University of Southern California Dissertations and Theses

The Effect Of Irrelevant Environmental Stimulation On Vigilance Performance

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The Effect Of Irrelevant Environmental Stimulation On Vigilance Performance

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Content T h i s d is s e rt;)tio ti h a s been M ie 0 1 -1 7 0 4 m i c r o f i l m e d e x a c t l y a s r e c e i v e d McCi RATH, .James .Joseph. Till: I I I i ( 'I IliKKI.IA A h T bN V I !i( >NM KNTA I . STIA 1 I 1 ,ATH )N ON \ I< . I ! AM T 1 M : |{ I'( MOM AM ' I n i v e r s i t y of S o u th e r n California I'h.U ., 1 !K > 1 I \s y e hoh t g y , e xpe r i n ienta I o r University Microfilms, Inc., Ann Arbor, Michigan THE EFFECT OF IRRELEVANT ENVIRONMENTAL STIMULATION ON VIGILANCE PERFORMANCE b y Jam ea J o s e p h M cG rath A D i s s e r t a t i o n P r e s e n t e d to t h e FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA I n P a r t i a l F u l f i l l m e n t o f t h e R e q u ir e m e n ts f o r t h e D egree DOCTOR OF PHILOSOPHY ( P s y c h o l o g y ) Ju n e 1961 UNIVERSITY OF S O U T H E R N CALIFORNIA GRADUATE school U N I V E R S IT Y PA RK LOS ANGELES 7 CALIFORNIA / ’/in liissi'rtiitihn, -u ritti’n Ay J a .r’F a J o s e p h V o , . ' r a t h utuirr the i/iiY iliu i o/ h .La I)iswrt/itir,n (F>tn tmHi’i', > n u l < i p pr'jVt < 1 by all its rur rnbrrs, ii,is 1 ■ ■ , /'»i >,->it,-,I /'■ ,•«,/ ... « <•/'/.-./ by t h r / )< ,m > .t !'i< (> >,i,/u-it i .St h 11. '-,n li-tl ! nltill me r.t > t y /(11 i ///(■;/11 t r: > t h i1 /■ < v , < d o c t o r o r r i m . o s o n i Y / ' ( - .1 M thitr t ; . / DISSl R I A I K )N ( . < >M M [ I I 1 I S I < (. h i2 i t r th itx ' - ■ i ^ - i V: . I/O I 1 i f c , ACKNOWLEDGMENTS The s t u d y r e p o r t e d h e r e i s s p a r t o f a l a r g e r r e s e a r c h p r o j e c t b e i n g o o n d u c te d u n d e r C o n t r a c t Nonr 2 6I4.9 (0 0 ) v l t h t h e O f f i c e o f N av al R e s e a r c h . The r e s e a r c h was s u p p o r t e d b y th e B u re au o f S h i p s , t h e B u re au o f N aval W eapons, and th e B u re au o f N aval P e r s o n n e l i n a d d i t i o n t o th e O f f i c e o f N a v al R e s e a r c h . The w r i t e r i s i n d e b t e d t o t h e o f f i c e r s and men o f t h e T7. S . F l e e t A n t i - s u b m a r i n e W a r fa r e S c h o o l, San D ie g o , f o r t h e i r c o n t i n u e d c o o p e r a t i o n . I t i s a p l e a s u r e to e x p r e s s my i n d e b t e d n e s s t o my f e l l o w s t a f f members o f Human F a c t o r s R e s e a r c h , I n c o r p o r a t e d . Mr. A l b e r t H a r a b e d ia n , Mr. Edward P a r k e r , D r. D onald B u c k n e r, D r. W illia m H a r r i s , D r. D o u g la s H a r r i s , and D r. R o b e r t M ackie w ere e s p e c i a l l y g e n e r o u s w i t h t h e i r m o ra l and m a t e r i a l s u p p o r t . D r. F lo y d R uch, c h a ir m a n o f t h i s d i s s e r t a t i o n c o m m itte e , h a s b e e n g e n u i n e l y h e l p f u l and p e r f e c t i n h i s c o o p e r a t i o n and c o u n s e l t h r o u g h o u t th e s t a g e s o f t h i s i n v e s t i g a t i o n . 11 TABLE OF CONTENTS Page ACKNOWLEDGMENTS ............................................................................................ II LIST OF TABLES................................................................................................. v LIST OF F I G U R E S ............................................................................................ vl Chapter I . INTRODUCTION .................................................................................. 1 I I . DEVELOPMENT OF THE PROBLEM........................................... U Background The V ig i la n c e Decrement B r o a d b o n t's F i l t e r Theory The A rou sal Theory The E x p er im e n ta l H y p o th e sis I I I . A REVIEW OF THE LITERATURE............................................ 17 IV. EXPERIMENT I: EXTRANEOUS AUDITORY STIMULA TION AND VISUAL VIGILANCE ?? Method R e s u lt s V. EXPERIMENT I I : EXTRANEOUS VISUAL STIMULA TION AND AUDITORY VIGILANCE M e thod R e s u lt s VI. DISCUSSION...................................................................................... 60 I m p li c a t io n s fo r th e F i l t e r Theory I m p li c a t io n s f o r th e A ro u sal Theory An A r o u a a l - F l l t e r Theory S u g g e s t io n s fo r F u rth er R esearch ill C h a p te r Pag« V I I . SUMMARY............................................................................ 69 P u rp o se The P roblem The E x p e r i m e n t a l H y p o t h e s i s E x p e r im e n t I E x p e rim e n t I I C o n c lu s io n s REFERENCES............................................................................................. 76 APPENDIX I: P r e lim in a r y P s y c h o p h y s ic a l S t u d i e s . . 81 APPENDIX I I : S ig n a l P r e s e n t a t i o n S c h e d u le s . . . . 86 Iv LIST OF TABLES T ab le I. II. III. IV. V. VI. v i r. VI II. IX. Page Schedu le o f W atch stan ding S e s s io n s ...................... Number o f S i g n a ls O ccurring In 15-M lnute I n t e r v a l s on D i f f e r e n t S ig n a l P r e s e n t a t io n S c h e d u l e s ..................................................................................... 3ft D i s t r i b u t i o n o f I n t e r s i g n a l I n t e r v a l s . . . . Mean P er cen ta g e o f S i g n a ls D e te c te d as a F u n ctio n o f A u d ito ry C o n d itio n s and P r a c t i c e ..................................... I46 Analysis of Variance of Performance on the Visual Vigilance Task.................. Schedule of Experimental Conditions ......... n 7 Mean P ercen ta g e o f S ig n a ls D e te c te d as a F u n ctio n o f V isu a l C o n d itio n s and P r a c t i c e ..................................................................................... -ft A n a ly s is o f V ariance o f A u d itory W atchstand- in g P e r f o r m a n c e ..................................................................... Signal Presentation Schelnlos ................ Q7 v LIST OF FIGURES F i g u r e s Peg® 1 . Mean P e r c e n ta g e o f S i g n a l s D e te c te d on V isu a l and A u d ito ry V i g i l a n c e Tasks as a F u n c tio n o f Time on Watch, N » 5 U ................................................. 9 2 . Type o f S ig n a l Used in th e E xp erim ental T a s k ...................................................................................................... 2^ 3 . Sch em atic Diagram o f th e E xp erim en tal A p p a r a t u s ...................................................................................... 27 1|. Layout o f E x p erim en ta l F a c i l i t i e s ............................. ?Q U. P er ce n ta g e o f S i g n a l s D e te c te d on a V isu a l V ig i la n c e Task as a F u n c tio n o f Time on Watch (N - 2 8 ) .............................................................................. 1,3 6 . P e r c e n ta g e o f S i g n a l s D e te c te d on a V is u a l V i g i l a n c e Task a s a F u n c tio n o f Time on Watch fo r Two C o n d itio n s o f I r r e l e v a n t A u d ito ry S t i m u l a t i o n (N « 2 8 ) ................................. 