m b in in g se c o n d and th ird h a rm o n ic w e r e 11. 20 for the w id e band and 10. 65 for the n a rro w band con d ition . T he d iffe r e n c e s b etw een th e s e m e a n s w a s found to be s t a t is t ic a lly sig n ific a n t (t_ = 1. 85, d F = 28). T h is finding in d ic a te s that the n a rro w bandw idth p rod u ced lo w e r s e n te n c e in t e lli g ib ility s c o r e s than did the w id e bandwidth. F ro m the m e a n s s u m m a r iz e d in ta b le 4 it is a ls o evid en t that the s e n te n c e in t e llig ib ility s c o r e s o f th o se su b je c ts r e c e iv in g p r e d om in an tly sec o n d h a r m o n ic d isto r tio n a r e h ig h e r than the se n te n c e in te llig ib ility s c o r e s a c h ie v e d w h en th e su b je c ts r e c e iv e d the condition 58 w ith pred om in an tly third h a rm o n ic d isto rtio n . The m ean sp e ec h in tellig ib ility s c o r e s for the seco n d h arm on ic d istortion condition com puted by su m m in g a c r o s s bandwidths w a s 1 1 . 00 and the third h arm on ic condition w a s 1 0 .8 5 . H ow ever, s ta tis tic a l a n a ly sis did not in d icate sig n ifica n t d iffe re n c e s betw een th e se m ea n s. Although the d iffe re n c e s in d icated that secon d h arm on ic d is tortion condition produced c o n siste n tly h ig h er s c o r e s than did the third h arm on ic condition, the d iffe r e n c e s w e r e not s ta tis tic a lly s i g n ifican t. The in teraction of trea tm en t con d ition s by te s ts is p r e sen ted in table 5. F te st a n a ly sis of the in ter a c tio n s p r e se n ted in tab le 5 gave a value of 2. 32 w hich, w ith 16 and 125 d e g r e e s o f freed om , w a s found T A B L E 5 MEAN PE R C E N T CORRECT FOR SE N T E N C E INTELLIGIBILITY SCORES FOR THE FIVE CONDITIONS ON THE FIVE TESTS C onditions ests 1 2 3 4 5 1 12. 67 1 1 .1 3 12. 13 9. 50 11. 50 2 13. 16 1 2 . 20 1 0 . 6 2 11. 57 9. 50 3 11. 33 12. 25 11. 33 10. 87 1 0 . 16 4 1 2 . 66 1 0 . 20 13. 00 1 1 .1 4 11. 87 5 1 0 . 66 11. 87 8 . 25 10. 25 1 0 . 12 59 to b e s t a t is t ic a lly sig n ific a n t b eyon d the . 01 le v e l of co n fid en ce. T his finding in d icated that for a g iv en con d ition , th e r e a r e sig n ific a n t d if f e r e n c e s am ong s c o r e s ob tain ed fro m the fiv e s e n te n c e in te llig ib ility t e s t s . F or p u r p o se s o f d e te r m in in g the r e la tio n s h ip b etw een a g e and p e r fo r m a n c e on o th er te s ts a d m in is te r e d , the su b jec t sa m p le w a s d iv id ed into two g ro u p s. The fir s t grou p w a s c o m p o s e d o f a ll su b jec ts l e s s than 59 y e a r s of a ge. T h is group w a s d e sig n a te d the " ad u lt” group. The s e c o n d group w a s c o m p o se d of th o se su b jec ts o v e r 59 y e a r s o f age and w a s d e sig n a te d the " g e r ia tr ic " group. T he a g e of 59 w a s the m e a n a ge o f the su b jec t s a m p le . D iffe r e n c e s b etw een th e s e groups w e r e ex a m in ed for the fo llo w in g v a r ia b le s : (1 ) s p e e c h r ec e p tio n th r e sh o ld (SRT), (2) sp e e c h d is c r im in a tio n (SDS), (3) m o s t c o m fo r ta b le lo u d n e ss le v e l (M CL). and (4) co n d itio n s 2, 3, 4, and 5. The s u m m a r y o f a n a ly s is o f th e s e data is p r e se n te d in ta b le 6 . The t^-test a n a ly s is p e r fo r m e d on the d iffe r e n c e s b etw een "adults" and " g e r a tr ic s " grou p s in d ica ted that "adults" and " g e r ia tr ic s " did not d iffe r s ig n ific a n tly on c o n d itio n s 2, 3, 4, and 5. A d d ition al t_-tests in d ica ted that the two g ro u p s did not d iffer s ig n if ic a n tly in SDS and M CL, but did d iffe r sig n ific a n tly in SRT, T he 60 TABLE 6 STATISTICAL COMPARISONS BETW EEN SCORES FOR "ADULTS" AND "GERIATRICS" ON CONDITIONS 2, 3, 4, 5, SRT, MCL, AND SDS "Adults" "G eriatrics" V ariab le (m ea n s) (m eans) D ifferen ce t - T est c L Condition 2 11. 32 11. 24 . 08 N. S. a Condition 3 1 0 . 90 1 0 . 89 . 01 N. S. Condition 4& 1 1 . 06 1 1 .1 3 . 07 N. S. E L Condition 5 1 1 . 06 1 0 . 80 . 26 N. S. SRT in dB 41. 66 50. 53 00 00 2. 07* MCL in dB 77. 00 79. 66 2 . 66 N. S. SDS P B s % c o r r e c t 75. 73 70. 40 5. 33 N. S. Significant at 0. 05 confid en ce le v el. P e r ce n t co rrect. " g eria trics" group placed sig n ifica n tly h igh er than the "adult" group on this m e a su r e. Sum m ary In su m m ary, the data co llected from the sp eech in tellig ib ility te s ts indicated sign ifican t d ifferen ces am ong the five treatm ent condi tion s. S p ecifica lly , the data indicated that the sp eech in tellig ib ility s c o r e s o f condition 1 w e r e sign ifican tly higher than the sp eech 61 in tellig ib ility s c o r e s o f the rem ain in g con d ition s. A dditionally, the data indicated that the sp e ec h in tellig ib ility s c o r e s of condition 2 d iffered sig n ifica n tly w hen com p ared w ith conditions 4 or 5. A lso , the data ind icated that the sp e ec h in tellig ib ility s c o r e s of condition 3 w e r e sig n ifica n tly h igh er than the s c o r e s for conditions 4 or 5. With r e s p e c t to seco n d and third h a rm o n ic d istortion , the data indicated d iffe re n c e s in favor o f b etter s c o r e s under the secon d h arm on ic condition, but th ese d iffe r e n c e s w e r e not sign ifican t. With r e s p e c t to the w id e and n arrow freq u en cy ran ges, th ese data in d icate that th ose individuals rec e iv in g the n arrow freq u en cy range p laced sig n ifica n tly low er than th o se individuals r ec e iv in g the w id e frequency range. With r e s p e c t to d iffe r e n c e s betw een "adults" and " g e ria trics" groups, the data indicated sp e e c h recep tion th resh o ld s w e r e sig n ifica n tly h igh er for the " g e ria trics" group. The data ind i cated no sig n ifica n t d iffe re n c e s b etw een the two groups for the d is torted conditions 2, 3, 4 and 5, MCL or SDS. C H A P T E R V DISCUSSION O F R E SU L T S A b r ie f d e s c r ip tio n o f th o se con d ition s w ith w h ic h w e a r e c o n c e r n e d m ig h t b e u s e fu l in p ro v id in g s o m e in sig h t to the r e a s o n s for settin g th o se p a r a m e te r s c h o se n for the ex a m in a tio n o f the e ffe c ts o f d isto r tio n as th ey r e la t e to th e p r o b le m s o f day to d ay u n d ersta n d in g th rou gh a low fid elity , d isto r tin g a m p lifie r . W hen one e x a m in e s the co n d itio n s o f u s e o f h e a r in g a id s , it b e c o m e s ap p aren t that a la r g e p o rtion of the u s e r ' s day is sp en t in lis te n in g in a b ack grou n d of n o is e and a id s a r e n o r m a lly a d ju sted b y the u s e r for th e m o s t c o m fo r ta b le liste n in g le v e l (M CL). In addition, e x p e r ie n c e g a in ed in e x a m in in g h e a r in g aid r e s p o n s e c h a r a c t e r is t ic s h as show n the m a jo r ity o f h e a r in g a id s exhibit v a ry in g d e g r e e s of sec o n d h a rm o n ic and th ird h a r m o n ic d isto rtio n and that fr e q u e n c y r e s p o n s e ra n g es g e n e r a lly fa ll into two d is tin c t p a ttern s: p a ttern s that a r e r e la t iv e ly w id e (200 th rou gh 4000 Hz) or r e la t iv e ly n a rro w (200 through 2500 Hz). E x p e r ie n c e w ould s e e m to in d ica te a ls o , that 62 63 in m o st c a s e s the w id er frequency range is m o re d e sira b le than n a r row er frequency ranges. Thus, in attem pting to approxim ate th ese conditions, distorted and un distorted sen ten ces p resen ted at MCL, varying in frequency r esp o n se ranges in a background of n o ise, w e r e chosen to explore the problem . The selectio n of MCL as the p resen tation le v e l for the s e n ten ces w a s an arb itrary but reason ab le d ecisio n , as MCL is u tilized routin ely in day to day evaluation of hearing. H ow ever, its u se is not w ithout p recedent, C arhart recom m en d ed MCL as a m eans of e sta b lish in g equal inten sity le v e ls for sp eech betw een hearing aids. He stated that "E stablishm ent of MCL is an accepted p roced u re co m m o n ly u sed in the selectio n of hearing aids. " Young and Gibbons rep ort the u s e of MCL as one of the stand ard p roced u res u tilized by the v etera n 's adm inistration in the m e a s - 2 u rem en t of d iscrim in ation for sp eech . M arkle and Zaner studied the effects of hearing aid gain on sp eech d iscrim in ation sc o r e s and rep orted im proved d iscrim in ation for sp eech when gain w as set to Raymond Carhart, "Volum e C ontrol A djustm ent in H earing Aid S election, " The L a ry n g o sco p e, LVI (N ovem ber, 1946), 780-794. 2 Martin Young and Edward Gibbons, "Speech D iscrim in ation and T hreshold M easu rem en ts in a N on -N orm al H earing Population, " Journal of Auditory R e se a r c h , II (January, 1962), 21-33. p ro v id e the le v e l judged to b e m o s t co m fo rta b le. In exam ining the r e la tio n b etw een le v e ls u sed for M CL and m ea n s e n te n c e in te llig ib ility s c o r e s a c r o s s the five co n d itio n s, the m ea n s c o r e for MCL of 70 d e c ib e ls w a s found to be 1 1 .1 9 p e r c e n t c o r r e c t , fo r MCL of 75 d e c ib e ls , 11. 87 p e r ce n t c o r r e c t, and for M CL o f 80 d e c ib e ls , 10. 95 p e r c e n t c o r r e c t. It is apparent that th ere is little v a r ia tio n in th ese m e a n in te llig ib ility s c o r e s a s a function o f MCL le v e l . The m eans a t M CL 90 d e c ib e ls and 95 d e c ib e ls w e r e 1 1 . 9 0 and 1 1 .8 2 p ercen t c o r r e c t , r e s p e c tiv e ly , again show ing little v a r ia tio n . At MCL of 85 d e c ib e ls , h o w ev er, the m ean p e r ce n t c o r r e c t w a s 9 .4 6 . Subject data fo r th e s e in d ivid u als r e v e a le d e x tr e m e ly low d is c r im in a tio n sc o r e s and, in addition, th ere w e r e on ly th re e in d iv id u a ls in th is category, a n u m b er in su ffic ie n t to attach sig n ific a n c e . A p ilo t study con d u cted in itia lly w ithout n o is e background during p r e se n ta tio n of p h o n e tic a lly b alan ced w o rd s (P B 's) ind icated no d if fe r e n c e s e ss e n tia lly , b etw een d isto r te d and u n d isto rted c o n d i tio n s. J e r g e r reported th e s a m e r e s u lt u sin g P B 's in h is e a r lie r 4 study. Subjects w e re a b le to c h o o s e c o r r e c t ly w ithout any ap p arent 3 D onald M arkle and A nnette Z aner, "The D eterm in a tio n o f Gain R eq u ir e m e n ts of H ea rin g A id s: A New M ethod, " The Jou rn al of A u d ito ry R e se a rc h , VI (O ctob er, 1966), 3 7 1 -3 7 7 . 