1*0 7. Mean Number o f F a ls e D e t e c t i o n s on a V is u a l V i g i la n c e Task as a F u n c tio n o f Time on Watch under Two C o n d itio n s o f E xtran eou s A u d ito ry S t i m u l a t i o n (N ■ 2 8 ) ^1 3 . P erce n ta g e o f S i g n a ls D e te c te d on a V is u a l V i g i la n c e Task on S u c c e s s i v e Days o f Watch- s t a n d in g (N • 2 8 ) ................................................................. I 4? 0. Mean Number o f F a ls e D e t e c t i o n s R eported on S u c c e s s i v e Days o f V isu a l W atch stan d in g (N - 2 8 ) ............................................................................................ U3 10. P e r c e n ta g e o f S i g n a l s D e te c te d on a V isu a l V i g i la n c e Task by li| Sonarmen and 1I 4 Casual P er so n n e l a s a F u n c tio n o f Time on Watch . „ /, L 11. Layout o f W a tch stan d in g B ooth s, Experim ent I I ............................................................................................ r\ v i F ig u r e Page IP. P e r c e n ta g e o f S i g n a l s D e te c te d on an A u d itory V i g i la n c e Task as a F u n c tio n o f Time on Watch (N - 1 8 ) ............................................................................ Sh 1 3 . P e r c e n ta g e o f S i g n a l s D e te c te d on an A u d ito ry V i g i la n c e Task as a F u n c tio n o f Time on Watch under Two C o n d itio n s o f V is u a l S t im u la t io n (N ■ 1 8 ) ............................................................. 56 l i |. Mean Number o f F a ls e D e t e c t i o n s on an A u d ito ry V i g i la n c e Task a s a F u n c tio n o f Time on Watch under Two C o n d itio n s o f V isu a l S t i m u la t io n (N - 1 8 ) ........................................................... ?7 15. Time Spent L ooking a t Albums and D i f f e r e n c e in P er ce n ta g e o f D e t e c t io n s on V a r ie ty and C on tro l Watches as a F u n c tio n o f Time on Watch (N a 1 8 ) ........................................................................... 65 1 6 . Mean Per Cent C o rrect B r ig h t n e s s D is c r im in a t i o n s as a F u n c tio n o f I n t e n s i t y o f the Comparison S tim u lu s Showing E x t r a p o la t io n to th e 90% S i g n a l D e t e c t io n L ev el fo r ll+ Sonarmen and II4 . Casual P er so n n e l . . . . 17 . Mean Per Cent C o r re ct Loudness D i s c r i m i n a t i o n s as a F u n c tio n o f I n t e n s i t y of the Comparison S tim u lu s fo r 18 S o n a r m e n ................................................. ^ v i l CHAPTER I INTRODUCTION Man I s a p o o r m o n i t o r . T h is d i s t u r b i n g c o n c l u s i o n •m erg ad from t h e s t u d y o f r a d a r w a t c h s t a n d i n g by th e B r i t i s h in World War I I , and h a s a in o e b e en v e r i f i e d by num erous i n v e s t i g a t o r s i n t h i s c o u n t r y . I t h a s b een r e p e a t e d l y d e m o n s tr a te d t h a t human o b s e r v e r s when r e q u i r e d t o m a i n t a i n a t t e n t i v e w a tc h f o r p r o lo n g e d p e r i o d s o f tim e t y p i c a l l y s u f f e r a l o s s i n d e t e c t i o n e f f i c i e n c y as th e w a tc h p r o g r e s s e s . The i m p l i c a t i o n s o f t h i s f i n d i n g can be r e c o g n i z e d i n t h e r o l e o f man i n m odern m i l i t a r y and i n d u s t r i a l s y s te m s . T hese s y s te m s show two s i g n i f i c a n t t r e n d s : th e y a r e becom ing more co m p lex , and th e y a re becom ing more a u t o m a t i c . As a r e s u l t , m a n 's f u n c t i o n in th e sy s te m h as be en c h a n g in g from t h a t o f an a c t i v e o p e r a t o r and c o n t r o l l e r t o t h a t o f a p a s s i v e o v e r s e e r o f a u to m a te d e q u ip m e n t whose job i s to d e t e o t c h a n g e s i n th e sy s te m o u t p u t . Many o f th e v i t a l m i s s i o n s o f m i l i t a r y sy s te m s r e q u i r e v i g i l a n t o b s e r v e r s . Our n a t i o n a l s e c u r i t y i s now h e a v i l y d e p e n d e n t upon th e e f f i c i e n c y o f m i s s i l e d e t e c t i o n 1 2 and e a r l y w a r n in g s y s t e m s . Howland ( i 9 6 0 ) haa n o t e d t h a t t h e human m o n i t o r may aoon be a k e y f i g u r e In w o rld a f f a i r e , a l n c e any a g re e m e n t t o d la a r m o r t o ban n u c l e a r w eapona t e a t l n g w i l l r e q u i r e s u r v e i l l a n c e orewa and m o n i t o r s o f r a d i o l o g i c a l o r s e i s m i c d e t e c t i o n d e v i c e s . And, s u r e ly , when man v e n tu r e s In to space he w i l l do so as a m onitor o f an automated v e h i c l e . The s t e a d i l y c h a n g in g r o l e o f t h e human o p e r a t o r In c o m p lex , a u to m a te d m i l i t a r y and I n d u s t r i a l s y s te m s h a s s p u r r e d a r e s e a r c h e f f o r t t h a t h a s I n c r e a s e d I n m a g n itu d e and sc o p e a t an a c c e l e r a t i n g r a t e . T h is e f f o r t h a s b e e n d i r e c t e d m a in ly a t i d e n t i f y i n g th e v a r i a b l e s t h a t a f f e c t th e " v i g i l a n c e d e c r e m e n t ." Much o f th e e x p e r i m e n t a t i o n h a a b e e n d e s i g n e d to p r o v i d e a n s w e rs to s p e c i f i c p r a c t i c a l q u e s t i o n s , and t h e r e s u l t h a a b e e n a m ass o f e m p i r i c a l d a t a from a v a r i e t y o f e x p e r i m e n t a l s i t u a t i o n s . In an e f f o r t t o b r i n g o r d e r and u n d e r s t a n d i n g t o t h e s e a c c u m u la te d e m p i r i o a l f i n d i n g s , s e v e r a l I n v e s t i g a t o r s h a v e a t t e m p t e d t o d e v i s e s u i t a b l e t h e o r e t i c a l m o d els to a c c o u n t f o r them . G e n e r a l l y , th e t h e o r i e s have b een fram e w o rk s f o r p o s s i b l e e x p l a n a t i o n s o f p r e s e n t l y a v a i l a b le d a t a and h a v e b e e n c o n s p i c u o u s l y d e l i n q u e n t In p r o v i d i n g new h y p o t h e s e s and p r e d i c t i o n s t h a t w i l l a llo w them t o b e e m p i r i c a l l y e v a l u a t e d . F u r t h e r p r o g r e s s In d e v e l o p i n g a r i g o r o u s t h e o r y o f v i g i l a n c e a w a i t s a t l e a s t 3 two p r e l i m i n a r y s t e p s : th e d e r i v a t i o n o f s p e c i f i c p r e d i c t i o n s from th e v a r i o u s c o n te m p o r a r y t h e o r i e s and th e e m p i r i c a l t e s t i n g o f t h e s e p r e d i c t i o n s . The r e s e a r c h r e p o r t e d h e r e was d e s i g n e d as a t e s t o f o p p o s in g p r e d i c t i o n s d e r i v e d from two d i f f e r e n t t h e o r i e s o f v i g i l a n c e . The e x p e r i m e n t a l s i t u a t i o n i n v o lv e d w a t c h s t a n d i n g i n an e n v iro n m e n t c o n t a i n i n g a s o u r c e o f i r r e l e v a n t s t i m u l a t i o n c o m p e tin g w i t h th e s o u r c e o f s i g n a l s t o be d e t e c t e d com pared w ith w a t c h s t a n d i n g In th e a b s e n c e o f c o m p e tin g s t i m u l a t i o n . One p r e d i c t i o n , d e r i v e d by th e p r e s e n t w r i t e r from a " f i l t e r " t h e o r y o f v i g i l a n c e a s p ro p o se d by B ro a d b e n t ( 1 9 5 8 ) , was th a t th e c o m p e tin g s t i m u l a t i o n w ould r e d u c e th e p r o b a b i l i t y o f d e t e c t i n g c r i t i c a l s i g n a l s . The o t h e r p r e d i c t i o n , d e r i v e d by th e p r e s e n t w r i t e r from an " a r o u s a l " t h e o r y b a a e d on th e t h e s e s o f Hebb ( 1 9 5 5 ) , was t h a t th e c o m p e tin g s t i m u l a t i o n would f u l f i l l th e o b s e r v e r ’ s r e q u i r e m e n t f o r s e n s o r y v a r i a t i o n and t h e r e f o r e s e r v e t o Im prove v i g i l a n c e p e rf o rm a n c e . A d e t a i l e d s t a t e m e n t o f th e d e r i v a t i o n o f t h e s e p r e d i c t i o n s I s c o n t a i n e d In C h a p te r I I o f t h i s r e p o r t . C h a p te r I I I c o n t a i n s a summary o f th e r e l e v a n t l i t e r a t u r e . The i n v e s t i g a t i o n was c a r r i e d o u t In two p h a s e s . In t h e f i r s t p h a s e , d e s o r l b e d i n C h a p te r IV, an e x p e r im e n t was c o n d u c te d to t e a t th e e f f e c t s o f e x t r a n e o u s a u d lto r Y k s t i m u l a t i o n on v i s u a l v i g i l a n c e p e rf o r m a n c e . In th e seoon d phase* d e s c r i b e d i n C h a p te r V, an e x p e r im e n t was c o n d u c te d t o t e s t th e e f f e c t s o f e x t r a n e o u s v i s u a l s t i m u l a t i o n on a u d i t o r y v i g l l a n e e p e r f o r m a n c e . The I m p l i c a t i o n s o f th e e x p e r i m e n t a l f i n d i n g s a r e d i s c u s s e d * some c o n c l u s i o n s a r e drawn* and some recom mend a t i o n s a r e o f f e r e d i n C h a p te r VI. The r e s e a r c h I s sum m arized In th e f i n a l c h a p t e r . CHAPTER I I DEVELOPMENT OF THE PROBLEM The p ro b le m c o n c e r n s th e d e c r e m e n t In human p e rf o r m a n c e on v i g i l a n c e t a s k s * Some b a c k g ro u n d I n f o r m a t i o n on v i g i l a n c e p e rf o r m a n c e w i l l be p r e s e n t e d f i r s t In t h i s c h a p t e r , a d e s c r i p t i o n o f th e " f i l t e r '1 and " a r o u s a l " t h e o r i e s o f v i g i l a n c e w i l l f o l l o w , and t h e n th e e x p e r i m e n ta l h y p o t h e s i s w i l l be d e r i v e d . B ack g ro u n d The m ea n in g o f th e term " v i g i l a n c e " h a s been am biguous In t h e l i t e r a t u r e . I t h a s so m e tim e s r e f e r r e d t o a c e n t r a l p r o c e s s d e t e r m i n i n g p e rf o r m a n c e on c e r t a i n ty p e s o f t a s k s a s In M a c k w o rth Ts (1 9 5 7 ) d e f i n i t i o n : " . . . th e term v i g i l a n c e c o u ld be r e g a r d e d a s m e a n in g ' a s t a t e o f r e a d i n e s s to d e t e c t and re s p o n d to c e r t a i n s p e c i f i e d s m a ll c h a n g e s o c o u r r l n g a t random tim e I n t e r v a l s I n t h e e n v i r o n m e n t . " From a n o t h e r p o i n t o f view ( H o l l a n d , 195^) I t I s u n s a t l s f a c t o r y to s p e a k o f s u b j e c t i v e s t a t e s when t h e s e s t a t e s can o n ly be I n f e r r e d from o b s e r v a b l e p e r f o r m a n c e ; and th e te r m " v i g i l a n c e " I s t a k e n as r e f e r r i n g to t h e o b s e r v a b l e r e s p o n s e b e h a v i o r o f an o b s e r v e r on a 5 6 w a t c h s t a n d i n g t a s k . M cG rath, H a r a b e d ia n , and B uokner (1 9 5 9 ) p r e f e r r e d t o u s e " v i g i l a n c e " a s a c o n v e n i e n t l a b e l t o f a c i l i t a t e d i s c o u r s e on t h e p ro b le m o f human w a t c h s t e n d i n g , and to s p e c i f y t h e t a s k c o n d i t i o n s u n d e r w h ioh v i g i l a n c e p e r f o r m a n c e i s o b s e r v e d . They s p e c i f i e d th e f o l l o w i n g : 1. A d e t e c t i o n t a s k i s i n v o l v e d , a t a s k i n w h ic h an o b s e r v e r i s r e q u i r e d t o p e r c e i v e and r e p o r t th e p r e s e n o e o r a b s e n c e o f some s p e c i f i e d c h a n g e (a s i g n a l " ) i n h i s o p e r a t i n g e n v ir o n m e n t . 2 . The s i g n a l t o be d e t e c t e d may be e i t h e r a d i s c r e t e s t i m u l u s added t o o r t a k e n away from t h e e n v i r o n m ent o r a c h an g e I n a c o n t i n u o u s l y p r e s e n t e d s t i m u l u s . . . . t h e s i g n a l s h o u ld b e d e t e c t a b l e u n d e r m om entary a l e r t e d c o n d i t i o n s , b u t . . . s h o u ld n o t in d u c e i n v o l u n t a r y a t t e n t i o n i n th e o b s e r v e r . 3 . The tim e o f s i g n a l p r e s e n t a t i o n m u st n o t be p r e d i c t a b l e b y t h e o b s e r v e r . The s p a t i a l l o c a t i o n o f t h e s i g n a l may o r may n o t be p r e d i c t a b l e . ij.. Ifae t a s k s h o u ld be a p r o l o n g e d , c o n t i n u o u s one P e rfo rm a n c e on v i g i l a n c e t a s k s h a s b e e n measured i n a v a r i e t y o f w ay s. The m o st t y p i c a l i n d i c e s o f v i g i l a n c e p e r f o r m a n c e a r e : P r o b a b i l i t y o f d e t e c t i o n . The p r o b a b i l i t y o f s i g n a l d e t e c t i o n I s u s u a l l y i n f e r r e d fro m t h e p e r c e n t a g e o f s i g n a l s d e t e c t e d d u r i n g some tim e p e r i o d o r fro m t h e p e r c e n t a g e o f o b s e r v e r s d e t e c t i n g a g i v e n s i g n a l . L a te n c y o f r e s p o n s e . The tim e l a p s e b e tw e e n s i g n a l p r e s e n t a t i o n and t h e o b s e r v e r ' s r e s p o n s e h a s b e e n u s e d a s a p e r f o r m a n c e m e a su re when t h e s i g n a l was n o t t r a n s i t o r y , b u t p e r s i s t e d u n t i l d e t e c t e d . 7 T h r e s h o ld m e a s u r e s . Changes i n a b s o l u t e o r d i f f e r e n c e t h r e s h o l d s h av e b e e n o b t a i n e d a s v i g i l a n c e p e rfo r m a n c e m e a s u r e s . The u s u a l method I s to f i n d th e I n t e n s i t y t o w h ic h a g i v e n s i g n a l h a s to be I n c r e a s e d b e f o r e I t I s d e t e c t e d . The V i g i l a n c e D ecrem ent I n v e s t i g a t o r s o f v i g i l a n c e p e rfo rm a n c e h av e d i r e c t e d m o st o f t h e i r e f f o r t s to w a rd I d e n t i f y i n g th e v a r i a b l e s a f f e c t i n g th e c h a r a c t e r i s t i c d e c l i n e I n d e t e c t i o n e f f i c i e n c y d u r i n g p r o lo n g e d w a t c h s t a n d i n g . T h is d e o l l n e h a s beoome known as t h e " v l g l l a n o e d e c re m e n t" and h a s b e e n d e m o n s tr a te d u s i n g p r o b a b i l i t y o f d e t e c t i o n (Adams, 1 95&; B a k e r, 195®; B u o k n er, H a r a b e d ia n , and M cG rath, 19&0; D eese and Ormond, 1953# H o lla n d , 195®; J e n k i n s , 1959# J « r i s o n , 195®# K appauf and Powe, 1959; M ackw orth, 1950; and W l t t e n b u r g , R oss and A ndrew s, 1956)# l a t e n c y o f r e s p o n s e (G a rv e y , T a y l o r , and N e w lin , 1959; McCormack, 195®)# end t h r e s h o l d m e a s u re s (B akan, 1955; G arv ey , Henson, and O u lle d g e , 195®; M c F a rlan d , Holway, and H u rv lc h , 19^2# S o l a n d t and P a r t r i d g e , 191+6) • The r e f e r e n c e s a r e by no means e x h a u s t i v e and a r e in te n d e d m e r e ly to be r e p r e s e n t a t i v e . The p r e s e n t i n v e s t i g a t o r and h