4 J a m e s J erger, " B e h a v io r a l C o r r e la te s o f H earing Aid R e sp o n se , " B ulletin of P r o s th e tic R e s e a r c h , B PR 1 0 -7 (Spring, 1967), 6 2 -7 5 . d ifficu lty , in q u iet. T he s a m e r e s u lt w a s found w ith the s e n te n c e s . T hus, the e ffe c ts o f d is to r tio n upon s e n te n c e in te llig ib ility w e r e not r e a d ily d e m o n str a b le u n d er q u iet c o n d itio n s. T h irty p e r c e n t d is t o r tion w a s thought to be su ffic ie n t to d e m o n s tr a te d if fe r e n c e s b etw een se c o n d h a r m o n ic and th ird h a r m o n ic d isto r tio n . That th is did not p r o v e to b e the c a s e in q u iet, s u g g e s ts the im p o r ta n c e o f d isto r tio n is in its in ter a c tio n w ith n o is e in th e en v ir o n m e n t. N o is e a lo n e w ill, o f c o u r s e , r e d u c e in te llig ib ility . N o is e p lu s d isto r tio n w ill r ed u c e in t e l lig ib ility a ls o . S in ce d isto r tio n is a c h a r a c t e r is t ic o f h ea rin g aid a m p lif ie r s , it w ou ld s e e m to follow that c o n sid e r a tio n o f the in t e r a c tion of n o is e and d isto r tio n in h e a r in g a id s is im p ortan t. B u rn ett fe e ls that the im p o r ta n c e of d isto r tio n in h e a r in g a id s is that it can c a u s e a s ig n ific a n t n u m b e r of fa ls e c lu e s in c e r ta in f r e - 5 q u en cy a r e a s as w e ll a s m a s k th e fu n d am en tal r e s p o n se . The s p e e c h sp e c tr o g r a p h s in fig u re 6 show the e ffe c ts o f d is to rtio n a s d istu r b a n c e o f the r e g u la r and w e ll fo rm ed h a r m o n ic p a t te r n s p r e s e n t w ith o u t d is to r tio n . D isto r tio n o f the r e g u la r ity of h a r m o n ic s tr u c tu r e in s p e e c h m a y b e p a r tly r e s p o n s ib le for d e t e r i o ra tio n o f in te llig ib ility . E dw in B u rn ett, "A N ew M ethod for the M e a su r e m e n t o f N o n lin e a r D isto r tio n , n B u lle tin o f P r o s th e tic R e s e a r c h , B P R 1 0 -7 (Spring, 1967), 7 6 -9 1 . 66 The finding of sign ifican t d iffe r e n c e s b etw een the d isto r te d conditions and th e u n d istorted condition for sen ten ce in tellig ib ility w ould s e e m to be c o n siste n t w ith w hat one m igh t expect if the q u estion w a s asked: w ill d isto rtio n d e c r e a s e in tellig ib ility ? C om m on s e n s e w ould s e e m to d icta te an a ffirm a tiv e an sw er to the question . H ow ev er, it is am p ly d em on strated in the lite r a tu r e that d isto rtio n s of g r e a t m agnitude and variation a re r e s is te d by the ear and p e r fo r m ance is not g r e a tly affected by m o s t typ es o f d istortion including secon d and third h a r m o n ics. T h ere a re s e v e r a l fa cto rs to be c o n sid e r e d in explanation of th ese d iffe r e n c e s. M ost of the in v e s tig a tions of d isto rtio n and its effects on in tellig ib ility w e r e co m p leted on n o rm a l e a r s . This study u se d n o n -n o rm a l e a r s . O lsen and C arhart in v estig a ted the effe cts o f d isto rtio n u sin g im p aired e a r s and c o n cluded that for the conditions in th eir study h arm on ic d istortion did 6 not h a v e any r e lia b le or sy ste m a tic effects on d isc rim in a tio n . It w as th eir opinion rather that the w idth o f the freq u en cy r e sp o n se range of the h ea rin g aid s u se d in th eir study w a s m o r e im portant to good in te llig ib ility than r e la tiv e ly m in o r am ounts of h arm on ic d is to r tion. This is true un der the conditions of d isto rtio n u sed in th eir study, It cannot be said, h o w ev er, that d isto rtio n did not have an 6 W ayne O lsen and Raym ond C arhart, "D evelopm ent of T est P r o c e d u r e s for B inau ral H earing A id s, " B ulletin of P r o sth e tic R e s e a r c h . BPR 10-7 (Spring, 1967), 2 2 -4 9 . 67 effect. D isto r tio n did h a v e an e ffe c t on d is c r im in a tio n in th e ir study. It w a s not a c o n s is t e n t or r e lia b le e ffe ct h o w e v e r. A d d ition ally, the lit e r a t u r e on in form ation th eo r y w ou ld s u g g e s t the p ro b a b ility o f g r e a t e r e a s e of in te llig ib ility for s e n te n c e s v e r s u s s in g le w o r d s . T his b e c a u s e a sen te n c e c a r r i e s m o r e in fo r m a tion to th e lis t e n e r than d o e s a s in g le w ord. A s e n te n c e is a red u n d ant m e s s a g e and r e p r e s e n ts a r e s t r ic t e d se t o f p o s s ib le a n s w e r s , w h e r e a s , a lis t e n e r r eq u ir ed to r e c e iv e a sin g le w o r d has an a lm o s t in fin ite s e t of p o s s ib le a n s w e r s fro m w h ich to c h o o s e . A lthough s in g le w o r d s a r e c o m m o n ly u s e d in d isc r im in a tio n t e s t s , J e r g e r has 7 found th em to be in d ep en d en