i s a s s o c i a t e s have r e c e n t l y p r o v id e d e ls e w h e r e an e x t e n s i v e re v ie w and c r i t i q u e o f th e l i t e r a t u r e on v i g i l a n c e p e rfo rm a n c e (M cG rath, e t a l . , 1 9 5 9 ). T h is re v ie w w i l l n o t be r ep ea ted h e r e , b u t th e r e s u l t s o f a r e p r e s e n t a t i v e stu d y w i l l be Q shown t h a t I l l u s t r a t e t h e v i g i l a n c e d e c r e m e n t, B u c k n e r, e t a l . ( i 9 6 0 ) c o n d u c te d a s t u d y o f I n d i v i d u a l d i f f e r e n c e s i n v i g i l a n c e p e rf o rm a n c e i n w hich f i f t y - f o u r Ss each s to o d 16 o n e - h o u r w a tc h e s on an a u d i t o r y v i g i l a n c e t a s k and 16 o n e - h o u r w a tc h e s on a v i s u a l v i g i l a n c e t a s k , (T h ese t a s k s w e re u se d i n th e p r e s e n t s t u d y and a r e d e s c r i b e d i n d e t a i l i n C h a p te r s IV and V o f t h i s r e p o r t , ) Im m e d ia te ly b e f o r e and a f t e r t h e o n e - h o u r w a tc h e s t h e Ss w ere g i v e n b r i e f p r e t e s t s and p o s t t e s t s to e s t a b l i s h th e d e t e c t a b i l i t y o f t h e s i g n a l s u n d e r a l e r t e d c o n d i t i o n s . The r e s u l t s a r e shown i n F ig u r e 1. I t w i l l be n o te d t h a t t h e r e was a s h a r p d e c l i n e in d e t e c t i o n e f f i c i e n c y from th e p r e t e s t to t h e b e g i n n i n g o f th e w a tc h . D u rin g th e w a tc h p e rfo rm a n c e c o n ti n u e d t o d e c l i n e , r a p i d l y a t f i r s t and t h e n l e v e l i n g o f f som ewhat w i t h an "end s p u r t " a t th e c l o s e o f v i s u a l w a t c h e s . At t h e end o f t h e w a tc h th e p o s t t e a t was g i v e n and p e rfo rm a n c e r e c o v e r e d a b r u p t l y and c o m p l e t e ly to th e p r e t e s t l e v e l . I t w i l l f u r t h e r be n o t e d t h a t t h e v i g i l a n c e d e c re m e n t was e s s e n t i a l l y th e seme f o r th e v i s u a l and th e a u d i t o r y t a s k s . The p e rfo rm a n c e t r e n d s shown i n F ig u r e 1 a r e t y p i c a l o f th e r e s u l t s o f v i g i l a n c e s t u d i e s . I t i s t h i s d e c l i n e i n d e t e c t i o n e f f i c i e n c y a s a f u n c t i o n o f tim e on w a tc h t h a t v l g i l a n o e t h e o r i e s h a v e s o u g h t to e x p l a i n . A ll o f t h e c o n te m p o ra ry t h e o r i e s o f v i g i l a n c e have been PERCENTAGE O F SIGNALS DETECTED 0 100 8 0 (- 6 0 - • ■« V isu a l o Auditory 7 0 i- \ X x o 90h j,qL i i i i j i i i i i 1 ‘ ‘ 1 o i o po 30 lo oo 6o Pro Post t o s t VIN1JTK3 OF '.V A T C M t o s t F ig u re 1 , Mean p e r c e n ta g e o f s i g n a l s d e t e c t e d on v i s u a l and a u d ito r y v i g i l a n c e ta s k s as a f u n c t i o n of tim e on w atch, N = 5U* (Buckner, e t a l . , i 9 6 0 ) . 10 d e s c r i b e d e ls e w h e r e (F rankm ann and Adams, 19&0; M cG rath, e t a l . , 1959)* Only th e two t h e o r i e s r e l e v a n t t o t h i s I n v e s t i g a t i o n w i l l be d e s o r i b e d h e r e . B r o a d b e n t fs F i l t e r T h e o ry B ro a d b e n t (1953** 1953b, 1 957, 1958) o f f e r e d a t h e o r y o f v i g i l a n c e b a s e d on th e I n f o r m a t i o n p r o c e s s i n g c h a r a c t e r i s t i c s o f th e human p e r c e p t u a l s y s te m . The t h e o r y was d e s i g n e d t o e x p l a i n th e f a c t s o f c l a s s i c a l c o n d i t i o n i n g and p e r f o r m a n c e on r e p e t i t i v e t a s k s , b u t i t w i l l be r e l a t e d o n l y to th e f a c t s o f v i g i l a n c e p e rf o r m a n c e i n t h i s d i s c u s s i o n . The human p e r o e p t u a l s y s te m Is assum ed to have a l i m i t e d c a p a c i t y and t h u s to be I n c a p a b l e o f a n a l y s i n g s i m u l t a n e o u s l y a l l t h e i n f o r m a t i o n r e c e i v e d by t h e s e n s e o r g a n s . Of t h e t o t a l s t i m u l a t i o n im p in g in g upon th e o r g a n is m a t any g iv e n tim e o n ly p a r t I s c a p a b le o f i n i t i a t i n g a r e s p o n s e . B ro a d b e n t m a i n t a i n e d t h a t " . . . a d e q u a te r e s p o n s e t o one p a r t o f th e s t i m u l u s s i t u a t i o n i s i n c o m p a t i b l e w i t h a d e q u a te r e s p o n s e t o sm o th e r p a r t . ” In c o n s e q u e n c e a s e l e c t i v e o p e r a t i o n l a p e rfo rm e d upon a l l I n p u t s to t h e s y s te m . A " f i l t e r ' ’ p l a c e d e a r l y i n th e n e r v o u s s y s te m s e l e c t s o n l y p a r t o f t h e i n f o r m a t i o n a v a i l a b le from th e r e c e p t o r s and p a s s e s t h i s on t o th e p e r c e p t u a l s y s te m . N orm ally, the f i l t e r s e l e c t s n e c e s s a r y or r e l e v a n t 11 I n f o r m a t i o n f o r t h e t a s k a t h a n d ; so t h a t i n p e r f o r m i n g a v i g i l a n c e t a s k I n f o r m a t i o n w i l l be s e l e c t e d p r i m a r i l y from t h e s i g n a l - p r o d u c i n g d i s p l a y . The f i l t e r h a s a p e rm a n e n t b i a s , h o w e v e r, i n f a v o r o f c h a n n e ls w h ic h have n o t r e c e n t l y b e e n a o t l v e . T h u s, a f t e r c o n ti n u o u s o b s e r v a t i o n o f one s o u r c e o f i n f o r m a t i o n , t h e f i l t e r w i l l s e l e c t i n f o r m a t i o n from o t h e r s o u r c e s , "S u c h b r e a k s i n th e i n t a k e o f t a s k i n f o r m a t i o n w i l l be b r i e f , " B ro a d b e n t p r o p o s e d , " b u t w i l l l n o r e a s e i n f r e q u e n c y a s t h e t a s k i s o o n t l n u e d . One m ig h t t h e r e f o r e e x p l a i n v i g i l a n c e d e c re m e n t by s u p p o s in g t h a t th e s i g n a l s a r r i v i n g l a t e r i n th e t a s k a r e more l i k e l y to f a l l in t h e s e b r i e f I n s t a n t s and so be m i s s e d ." B ro a d b e n t f u r t h e r a s s e r t e d , " C e r t a i n p r o p e r t i e s o f a s t i m u l u s w i l l make i t more l i k e l y to be s e l e c t e d from among i t s c o m p e t i t o r s , and t o r e t a i n i t s dom inance i f s e l e c t e d by c h a n c e . " T hese p r o p e r t i e s a r e p h y s l o a l I n t e n s i t y , b i o l o g i c a l I m p o r t a n c e , and n o v e l t y . I t i s th e l a t t e r t h a t B ro a d b e n t e m p h a size d i n e x p l a i n i n g th e r e s u l t s o f v i g i l a n c e e x p e r i m e n t s . As t h e tim e o f a m onotonous w atch i s e x te n d e d , th e r e p e t i t i o u s s t i m u l i from t h e v i g i l a n c e d i s p l a y l o s e t h e i r n o v e l t y and a c c o r d i n g l y a r e l e s s l i k e l y t o be s e l e c t e d . I n i t i a l l y n e g l e c t e d s o u r c e s o f i n f o r m a t i o n w i l l become f a v o r e d , and s t i m u l i from th e r e m a in d e r o f t h e e n v iro n m e n t w i l l te n d to d o m in a te th e t a s k s t i m u l i . The s e l e c t i o n o f i r r e l e v a n t I n f o r m a t io n 12 a llo w s the* t a s k s t i m u l i to r e g a i n n o v e l t y , and the a p p r o p r i a t e m o n i t o r i n g I s re s u m e d . T h is c y c l e c f e v e n t s o c c u r s w i t h g r e a t e r f r e q u e