t o f c h a r a c t e r is t ic s o f h e a r in g a id s. Our p u rp o se h e r e , h o w e v e r, w a s co n cern ed not w ith in te llig ib ility o f s in g le w o r d s but w ith in t e llig ib ility o f u n d isto r te d s e n te n c e s v e r s u s d is to r te d s e n te n c e s . F o r co n d itio n s u s e d d u rin g this study th e r e w a s a c o n s is t e n t d iffe r e n c e in favor o f b e tte r in te llig ib ility w ith u n d isto r te d s e n te n c e s . Thus it s e e m s r e a s o n a b le to g iv e an a ffir m a tiv e a n s w e r to the q u e s tion: w ill d isto r tio n d e c r e a s e in te llig ib ility ? T h is w ou ld s e e m e s p e c ia lly tru e for h e a r in g im p a ir e d in d ividu als, w e a r in g low fid elity in str u m e n ts in a b ackgroun d o f n o is e . 7 J a m e s J e r g e r , " B e h a v io r a l C o r r e la te s o f H ea rin g A id P e r fo r m a n c e , " B u lletin o f P r o s t h e t ic R e se a r c h , B P R 10-1 (Spring, 1969), 6 2 -7 5 68 As to the effects of secon d v e r s u s third harm on ic distortion , the data in this study tends to lend support to the idea that third h a r m onic distortion is m o r e d etrim en tal than secon d harm onic distortion 8 9 and in agreem en t, th erefo re, w ith L ick lid er and W atson and Tolan 10 and in d isa g reem en t w ith D avis and S ilverm an . Although the data indicate no sign ifican t d ifferen ces betw een secon d and third h arm on ic d istortion , it did indicate so m e d ifferen ce. The d ifferen ce obtained indicated b etter s c o r e s under the second h a r m onic condition. It has been the p ra c tic e o f the San D iego Speech and H earing C enter to m e a su r e the am ount of second harm onic distortion routin ely for all h earin g aids evaluated. T ill now, third harm onic distortion has not been m e a su r ed routinely. This is a lso the p ra ctice of other fa c ilities w ith w hich the w r ite r is acquainted. In view of this finding, it would see m prudent to m e a su r e third harm on ic distortion a s a m atter of routine in the evaluation o f hearing aids and is now the p ra c tic e of the San Diego Speech and H earing C enter. g J. C. R. L ick lid er, "E ffects of A m plitude D istortion upon the In telligib ility of Speech, " The Journal of the A cou stical S o ciety of A m e r ic a , XVIH (October, 1946), 4 2 9 -4 3 4 . 9 Leland A. W atson and Thom as Tolan, H earing T ests and H earing Instrum ents (B altim ore: The W illiam s and W ilkins Company, 1949), 333. ^ H a llo w e ll D avis and R ichard S. S ilverm an , Hearing and D eafn ess (B altim ore: The W illia m s and W ilkins Company, 1949), 316. 69 The a b se n c e of any sig n ifica n t d iffe r e n c e s betw een secon d h arm on ic and third h arm on ic d isto rtio n m a y su g g e st that th ere is no sig n ifica n t effect or that the effect, if it d oes ex ist, did not e x is t for the su b jects or conditions u sed in this study. W ith r e s p e c t to w id e and narrow freq u en cy ran ges, the data in th is study is supported by data of O lsen and C arhart w ho found w id er frequency r e sp o n se range p rodu ces h igh er d iscrim in a tio n s c o r e s . T his study has produced inform ation con cern in g the effe cts of d istortion and freq u en cy r e sp o n se range on sen ten ce in tellig ib ility through a low fid elity s y ste m . M ost of the r e s e a r c h p reced in g this study u sed the stand ard m ethod for m e a su r in g d isto rtio n , i. e. , d is tortion at th ree d is c r e te freq u en cies only. This w as the fir s t study to m e a s u r e d istortion through the entire frequency range of the a m p li fier. The findings su g g e st that n o n -lin e a r d istortion , n a m ely secon d and third h a rm o n ic d istortion , m ay have a d ifferen tia l effect on in te l lig ib ility and that the effects of third h arm on ic d isto rtio n m a y be m o r e d etrim en ta l to sp e e c h in tellig ib ility than secon d h a rm o n ic d is tortion. The findings a r e im portant a s they co n firm the im p ortan ce of having r e la tiv e ly w id e freq u en cy r e sp o n se in h earin g aids as opposed to the r e la tiv e ly n a rro w freq u en cy r e sp o n se co m m o n ly found in m any c o m m e r c ia lly a v a ila b le h earin g aids on the m a rk et today. C H A P T E R VI SUM M ARY A N D CONCLUSIONS S u m m a r y T he p u rp o se o f th is stu d y w a s to in v e s tig a te the e ffe c ts of d is to rtio n on s e n te n c e in te llig ib ility . The s p e c if ic o b j e c tiv e s o f the stud y w e r e to d isc o v e r : (1) w h e th e r seco n d h a rm o n ic d is to r tio n or th ird h a rm o n ic d isto r tio n had th e g r e a t e r d e le te r io u s e f f e c t on s e n te n c e in te llig ib ility and w h e th e r the e ffe c t o f th e s e d is to r tio n s w as s ig n ific a n tly d iffe re n t w hen c o m p a r e d to s e n te n c e in t e llig ib ility under u n d isto rted co n d itio n s, (2) the e ffe c ts upon s e n te n c e in t e llig ib ility in a m a n n er a p p ro x im a tin g the co n d itio n s of h e a r in g aid u s a g e in n orm al d ay to day e x p e r ie n c e , (3) the