n c y as th e w a tc h p r o g r e s s e s . In b r i e f , th e f i l t e r t h e o r y s t a t e s t h a t b e c a u s e o f th e l i m i t e d c a p a c i t y o f t h e human p e r c e p t u a l sy ste m a s e l e c t i v e o p e r a t i o n I s p e rfo rm e d on a l l I n p u t s t o t h a t s y s te m . D u rin g w a t c h s t a n d i n g on a v i g i l a n c e t a s k , th e o b s e r v e r w i l l s e l e c t I r r e l e v a n t c o m p e tin g s t i m u l i w i t h I n c r e a s i n g f r e q u e n c y as tim e on w atch p r o g r e s s e s . The r e s u l t w i l l be a d e c l i n e I n t h e p e r c e n t a g e o f s i g n a l s d e t e c t e d - - t h e v i g i l a n c e d e c r e m e n t. The A ro u s a l T heory N e u r o p h y s l o l o g i c a l r e s e a r c h (M oruzzl and Magoun, 1 9 q 9 * S a m u e ls, 19£9) h a s I n d i c a t e d t h a t s e n s o r y Im p u ls e s r e a c h th e c o r t e x th r o u g h two r o u t e s . The f i r s t pathw ay I s a lo n g t h e s e n s o r y t r a c t to t h e a p p r o p r i a t e th a la m ic c e n t e r and th e n c e d i r e c t l y to one o f th e s e n s o r y p r o j e c t i o n a r e a s of t h e c o r t e x . The seco n d pathw ay Is a lo n g a r a m b lin g I n d i r e c t r o u t e t h r o u g h th e a s c e n d i n g r e t i c u l a r f o r m a t i o n , th e n o n s p e c i f i c o r d i f f u s e p r o j e c t i o n sy ste m w h ich bom bards l a r g e a r e a s o f t h e c o r t e x w i t h a f f e r e n t I m p u ls e s . Hebb ( 1 9 5 5 ) p ro p o s e d t h a t a f f e r e n t im p u ls e s s e r v e two q u i t e d i f f e r e n t f u n c t i o n s as a r e s u l t o f t h e s e two d i f f e r e n t p a th w ay s to th e c o r t e x . The d i r e c t r o u t e s e r v e s 13 a cue f u n c t i o n , g u i d i n g and c o n t r o l l i n g b e h a v i o r t h r o u g h t h e e f f i c i e n t t r a n s m i s s i o n o f i n f o r m a t i o n . The c i r c u i t o u s r o u t e p r o d u c in g d i f f u s e bom bardm ent o f c o r t i c a l a r e a s s e r v e s an a r o u s a l o r v i g i l a n c e f u n c t i o n . " t o n i n g u p ” th e c o r t e x w i t h a b a c k g ro u n d o f s u p p o r t i n g a c t i v i t y . The a r o u s a l f u n o t l o n I s assum ed t o be c o m p le te ly n e c e s s a r y f o r o r g a n i s e d c o r t i c a l a c t i v i t y . " W ith o u t a f o u n d a t i o n o f a r o u s a l , " Hebb s a i d , " t h e cue f u n c t i o n c a n n o t e x i s t . " T hus, th e b r a i n i s assum ed t o r e q u i r e a c e r t a i n l e v e l o f n o n s p e c l f l o s t i m u l a t i o n t o make optimum u se o f th e c u e s upon w h ich e f f i c i e n t b e h a v i o r d e p e n d s . The a r o u s a l f u n c t i o n , i n t u r n , i s assumed to depend upon th e v a r i a b i l i t y o f th e s t i m u l u s s i t u a t i o n . Hebb (1 958 ) a s s e r t e d t h a t The n o rm al v a r i e t y o f s e n s o r y s t i m u l a t i o n h a s t h e f u n c t i o n o f m a i n t a i n i n g a r o u s a l : th e a l e r t n e s s , r e s p o n s i v e n e s s , o r " v i g i l a n c e " o f th e w a k in g s u b j e c t . When th e s t i m u l a t i o n i s made d r a s t i c a l l y m o n o to n o u s, m e n ta l f u n c t i o n i s s i g n i f i c a n t l y a f f e c t e d . The monotony o f th e s t i m u l u s c o n d i t i o n s i n a t y p i c a l v i g i l a n c e t a s k , t h e n , w ould l e a d to lo w e re d a r o u s a l , and th u s t o l e s s e f f i c i e n t d e t e c t i o n . Deese (1959) h a s made t h i s h y p o t h e s i s somewhat more e x p l i c i t w i t h r e g a r d to v i g i l a n c e p e r f o r m a n c e . He s a i d , "The m a in te n a n c e o f a g iv e n l e v e l o f v i g i l a n c e in an o b s e r v e r d e p en d s t o some e x t e n t upon s t i m u l u s e v e n t s e x t r i n s i c t o t h e o b s e r v e r . " The p ro b le m o f m a i n t a i n i n g 14 a l e r t n e s s under monotonous c o n d i t i o n s was view ed by Deese as a problem In m ain ten an ce o f a background se n s o r y Input t o o f f s e t th e d i s s i p a t i o n o f an i n i t i a l e x c i t a t o r y s t a t e o f v i g i l a n c e . The E x p e r im e n ta l H y p o th e s is I t I s c l e a r t h a t b o th th e f i l t e r and a r o u s a l t h e o r i e s o f v i g i l a n c e would p r e d i c t a decrem ent in d e t e c t i o n perform ance under p r o lo n g e d , monotonous w a tc h s ta n d in g c o n d i t i o n s . The p r e d i c t i o n o f the v i g i l a n c e decrem ent d e r iv e d from th e f i l t e r th e o r y i s based on th e assum ption t h a t th e o b s e r v e r w i l l tend more and more t o s e l e c t I r r e l e v a n t , com p etin g in fo r m a tio n as time on watch p r o g r e s s e s . The p r e d i c t i o n o f th e v i g i l a n c e decrem ent from th e a r o u s a l th e o r y I s based on th e assum p tion th a t c o n s t a n t , monotonous s t im u lu s c o n d i t i o n s w i l l le a d to a lo w e r in g o f c o r t i c a l a r o u sa l and th u s to l e s s e f f i c i e n t r e sp o n d in g . I t f o l l o w s from th e t h e o r e t i c a l m o d els, however, t h a t co m p etin g, e x tr a n e o u s s t i m u l a t i o n in th e w a tc h sta n d in g en viron m en t would be p r e d ic t e d to have q u it e o p p o s it e e f f e c t s , d epend ing upon the th e o r y from w hich th e p r e d i c t i o n was d e r iv e d . I t can be deduced from th e f i l t e r theory t h a t the fr e q u e n c y o f "ohannel sw itc h in g " w i l l in c r e a s e when n o v e l , i r r e l e v a n t in fo r m a tio n com petes w ith monotonous ta sk in f o r m a tio n , and thu s s i g n a l s would be more l i k e l y 1 5 t o be m isse d than in th e a b se n c e o f such c o m p e t it io n . On th e o th e r hand, i t can be deduced from th e a r o u s a l th e o r y t h a t n o v e l , i r r e l e v a n t in fo r m a tio n would I n c r e a s e th e t o t a l v a r i a b i l i t y o f th e s t im u lu s s i t u a t i o n ; t h i s would r a i s e the l e v e l o f c o r t i c a l a r o u s a l , and d e t e c t i o n e f f i c i e n c y would be Im proved. The r e s e a r c h r e p o r te d h ere was d e s ig n e d to c l a r i f y t h i s i s s u e and to d e ter m in e w hich p r e d i c t i o n would be supported* The p r e s e n t i n v e s t i g a t o r has found th e a r o u s a l th e o r y t o be more c o n v in c in g , and t h e r e f o r e fa v o r e d th e p r e d i c t i o n d e r iv e d from t h a t t h e o r y . B ecause o f t h i s , the e x p e r im e n ta l h y p o t h e s i s i s s t a t e d h ere in term s o f th e p r e d i c t i o n from th e a r o u s a l t h e o r y . The h y p o t h e s is t e s t e d in t h i s s t u d y was: W a tch stan d ers w i l l d e t e c t a g r e a t e r p e r c e n ta g e o f s i g n a l s when a v a r i e t y o f s t i m u l a t i o n i s p r e s e n t in the en viron m en t than in the a b sen ce o f such v a r i e t y , even though the in c r e a s e d v a r i a b i l i t y haa no r e l e v a n c e f o r th e v i g i l a n c e ta s k b e in g perform ed . The a l t e r n a t i v e h y p o t h e s i s , deduced from th e f i l t e r t h e o r y , i s t h a t th e I n c r e a s e d v a r i e t y w i l l produce an added decrem ent in th e p e r c e n ta g e o f s i g n a l s d e t e c t e d d u r in g w a tc h s ta n d in g . A t h ir d a l t e r n a t i v e i s t h a t th e r e w i l l be no d i f f e r e n c e in v i g i l a n c e perform ance under the two c o n d l c io n s . The h y p o t h e s is was t e s t e d in two w ays. F i r s t , the e f f e c t o f e x tr a n e o u s a u d lt o r y s t i m u l a t i o n on v i s u a l 1 6 v i g i l a n c e p e rfo rm a n c e was o b s e r v e d . S econd, th e e f f e c t o f e x t r a n e o u s v i s u a l s t i m u l a t i o n on a u d l t o r y v i g i l a n c e p e rfo rm a n c e was o b s e r v e d . CHAPTER I I I A REVIEW OF THE LITERATURE As s t a t e d e a r l i e r , a c o m p lete rev ie w o f th e l i t e r a t u r e on v i g i l a n c e p e rfo rm an c e has been p r e s e n t e d e ls e w h e r e (McGrath, e t a l . , 1959)* The s t u d i e s review ed i n t h i s c h a p t e r a re t h o s e which a re r e l e v a n t to th e a p p r a i s a l o f th e I n f l u e n c e o f e x tr a n e o u s e n v iro n m e n ta l s t i m u l a t i o n on v i g i l a n c e p e rfo rm a n c e . Only two such s t u d i e s have been r e p o r t e d In the l i t e r a t u r e . In a stu d y o f the i n f l u e n c e of m o t i v e - I n c e n t i v e c o n d i t i o n s on v i g i l a n c e p e rfo rm an c e P o lla c k and K n a ff ( 1 9 9 8 ) i n v e s t i g a t e d , as a m a t t e r o f se co n d a ry I n t e r e s t to them , the e f f e c t o f v a r i a t i o n i n th e amount of e n v i r o n m e n ta l s t i m u l a t i o n p r e s e n t d u r i n g w a te h a ta n d ln g . T h e ir 3s stoo d BO-minute w a tch e s u n d e r t h r e e d i f f e r e n t m o tiv e - i n c e n t i v e c o n d i t i o n s : n e u t r a l , rew ard , and p u n ishm en t. Under the n e u t r a l c o n d i t i o n the Ss were t o l d sim p ly " to do th e b e s t you c a n ." Under the rew ard c o n d i t i o n t h e y were t o l d t h a t th ey would r e c e i v e e x t r a pay f o r good p e rfo r m ance* Under th e punishm ent c o n d i t i o n , f a i l u r e to d e t e c t a s i g n a l was g r e e t e d by a h a l f - s e c o n d b l a s t (abo ut 115 d b ) o f a G eneral Motors C o r p o r a tio n t r u c k horn p la c e d n e a r th e 17 18 S ' s h ead. V a r i a t i o n In e x tr a n e o u s s t i m u l a t i o n was a c h ie v e d by h a r i n g th e Ss s ta n d w a tch u n d e r two d i f f e r e n t e n v ir o n m e n ta l c o n d i t i o n s : " d a rk " and " l i g h t . " In th e " d ark " e n v iro n m en t Ss worked i n i s o l a t i o n in a b o o th w h ich , e x o e p t f o r th e d i s p l a y , was d a rk e n e d . In th e " l i g h t " en v iro n m en t th e Ss worked i n th e company o f o t h e r s in a b r i g h t l y i l l u m i n a t e d room, a r a d i o p la y e d m o d e r a te ly loud p o p u la r m u sic , and c o n v e r s a t i o n ( e x c e p t a b o u t s i g n a l s ) was p e r m i t t e d . Each o b s e r v e r se rv e d f o r tw elve s e s s i o n s , two s e s s i o n s under each o f th e s i x p o s s i b l e c o n d i t i o n s . The t a s k o f the o b s e r v e r was to d e t e c t and r e p o r t a change in d e f l e c t i o n of t h e n e e d le of a m e te r from a p r e d i c t e d c o u r s e . These changes o c c u rr e d an averag e o f s i x t y - f o u r tim es d u r i n g an 80-m in u te w a tch . T here was no s i g n i f i c a n t d i f f e r e n c e betw een p e rfo rm an c e in th e l i g h t and d a rk e n v ir o n m e n ts . Under the punishm ent c o n d i t i o n t h e r e was a marked Improvement In the p e r c e n ta g e o f s i g n a l s d e t e c t e d . P erform ance was b e t t e r under th e rew ard c o n d i t i o n th a n tinder th e n e u t r a l c o n d i t i o n , b u t th e improvement was n o t as g r e a t as t h a t produced by p u n ish m en t. A s i g n i f i c a n t I n t e r a c t i o n a p p ea re d betw een th e m o t i v e - i n c e n t i v e c o n d i t i o n s and the e n v iro n m e n ta l c o n d i t i o n s : p u n ish m en t was more e f f e c t i v e i n th e d a rk and rew ard was more e f f e c t i v e In th e l i g h t . Perform ance under a l l c o n d i t i o n s c o n s i s t e n t l y d e c l i n e d as a f u n c t i o n o f tim e on w atch. 19 The r e s u l t s o f P o l l a c k and K n a f f 's s tu d y su p p o rte d n e i t h e r th e f i l t e r n o r th e a r o u s a l t h e o r y of v i g i l a n c e , s i n c e th e I r r e l e v a n t , co m p eting e n v ir o n m e n ta l s t i m u l a t i o n produced n e i t h e r an improvement n o r an added decrem ent In d e t e c t i o n p e rf o r m a n c e . The e f f e c t i v e n e s s o f th e t r u c k h o rn m ig h t be c o n s i d e r e d as s u p p o r t f o r th e a r o u s a l t h e o r y , s i n c e i t i n t r o d u c e d a d d i t i o n a l s t i m u l a t i o n i n t o th e e n v ir o n m e n t, w h ereas the rew ard and n e u t r a l c o n d i t i o n s d id n o t . However, th e t r u c k ho rn a l s o se rv e d as an In fo rm a t i o n a l sy ste m , n o t i f y i n g th e o b s e r v e r chat he m isse d a s i g n a l , and t h e r e b y p r o v i d i n g knowledge o f r e s u l t s . Immediate knowledge o f r e s u l t s has been shown to lmnrove v i g i l a n c e p e rfo rm a n c e (Mackworth, 1950 ). The t r u c k horn f u r t h e r se rv e d a s a p un ish m ent sy ste m , j o l t i n g th e o b s e r v e r f o r f a i l u r e to d e t e c t the s i g n a l . P o l l a c k and K naff a re p r e s e n t l y u n d e r t a k i n g a s e r i e s o f t e s t s to ra n k th e im p o rta n c e o f th e t h r e e f u n c t i o n s o f th e t r u c k horn. P r e l i m i n a r y (u n p u b lis h e d ) r e s u l t s of t h e s e t e s t s I n d i c a t e d t h a t th e "p u nishm ent" and " i n f o r m a t i o n a l " f u n c t i o n s were more i m p o r t a n t th a n th e " a r o u s a l " f u n c t i o n . A lthough th e " l l g h t f and "d ark " e n v iro n m e n ts did n o t pro du ce d i f f e r e n c e s in p e rfo rm a n c e in P o lla c k and K n a f f 's s t u d y , one o f th e d i f f e r e n c e s in t h e s e e n v lr o n - m e n ta - - w o rk in g in i s o l a t i o n v e r s u s w orkin g In th e company o f o t h e r s - - h a s been shown to a f f e c t v i g i l a n c e p e r f o r m a n c e . 