e ffe c ts o f d isto r tio n a s th e y m igh t a c c r u e to u s e r s of h e a r in g a id s w ith n a rro w fr eq u en cy r e s p o n s e r a n g e s and to u s e r s o f h e a r in g a id s w ith w id e r fr e q u e n c y r e sp o n se r a n g e s, and (4) the e ffe c ts o f h a r m o n ic d isto r tio n for in d iv id u a ls with s e n s o r i- n e u r a l l o s s e s . The s p e c ific h y p o th e se s te s te d in th is study w e r e : (1) th ere 70 71 w ill be significan t differences betw een sen ten ce in tellig ib ility s c o r e s using second harm on ic d istortion and third h arm on ic distortion , (2) there w ill be sign ifican t d ifferen ces betw een sen ten ce in tellig ib ility s c o r e s using un distorted and d istorted conditions, (3) th ere w ill be sign ifican t d ifferen ces betw een sen ten ce in tellig ib ility s c o r e s using w ide band freq u en cy resp o n se and narrow band frequency resp o n se. The litera tu re pertinent to the problem indicated co n sid era b le d iv e r se n e ss of opinion as to w hat kinds of d istortion , if any, a re detrim en tal. Much of the av a ila b le litera tu re is con cern ed w ith d is tortion as it is related to p r im a r ily c o m m e r c ia l applications o f high fid elity a m p lifiers and to tw o-w ay com m unication s y ste m s such as telephones and radio. The liter a tu r e r ev e a ls the rem ark ab le ability of the n orm al human auditory s y ste m to r e s is t the effects of d is to r tion. D esp ite the fact that the sy ste m is r ela tiv ely r esista n t to d is tortion, co n sid era b le tim e and effort has been expended in the d evelop m ent of effectiv e com m u nication sy ste m s w ith m in im al distortion c h a r a c te r is tic s. M ost of the rep orted in vestigation s have been d i rected toward sy ste m s u tilized by n o rm a lly hearing individuals. Thus, it w ould appear that d esp ite the auditory ab ility to r e s is t d is tortion, distortion in com m u n ication s s y ste m s is a problem of so m e m agnitude. It s e e m s apparent th erefore that distortion in the e le c t r o acou stic d e v ic es w orn by the hearing im p aired should be of so m e 72 im p o rta n ce. Only w ithin the la s t d eca d e h a v e c o n c er te d efforts been m ad e to study the effects o f d isto rtio n on in te llig ib ility a s it a ffe c ts the h ea rin g im p a ired . The su b jects u tiliz e d in th is study w e r e th irty adult p atien ts w ith s e n s o r i-n e u r a l h ea rin g lo s s taken from the d a ily c a se lo a d of the San D iego S p eech and H earin g C en ter. T hey w e r e req u ired to lis te n to five sen te n c e in te llig ib ility te s t tap es u n d er five d ifferen t con d ition s u sin g a fo rced c h o ic e techniq ue. E ach tape c o n s iste d of 15 m u ltip le c h o ic e se n te n c e s and su b jec ts w e r e req u ired to u n d erlin e th eir a n sw er on the a n sw e r s h e e t s . Data w e r e c o lla te d and su b jected to tw o -w a y a n a ly sis o f v a r i a n c e and a te s t of s ta tis tic a l c o m p a r is o n s , a m o d ified t_ te s t. W ith r e s p e c t to h y p o th esis n u m b er 1, w h ich w a s c o n c e r n e d w ith d iffe r e n c e s in s e n te n c e in te llig ib ility s c o r e s u n d er con d ition s o f seco n d and third h a r m o n ic d isto rtio n , the data in d icated no sig n ific a n t d iffe r e n c e s. The m ean s c o r e for the sec o n d h a rm o n ic d isto r tio n condition w a s 11. 00 and for the third h a rm o n ic d isto rtio n con d ition w as 10. 85. T h e r e fo r e , b a sed upon a n a ly sis o f th e s e data, h y p o th esis 1 w as r e je c ted . 73 W ith r e s p e c t to h y p o th e s is II, w h ic h w a s c o n c e r n e d w ith d if f e r e n c e s in s e n te n c e in t e llig ib ilit y b e tw e e n the u n d is to r te d c o n d itio n and th e d is to r te d c o n d itio n s , the data in d ic a te d th at the s p e e c h in t e l lig ib ility s c o r e s ob ta in ed u n d er c o n d itio n 1, the u n d isto r te d co n d itio n , w e r e s ig n ific a n tly d iffe r e n t fr o m in t e llig ib ility o b tain ed u n d er the d is to r te d c o n d itio n s . H y p o th e sis II w a s not r e j e c t e d . W ith r e s p e c t to h y p o th e s is III w h ic h w a s c o n c e r n e d w ith d if f e r e n c e s in s e n te n c e in t e llig ib ilit y b e tw e e n n a r r o w and w id e fr e q u e n c y r e s p o n s e r a n g e , th e data in d ic a te d th a t th e s p e e c h in t e llig ib ility s c o r e s w e r e h ig h e r w h e n s u b j e c ts lis t e n e d to th e w id e r fr e q u e n c y r a n g e . T he m e a n s c o r e s fo r the w id e ra n g e w e r e 11,20 and fo r th e n a r r o w ra n g e 10.65. T he d if f e r e n c e s b e tw e e n th e s e m e a n s w e r e found to b e s t a t is t ic a lly s ig n ific a n t. T h e r e f o r e , h y p o th e s is M w a s not r e j e c t e d . T h e data fr o m th e stu d y in d ic a te d th e fo llo w in g d if f e r e n c e s : (1) s p e e c h in t e llig ib ilit y s c o r e s fr o m c o n d itio n 1, th e u n d is to r te d c o n d itio n , w e r e s ig n ific a n tly h ig h e r than the s p e e c h in t e llig ib ility s c o r e s of th e r e m a in in g c o n d itio n s , (2) s p e e c h in t e llig ib ilit y s c o r e s un d er the s e c o n d h a r m o n ic co n d itio n w e r e n ot s ig n ific a n tly h ig h er th a n s p e e c h in t e llig ib ilit y s c o r e s u n d er the th ird h a r m o n ic c o n d itio n , and (3) s p e e c h in t e llig ib ilit y s c o r e s of s u b je c ts w e r e s ig n ific a n tly h ig h e r u n d er the w id e fr e q u e n c y r e s p o n s e ra n g e than u n d er the 74 n a r r o w er freq u en cy r e s p o n s e ran ge. A m ong the four co n d itio n s of s e n te n c e s w ith d isto rtio n , condition 2 d iffered s ig n ific a n tly when co m p a red w ith con d ition s 4 or 5 and condition 3 a ls o d iffe re d s ig n ifi ca n tly w hen co m p a r e d to con d ition s 4 or 5. C o n clu sio n s W ithin the lim its o f this e x p erim en t, the follo w in g c o n c lu sio n s ap p ear w arran ted : 1. H arm on ic d isto rtio n red u ced s e n te n c e in tellig ib ility . 2. S en ten ce in te llig ib ility s c o r e s w e r e h ig h er under seco n d h a rm o n ic d isto rtio n co n d itio n s than under th ird h a rm o n ic con d ition s, but not sig n ifica n tly so. 3. S en ten ce in te llig ib ility s c o r e s w e r e h ig h er u n d er w id e freq u en cy r e sp o n se ran ge co n d itio n s than u n d er n a r r o w e r freq u en cy r e s p o n se ran ge co n d itio n s. The findings o f this study s u g g e s t the im p o rta n c e o f c o n s id e r ing the effe cts of n o n -lin e a r d isto r tio n on s e n te n c e in te llig ib ility of h ea rin g im p a ired in d ivid u als and that the less d isto r tio n p r e se n t in the a m p lifie r s u tiliz e d by the h ea rin g im p a ired , the g r e a te r th eir opportunity for b e tter in te llig ib ility . A P P E N D I C ES 75 A P P E N D IX A AUDITORY TEST SE N T EN C E S TA PE D FROM P A L # 8 (as m od ified by J e r g e r , H ouston Sp eech and H earing C enter) 76 ORDER OF M U L T IPL E CHOICE T EST SE N T EN C E S AUDITORY T E S T #1 1. T he n u m ber of fin g e r s on an a v e ra g e hand is: 2. What is th e nu m b er b efo re s ix ty -n in e ? 3. How m an y " lls ,, a r e th e r e in the a lp h ab et? 4 . B ow s are u s e d to shoot: 5 . U n d erlin e the w o rd that con tain s the le tte r "T". 6 . W hat is the su m of tw o p lu s fiv e ? 7 . U n d erlin e th e w o rd chunk. 8 . S om eth in g that w e ig h s a g r e a t d ea l is: 9- U n d erlin e la d d er . 10. What is s ix t im e s tw o ? 11. The c o ld e st land is: 12. W hich is s m a lle r , s i x or tw o ? 13. What is s e v e n and fiv e ? 14. T he thing w h ich is s a lty is: 15. The co ld w ea th er en d s in: 78 A U D IT O R Y T E S T #2 1. B e tw e e n th e h ea d and le g is the: 2 . A m i l e - r a c e h as: 3. W hich m e a l is n e a r e r m id n ig h t? 4 . The lo n g e s t w o r d of t h e s e fo u r is : 5. We m e a s u r e h ea t w ith a: 6 . The m a n w h o fig h ts w ith g lo v e s is a: 7. Is eig h t m o r e th a n th r e e p lu s th r e e ? 8 . W hat m o n th c o m e s a fte r S e p te m b e r ? 9. L ondon i s th e n a m e of a c ity in: 10. W hat is th e n u m b er to th e r ig h t of t h ir t y -e ig h t ? 11. H a lf of te n is: 12. W hen it g e t s v e r y c o ld , w a te r b e c o m e s : 13. T o b a c c o is s m o k e d in: 14. Y ou can g e t drunk fr o m : 15. A w o lf is lik e a w ild: 79 AUDITORY T EST #3 1. A tr a in is u se d for: 2. Is m ilk the co lo r of snow ? 3. A r a ck et is u se d for playing: 4. W hat m a k es your fe e t slip ? 5. W hat in s e c t d oes honey co m e fr o m ? 6 . A m an who cannot s e e is: 7. The ta ste of a ripe apple is: 8 . T he t ir e s on a car are m ad e of: 9 . You c a tc h fis h with: 10. C oal is burned in: 11. On a c le a r day the w eath er is: 12. W hich of th ese n u m b ers is n e a r e s t fo u rteen ? 13. U n d erlin e the s m a lle s t sum of m on ey. 14. The w in n er of a r a ce is: 15. On w hat m a teria l is a n ew sp ap er p rin ted ? 80 AUDITORY T E S T #4 1. H ow m u ch is s e v e n p lu s fou r ? 2 . W h ite is the c o lo r of: 3. W h ich is the m id d le of the w e e k ? 4 . U n d e r lin e the w ord n e x t to fou r, 5. W hat num ber c o m e s a fte r e ig h ty ? 6 . F lo u r is u sed to m a k e: 7 . W hat le tte r c o m e s a fte r "B"? 8 . W hat is the n u m ber to th e le ft of fiv e ? 9. W h en d o e s the m o o n s h in e ? 10. H ow m an y le g s d o e s a duck have ? 11. W h ich g o e s w ith th e g r e a t e s t sp e e d ? 12. W h e r e is P a r is lo c a te d ? 13. T h e thing w ithout any le g s is: 14. U n d er lin e the la s t one of th e s e w o r d s . 15. H ow m u ch is nine m in u s th r e e ? 81 AUDITORY TEST #5 1. The thing w hich cannot fly is: 2. A g ir l with ligh t c o lo red h air is: 3. A good fight n eed s good: 4 . The one w h ich ea ts g ra in is: 5 . A p e r so n w ith m u ch m on ey is: 6 . The c o lo r of c h e r r ie s on t r e e s is: 7 . A w h e e l is found on a: 8 . P e a r ls are found in: 9. W hen we add fiv e to tw e lv e , w e g e t? 10. W hich of th e s e is the le a s t loud? 11. N am e the sound m a d e by a cat. 12. B efo re it b e c o m e s a fr o g , it is c a lle d a: 13. Is a h ill la r g e r than a m ou ntain ? 