20 F r a s e r (1953) s t u d i e d th e I n f l u e n c e on v i g i l a n c e p e r f o r m ance o f th e p r e s e n o e o r a b s e n c e o f t h e e x p e r i m e n t e r In th e w a t e h s t a n d l n g e n v ir o n m e n t. The t a s k r e q u i r e d th e o b s e r v e r to view a s u c c e s s i o n o f sm a ll (2 mm.) c i r c l e s a p p e a r i n g on a ground g l a s s s c r e e n and t o re s p o n d by t u r n i n g a c ra n k w henever a s l i g h t l y l a r g e r (3 mm.) c i r c l e a p p e a r e d . In t u r n i n g th e c r a n k th e o b s e r v e r t r i p p e d th e s h u t t e r o f a camera t h a t p h o to g ra p h e d th e c i r c l e , th e r e b y a l l o w i n g th e e x p e r i m e n t e r t o d e te r m in e w h e th e r a s i g n a l a c t u a l l y was p r e s e n t . E i g h t e e n Ss e a c h s e r v e d in two o n e - h o u r s e s s i o n s a t t h i s t a s k , d u r i n g which tim e s i g n a l s o c c u r r e d random ly a t a r a t e o f tw e n ty p e r h o u r . In one s e s s i o n , th e o b se rv e r worked a lo n e In th e e x p e r i m e n t a l room. In th e o t h e r s e s s i o n , th e e x p e r i m e n t e r was p r e s e n t In th e room, b u t o u t o f s i g h t o f th e o b s e r v e r . D uring h i s p r e s e n c e , th e e x p e r i m e n t e r made th e "norm al n o i s e s " a s s o c i a t e d w i t h w o rk in g a t h i s d e s k , b u t d id n o t communicate w i t h th e o b s e r v e r . The r e s u l t s o f F r a s e r ’s s t u d y I n d i c a t e d b e t t e r p e rfo rm a n c e when th e e x p e r i m e n t e r was In th e room. When the e x p e r i m e n t e r was a b s e n t , 89*1^ o f th e s i g n a l s were d e t e c t e d ; when he was p r e s e n t , 95*5^ were d e t e c t e d . T h is was a s t a t l s t i c a l l y s i g n i f i c a n t d i f f e r e n c e (p- . 0 1 ) , b u t f u r t h e r I n s p e c t i o n o f th e d a t a r e v e a l e d t h a t t h e d i f f e r ence was a t t r i b u t a b l e to o n l y se v en Ss. The r e m a in i n g 21 e l e v e n Sa showed no d i f f e r e n o e In p e rfo rm a n c e u n d e r th e two c o n d i t i o n s , F r a s e r * s r e s u l t s a re somewhat d i f f i c u l t to I n t e r p r e t In term s o f th e h y p o t h e s i s o f the p r e s e n t s t u d y . Here th e p ro b lem c o n o e r n s I r r e l e v a n t s e n s o r y s t i m u l a t i o n ; w h e re a s In F r a s e r ’s s t u d y th e p r e s e n c e o f t h e e x p e r i m e n t e r may have been I n t e r p r e t e d by some Ss a s r e f l e c t i n g on t h e i r t r u s t w o r t h l n e s s o r on the e x c e l l e n c e o f t h e i r p e r f o r m a n c e . Thus th e e x p e r i m e n t e r ’s p r e s e n c e may have had m o t i v a t i o n a l p r o p e r t i e s q u i t e I n d e p e n d e n t o f s e n s o r y s t i m u l a t i o n p r o p e r t i e s . CHAPTER IV EXPERIMENT Is EXTRANEOUS AUDITORY STIMULATION AND VISUAL VIGILANCE The p u rp ose o f th e f i r s t e x p e rim e n t was to i n v e s t i g a t e th e e f f e c t s o f e x t r a n e o u s , n o v e l, a u d i t o r y s t i m u l a t i o n on p erform an ce o f a v i s u a l v i g i l a n c e t a s k . The h y p o t h e s i s was t h a t w a t c h s t a n d e r a w i l l d e t e c t a g r e a t e r p e r c e n t a g e o f s i g n a l s on a v i s u a l d i s p l a y when a v a r i e t y o f i r r e l e v a n t a u d i t o r y s i g n a l s a re c o n t i n u o u s l y p r e s e n t e d d u r in g watch th a n when an u n ch ang ing a u d i t o r y s i g n a l i s p r e s e n t e d . Method S u b j e c t s ... The Ss were t w e n t y - e i g h t Navy e n l i s t e d men a s s ig n e d to th e U nited S t a t e s F l e e t A n ti-su b m a rin e W arfare S chool, San Diego. H a lf were r e c e n t g r a d u a t e s o f the ASW School and h e ld sonarmen r a t i n g s . The o t h e r h a l f were a s s ig n e d to " c a s u a l " d u t i e s : mess coo ks, b o a t c o x sw a in s, yeoman, and m ain ten a n ce men. All Ss were a s s ig n e d to the e x p e rim e n t as a p a r t o f t h e i r r e g u l a r d u t i e s . The f o u r t e e n sonarmen had been In the Navy ab ou t 22 23 n i n e months a t th e tim e o f th e e x p e rim e n t, w ere betw een s e v e n te e n and tw enty y e a r s o l d , and had a mean s c o r e c o r r e s p o n d in g to a c e n t l l e r a n k o f 83 on th e G en eral C l a s s l f l o a t i o n T e s t . A ll b u t f o u r w ere h ig h sc h o o l g r a d u a t e s . The f o u r t e e n c a s u a l p e r s o n n e l had b e en i n th e Navy betw een f i v e and e i g h t m onths, ran g ed In age from s e v e n t e e n to t h i r t y - t w o y e a r s (o n ly t h r e e were over tw e n ty y e a r s o l d ) , and had a mean s c o r e c o r r e s p o n d i n g to a c e n t l l e r a n k o f Sh on th e G e n era l C l a s s i f i c a t i o n T e s t . Only two men had com pleted h ig h s c h o o l , b u t a l l had com pleted a t l e a s t th e n i n t h g r a d e . The v i s u a l v i g i l a n c e t a s k . 3s were r e q u i r e d to d e t e c t an I n c r e a s e In th e b r i g h t n e s s o f a l i g h t a p p e a r in g In a o n e - i n c h s q u a r e g r o u n d - g l a s s co v ered a p e r t u r e . The l i g h t was I n t e r m i t t e n t , on f o r one second and o f f f o r two se c o n d s . Upon o b s e r v i n g an i n c r e a s e In b r i g h t n e s s (a s i g n a l ) 3 I n d i c a t e d h i s d e t e c t i o n by p r e s s i n g a h a n d h e ld s w it c h . The type o f s i g n a l to be d e t e c t e d Is I l l u s t r a t e d In F ig u re ? . In d e p e n d e n t v a r i a b l e s . The main in d e p e n d e n t v a r i a b l e was th e c o n d i t i o n of a u d i t o r y s t i m u l a t i o n d u r i n g p erform an ce of th e v i s u a l v i g i l a n c e t a s k . Two c o n d i t i o n s were u s e d : 2k S i g n a l s JUUliUUliUUUUU^^ 2 0 30 ’Co" TIME ON WATCH IN SECONDS F ig u re 2 . Type of s i g n a l used In the experi m en tal t a s k . 25 V a r i e t y . Many d i f f e r e n t k in d s o f a u d i t o r y s i g n a l s were p r e s e n t e d t h r o u g h a s p e a k e r mounted above the v i s u a l d i s p l a y . The modal I n t e n s i t y was 72 db w i t h a 6 I 4 .-SO db r a n g e . C o n t r o l . W hite n o i s e was c o n t i n u o u s l y p r e s e n t e d th r o u g h th e s p e a k e r . The modal I n t e n s i t y was 72 db w i t h a o 9- 7h db r a n g e . The v a r i e t y m a t e r i a l s c o n s i s t e d o f f o u r d i f f e r e n t t y p e s o f a u d i t o r y s t i m u l a t i o n : i n s t r u m e n t a l m u s ic , v ocal m u s ic , au d io p o r t i o n s o f t e l e v i s i o n p ro g ra m s, and m e c h a n ic a l n o i s e s ( t r a f f i c , m a c h in e s , random thu m ping s, e t c e t e r a ) . These m a t e r i a l s were ta p e r e c o r d e d s e p a r a t e l y and th en th e t a p e s were c u t i n t o one, two, t h r e e , and f o u r - m i n u t e s e c t i o n s . The s e c t i o n s were random ly s p l i c e d to y i e l d e i g h t v a r i e t y p ro g ram s, each d i f f e r e n t in c o n t e n t , b u t w i t h e q u a l p r o p o r t i o n s o f th e f o u r ty p e s of m a t e r i a l s . For the c o n t r o l m a t e r i a l s w h ite n o i s e was r e c o r d e d f o r a b o u t t e n s e c o n d s . The tap e was th e n s p l i c e d in a loop so t h a t I t p la y e d c o n t i n u o u s l y . Two o t h e r i n d e p e n d e n t v a r i a b l e s were I n c lu d e d in th e e x p e r i m e n t a l d e s i g n , tim e o f day and w a t c h s t a n d l n g p r a c t i c e . The t i m e - o f - d a y v a r i a b l e was ta k e n as m orning v e r s u s a f t e r n o o n w a tc h e s . The p r a c t i c e v a r i a b l e was ta k e n as th e f i r s t fo u r w a tch e s ( f i r s t two d a y s) v e r s u s th e last, f o u r w a tch e s ( l a s t two d a y s ) . Dependent v a r i a b l e s . The main d e p en d e n t v a r i a b l e 2 6 i n t h i s s t u d y was th e p e r c e n t a g e o f s i g n a l s d e t e c t e d . The e f f e