14. B ooks are p rin ted on a: 15. U nderline the w o rd "Bun". A P P E N D IX B ANSW ER SH EETS FOR INTELLIG IBILITY TESTS 82 83 1. 2 . 3. 4 . 5. 6 . 7. 8 . 9- 1 0 . 1 1 . 1 2 . 13. 14. 15. A N SW ER S H E E T A U D IT O R Y T E S T #1 10 N a ils 69 58 70 68 T w en ty - s ix One L M Indian s A r r o w s R a p id s Guns T e a r C ig a r V a m p Do 11 10 Junk C hum p S h ru n k Chunk H ea v y D og E x p e n s iv e C a r d -p la y e r L itte r L ad d er L e t t e r L atter 12 A la s k a Ice E s k im o M ines 8 1 35 12 O cean R otten F o o d B ro k en -d o w n F u r n a c e s F r e e z in g T ick lin g S p rin g 84 ANSW ER SH E E T AUDITORY T EST #2 1. L eg B od y H ead F o o t 2. K in d n ess Slow R un ners F ood 3. 10A.M. Lunch Supper 1 1 P . M . 4. 7 4 C ar U m b r e lla 5. Hot S u m m e r T h e r m o m e te r Stove 6 . S o ld ier B u lly C old B o x er 7. 6 Y e s N o 11 8 . A u gu st O ctober N o v em b er Autum n 9. Sunday E nglan d W ash in gton Rom e 10. 30 38 25 72 11. 1 0 -1 /2 5 20 10 12. N orth P o le W inter Ice M in es 13. P ip e s F ir e W indow L e a v e s 14. Donuts Soup A lc o h o l W asp 15. D en S h eep D og B ark 85 A N SW ER SH E E T A UDITO RY T E S T #3 1. L iftin g B u rn in g T r a v e lin g F ly in g 2 . N o W hite Y es W inter 3. M u sic T en n is Shooting Loud N o is e 4 . K ey h o le M a ttr e ss M at F lo o r w a x 5. H iv e B e e C r ic k e t T r e a s u r y 6 . B lin d G la s s e s D ark In v isib le 7. Round R ed S w e e t C id er 8 . Round S te e l Rubber G la ss 9. F o r k s L a s s o e s H ooks F o o d 10. Ground S to v es C e lla r s N o rth P o le 11. G ray Sunny B lue P ic n ic 12. 13 17 B aby 2 W eek s 13. D w a rf F lo w e r 5 C ents M ou se 14. R e fe r e e F i r s t H u rd ler L a st 15. N e w s P r e s s P a p e r R ep o rter 86 ANSWER SHEET AUDITORY TEST #4 1. 11 28 3 4 2. C olor B lack D ark Snow 3. 15 Strong W ed n esd ay Sunday 4 . Q uarter D im e H alf Four 5. 40 81 1 /2 80 6 . B read W heat G arden V a se 7 . E H W C 8 . 11 9 5 Hive 9 . D ay N ight Sun Sky 10. 2 4 1 W ebs 11. H orse A irplane B oat L o co m o tiv e 12. New York C o m p a ss F ra n ce E ngland 13. C entipede F is h M an D og 14. Ten Judgm ent One Old 15. 6 27 15 12 87 ANSW ER SH EET AUDITO RY T E ST #5 1. E a g le A irp la n e S k y sc r a p e r S p arrow 2. B row n B ru n ette B londe R edhead 3. B o x e r s L a n tern E y e s P ilo t 4 . T ig e r H o r se B a rn C an cer 5. R ich F a t Bank B ee 6 . T r e e s S w eet B row n Red 7. W agon C ir c le F ish in g Rod S h o es 8 . O y s te r s D o r m ito r ie s H air B ook s 9 . Lunch 17 21 7 10. C r im e S h ort H o a r se W h isp er 11. Squeak R oar B ark P u rr 12. Sw indle M ist T adpole Puppy 13. Y es Mt. E v e r e s t D rinkin g W ater No 14. C o m p a ss P r in tin g P r e s s A uthor F e e t 15. Gum Gun Bun B um A P P E N D IX C G R A Y 'S O R A L READING T E S T 88 89 GRAY'S ORAL READING TEST One o f the m o st in ter e stin g birds w h ich ever liv ed in m y b ird ro o m w a s a blue jay n am ed Jackie. He w a s full of b u sin e ss from m ornin g till night, s c a r e c e ly ev er s till. He had been stolen from a n e st long b efore he could fly, and he has been rea red in a h o u se long b efo re he had been given to m e as a pet. A P P E N D IX D AUDIO M ETRIC A N D M ED IC A L D A T A FOR SU B JE C T S 90 91 A u d iom etric and M ed ical D ata for Subjects Subject Sex Age Ear SDS % SRT dB M C L dB Diagnosis 1 M 51 R 80 25 70 S e n so r i- neural 2 M 39 R 80 50 80 Sens ori- neural 3 M 70 L 72 55 95 Sens ori- neu ral 4 M 18 R 56 26 70 S e n so r i- neural 5 F 58 R 80 6 0 90 Sens o ri- neural 6 F 70 R 6 0 44 75 S e n so r i- neural 7 M 64 L. 8 8 55 75 Sens ori- neural 8 M 76 L 6 0 60 80 Sens ori- neural 9 F 83 L 8 6 40 70 S e n so r i-n e u r a l 1 0 M 77 R 64 50 75 S e n so r i-n e u r a l 11 M 83 L 72 30 70 S ens ori- neural 12 F 56 R 80 35 75 Sens ori- neural 13 F 45 R 6 0 40 80 Sens ori- neural 14 F 75 R 6 0 60 90 Sens o ri- neural 15 F 78 R 58 60 85 S ens ori- neural 16 M 63 L. 76 50 80 S e n so r i-n e u r a l 17 F 58 L, 94 34 75 Sens ori- neural 18 F 65 R 62 52 80 Sens ori- neural 19 M 45 R 6 8 64 85 S e n so r i-n e u r a l 2 0 M 79 R 56 64 95 S e n so r i-n e u r a l 2 1 M 63 R 80 28 70 Sens o ri- neural 2 2 F 54 Li 8 8 36 70 Sens ori- neural 23 F 49 R 6 8 50 80 Sens ori- neural 24 F 62 R 72 60 75 Sens o r i-n eu ra l 25 M 51 L 70 48 80 Sens ori- neural 92 A u d io m e tr ic and M ed ica l D a ta for S u b je c ts (C ontinued) Su b ject S ex A ge E a r SDS % SRT dB M C E dB D ia g n o s is 26 F 34 L 70 38 75 S ens o r i- n eu r a l 27 F 74 lu 8 6 64 85 S ens o r i- n e u r a l 28 F 46 R 92 32 70 S en s o r i- n e u r a l 29 F 82 R 64 30 70 S en s o r i- n e u r a l 30 M 56 R 90 40 80 S en s o r i- n eu r a l A PPEN D IX E R A W SCORES ON SEN TEN C E INTELLIGIBILITY TESTS 93 ■ b ji 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Raw S co res on Sentence Intelligibility T ests Condition 1 Condition 2 T e st S c o r e* T est Score 1 15 2 14 2 15 3 15 3 11 4 11 4 8 5 7 5 15 1 15 1 11 2 13 2 13 3 8 3 13 4 15 4 15 5 7 5 8 1 9 1 10 2 8 2 15 3 12 3 8 4 6 4 14 5 9 5 8 1 11 1 15 2 15 Condition 3 Condition 4 T est Score T est Score 3 11 4 13 4 13 5 15 5 9 1 12 1 7 2 9 2 14 3 12 3 13 4 15 4 9 5 11 5 12 1 13 1 13 2 12 2 11 3 7 3 6 4 8 4 15 5 14 5 6 1 7 1 8 2 9 2 7 3 7 3 15 4 15 Raw S co res on Sentence Intelligibility T ests (Continued) Subject Condition 1 T est Score Condition 2 T est Score Condition 3 T e st Score Condition 4 T est Score Condition 5 T est Score 17 2 11 3 12 4 13 5 7 1 9 18 3 13 4 15 5 12 1 12 2 14 19 4 12 5 9 1 1 0 2 9 3 9 2 0 5 11 1 15 2 14 3 14 4 14 21 1 10 2 1 0 3 1 0 4 9 5 11 2 2 2 14 3 9 4 9 5 8 1 11 23 3 9 4 9 5 6 1 9 2 5 24 4 13 5 12 1 13 2 15 3 12 25 5 9 1 7 2 6 3 8 4 7 26 1 15 2 14 3 15 4 14 5 13 27 2 11 3 8 4 9 5 11 1 12 28 3 14 4 14 5 14 1 15 2 13 29 4 14 5 13 1 12 2 12 3 11 30 5 13 1 14 2 12 3 12 4 15 « ju Num ber c o rr e ct. vO cn B I B L I O G R A P H Y 96 BIBLIO G RAPH Y B ooks D a v is , H a llo w e ll and S ilv er m a n , R ich a rd S. 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C a rh a rt, R aym ond , " T e s ts fo r S e le c t io n o f H ea rin g A id s, " T he L a r y n g o s c o p e , L V I (N o v e m b e r , 1946), 7 8 0 -7 9 4 . Cluff, G ordon L. and P o lla c k , M ich a el C. , "T he E ffe c t o f S p e e c h H ea rin g L e v e l on S p eech D is c r im in a tio n in S e n s o r i- n e u r a l H y p a c u s ic s, " T he J o u rn a l o f A u d ito r y R e s e a r c h , IX (Jan uary, 1959), 3 2 -3 4 . F le tc h e r , H a r v e y and S tein b e rg , J. C. , " A rticu la tio n T e stin g M eth o d s, " B e ll S y s te m T e c h n ic a l J o u r n a l, VIII (O ctob er, 1929), 8 0 6 -8 5 4 . F r e n c h , N. R. and S te in b e r g , J. C , , " F a c to r s G overn in g the I n te lli g ib ility o f S p e e c h Sou nds, " T he J o u rn a l o f the A c o u s t ic a l S o c ie ty o f A m e r i c a , XIX (Jan u ary, 1947), 9 0 -1 1 9 . H a r r is , J. D. et a l. , "The R e la tio n B e tw e e n S p eech I n te llig ib ility and the E le c t r o - a c o u s t ic C h a r a c t e r is t ic s o f Low F id e lity C ir c u itr y , " The J o u rn a l o f A u d ito r y R e s e a r c h , 1(1960-1961), 3 5 7 -3 8 0 . H a r r is , J. D. , H a in e s, H. L. and M y e r s , C. K. , "T he Im p o r ta n c e o f H ea rin g a t 3 KC fo r U n d er sta n d in g S p eed ed S p eech , " The L a r y n g o sc o p e , L X X (Jan u ary, I960), 131-146. H irsh , Ira J. , S h o re, I. and C h aran , K. , " S p eech P e r c e p t io n th rou gh D iffe r e n t H e a rin g A id s, " p a p er r e a d b e fo r e A u gu st m e e tin g o f T he A c o u s t ic a l S o c ie ty o f A m e r ic a , C le v ela n d , Ohio, O cto b er, 1959. H u izin g, Henk C. and R e y n tje s, J. A. , " R e cr u itm e n t and S p e e c h D is c r im in a tio n L o s s , " T h e L a r y n g o sc o p e , LXII (M ay, 1952), 5 2 1 -5 2 6 . 99 J e r g e r , J a m e s , "B ehavioral C o r re la te s of H ea rin g A id P erfo rm a n ce," B u lle tin of P r o s th e tic R e s e a r c h , B PR 10-7 (S p rin g, 1967), 6 2 - 75. J e r g e r , J a m e s and T helin, J a m e s , "E ffects of E le c tr o -a c o u s tic C h a r a c t e r is t ic s of H earing A id s on Sp eech U n d erstan d in g, 1 1 B u lletin of P r o s th e tic R e s e a r c h , B P R 10-10 (F a ll, 1 968), 159-197. J e r g e r , J a m e s , Speaks C h a rles and M alm qu ist, C arolyn , "Hearing Aid P e r fo r m a n c e and H earing A id S electio n , " Jou rn al of Sp eech and H earin g D is o r d e r s , IX (M arch, 1966), 1 3 5 -1 4 9 . 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M ., " In telligib ility of P ea k Clipped S p eech at H igh N o ise L e v e ls , " T he Journal o f the A cou stical S o c ie ty of A m e r ic a , XXXI (January, 1959), 1 4 -1 6 . 100 P u n ch , J e r r y L. and M cC o n n ell, F r e e m a n , "The S p eech D i s c r i m i n a tio n F u n c tio n of E ld e r ly A d u lts, " T he J o u rn a l of A u d ito ry R e s e a r c h , IX ^ 'ary, 1969), 1 5 9 -1 6 5 . S h epard, F . H. , "A N ew A m p lifie r H aving C h a r a c te r is tic s S im ila r to T h o s e o f the H u m an E ar and Its A p p lic a tio n to the P r o b le m of D e a fn e s s , 1 1 T he L a r y n g o s c o p e , L (A u gu st, 1940), 7 6 7 -7 7 2 . S p eak s, C h a r le s, J e r g e r , J a m e s and J e r g e r , Susan, 'P e r f o r m a n c e C h a r a c te r is tic s of Synthetic S e n te n c e s , " J o u rn a l of S p e e c h and H ea rin g R e s e a r c h , IX (June, 1966), 3 0 5 -3 1 2 . 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Creator Hartman, Paul Wesley (author)

Core Title The Effects Of Harmonic Distortion On Sentence Intelligibility Of Hypacusic Adults

Degree Doctor of Philosophy

Degree Program Communicative Disorders

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

Tag health sciences, speech pathology,OAI-PMH Harvest

Language English

Contributor Digitized by ProQuest (provenance)

Advisor Garwood, Victor P. (committee chair), Arthur, Robert H. (committee member), Boyd, Harold M.E. (committee member)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c18-519295

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