c t o f t h e main in d e p e n d e n t v a r i a b l e on t h e number o f f a l s e d e t e c t i o n s ( r e s p o n d in g when no s i g n a l was p r e s e n t e d ) was a l s o s t u d i e d as a m a t t e r o f s e c o n d a r y i n t e r e s t . E q u ip m en t. The e x p e r i m e n t a l a p p a r a t u s c o n s i s t e d o f t h r e e s e p a r a t e s y s te m s : th e v i s u a l s t i m u l u s p r e s e n t a t i o n sy ste m , th e a u d i t o r y s t i m u l u s p r e s e n t a t i o n s y s te m , and the r e s p o n s e r e c o r d i n g s y s te m . A s c h e m a tic d ia g ra m o f th e e x p e r i m e n t a l a p p a r a t u s l a p r e s e n t e d in F i g u r e 3* The v i s u a l s t i m u l u s was c o n t r o l l e d by two s w i t c h e s . One s w itc h c o n t r o l l e d an o n - o f f r e l a y and was o p e r a t e d by a t h i r d - c u t cam r e v o l v i n g a t a c o n s t a n t speed o f 20 rpm, p r o d u c i n g a l i g h t t h a t was on f o r one second and o f f f o r two s e c o n d s . The o t h e r s w it c h c o n s i s t e d o f a s t y l u s , c o n t a c t p l a t e , and punched 35 mm. t a p e . T h is s w i t c h in t u r n c o n t r o l l e d a r e l a y which v a r i e d the i n t e n s i t y o f th e l i g h t (p rod uced s i g n a l s ) by d i r e c t i n g the c u r r e n t th r o u g h a p p r o p r i a t e r e s i s t a n c e s . T his a rra n g e m e n t a llo w e d s i g n a l s to be programmed b e fo r e h a n d sim p ly by p u n c h in g h o l e s i n t h e 35 mm. t a p e a t a p p r o p r i a t e i n t e r v a l s . The a u d i t o r y s t i m u l i w ere p r e s e n t e d t h r o u g h s p e a k e r s mounted in th e w a t c h s t e n d i n g b o o t h s . A ll s p e a k e r s were c o n n e c te d in p a r a l l e l to th e o u t p u t t e r m in a l s o f a ta p e r e c o r d e r . The S s f r e s p o n s e b u t t o n s , mounted on th e top o f I - © SlIUKt'T'S (oxfcou. t p n m l l r l for r s r h S) 21 H C>H ■ / I > -U - {: > v r \ signs! rtrcuit ■ — — - i . n. i f\ I (II1 .: .(III. | h;irVgrouni) rircull I ! ;w rv r r - *i hcniiT i ire u 11 t M , >* i > I- i I 10 So /X I * ^ 4\p I!" ' 0 X I't- K I M h V fK H ' s ( I IX<M >1J-. A . J h r hox. 1 . t, \{X h - i M x r x . B . S * 9 T * * Ipo r > S ' S w l ! ' h M . 1 J t * t * I n ■ J a ) s f . S * f t ip « * fifc r r S K i I - • r 1 nn'-.im jus ,'t i-« h ,i a n D . S's display J j g P i I pon r^rordrr. (M X ) w . proj^rt ton lam p). 1 . 1 on M rm . K . ! V r s m m . punrhnl In (it 1 ’. \*vn no. 1 * '. ► . Stylus. 1 , I'm no. JU , < •. f ont art pinto. •J . IV n s nos . 1 -1 j t. H . («m -drivon sprocket . u. M otor on-off iMiuh. I . 1 «m -ilriv<’n m jrroswi I i h . . St inu1 u s rountPT. .! . L ' « 5 t p m ronslant sprod y. Display on-off SM ilih, r* nrhrortous tnotor♦ K . h * s display light. K . H iim l— «p rrM t#»il signal s, K '% spanker. inirrt ion si« 11 eh . J. T apr ri'fordnr playback. f i g u r * * ^ h d i a g r a m -it t r *- * ■ x r i me nt a i ♦ p i ^ r ^ i u s , 28 35 wni. f i l m c a s s e t e s * o p e r a t e d s i l e n t l y and w ere c o n n e c te d by a l o n g co rd to a Jack b o x. Thus th e Sa c o uld m o n ito r t h e v i s u a l d i s p l a y w h i l e s e a t e d w i t h the r e s p o n s e b u t t o n s In t h e i r hands* and no movement o t h e r th a n a d e p r e s s i o n o f th e thumb was r e q u i r e d to make a r e s p o n s e . An E s t e r l i n e - Angus r e o o r d e r was u se d to r e c o r d e a c h S*s r e s p o n s e s and th e o n s e t and o f f s e t o f th e b ack g ro u n d and s i g n a l l i g h t s . The e q u ip m en t was I n s t a l l e d i n two rooms a t th e ASW Scho ol ( F i g u r e i | ) . One room c o n t a i n e d e ig h t * sound- c o n t r o l l e d * w a t c h s t a n d l n g b o o th s o f w h ich se v e n w ere used i n t h i s s t u d y . The b o o th s were a p p r o x i m a t e l y 1+f by 8 ' and were a r r a n g e d a lo n g one w a ll o f th e room. Each b o o th was i l l u m i n a t e d by a 1 0 0- w a t t o v e rh e a d lamp and was a i r c o n d i t i o n e d to p r o v i d e a c o n s t a n t wet b u l b t e m p e r a t u r e o f a b o u t 70° F. O u ts id e th e b o o th s was a l a r g e chamber t h a t co u ld be d a rk e n e d i n d e p e n d e n t l y and c o n t a i n e d a s e p a r a t e d i s p l a y f o r a p r o c t o r . One-way windows were i n s t a l l e d on th e d o o rs o f th e b o o th s so t h a t when th e o u t s i d e room was d a rk e n e d and th e b o o th s w ere i l l u m i n a t e d * th e p r o c t o r c o u ld o b s e r v e t h e Ss w i t h o u t d i s t u r b i n g them. T his a rra n g e m e n t was shown to th e Ss. The e x p e r i m e n t e r *s e q u ip m en t was I n s t a l l e d i n a l a r g e room t h a t was c o m p l e t e ly s e p a r a t e d from th e w atch - s t a n d i n g b o o t h s . One s e c t i o n o f t h i s room was u sed as an asse m b ly a r e a f o r th e Ss b e f o r e e a c h w a t c h s t a n d l n g p e r i o d . oq assem b ly a r e a E 's s t a t i o n Watc u n o c cu p ied room ^ s ta n d in g b o o th s n □ p r o c t o r d i s p l a y . m : b ooth #7 Speaker V isu a l d i s p l a y jV P : v P* I i L i F ig u r e i|. one-way m ir r o r Layout o f e x n e r lm e n ta l f a c i l i t i e s * 30 Watch s c h e d u l e . The t w e n t y - e i g h t Ss were d i v i d e d I n t o f o u r 7 -n a n g roups and a s s i g n e d t o w a t c h s t a n d l n g s e s s i o n s a c c o r d i n g t o th e s c h e d u le shown In T able 1. Groups A and B were c a s u a l Navy p e r s o n n e l and Groups C and D were sonarm en. The s c h e d u le shown in T able I i s a c o m p o site o f two r e p l i c a t e d s t u d i e s . D u rin g th e f i r s t week Oroups A and B co m p leted t h e i r w a t c h s t a n d l n g s e s s i o n s , and t h e n th e s tu d y was r e p e a t e d u s i n g Groups C and D. TABLE I SCHEDULE OF WATCHSTANDING SESSIONS Day 1 Day 2 Day 3 Day I 4. V a r . Con. Var. Con. . t , a ) > Con. Var. Con. 8 AM A C B D D B C A 10 A M D B C A A C P D 1 PM C A D B B D A C 3 PM B D A C C A D B Each S s e rv e d in e i g h t w a t c h s t a n d l n g s e s s i o n s , f o u r u n d e r th e v a r i e t y c o n d i t i o n and f o u r u n d e r th e c o n t r o l o o n d i t i o n . S e s s io n s o c c u r r e d In the m orning and a f t e r n o o n e a c h day f o r f o u r d a y s . As I n d i c a t e d in T able I c o n d i t i o n s were c o u n t e r b a l a n c e d so t h a t e f f e c t s a t t r i b u t a b le to a u d i t o r y c o n d i t i o n s , tim e o f d a y , p r a c t i c e , and i n t e r a c t i o n s could be e v a l u a t e d . The bs a l s o were r o t a t e d among the sev en w a tc h s ta n d ln g b o o t h s . S ig n a l I n t e n s i t y . The s i g n a l I n t e n s i t y was s p e c i f i e d as th e b r i g h t n e s s d i f f e r e n c e d ls c r lm ln a b le w ith 90^ a ccu racy by a l e r t e d S s . The p h y s i c a l v a lu e o f t h i s d i f f e r e n c e was e s t a b l i s h e d in a p r e lim in a r y p s y c h o p h y s le a l s tu d y u s in g the 3s who l a t e r took p a r t in the main e x p e r i m ent. The method and r e s u l t s o f t h i s stu d y are d e s c r ib e d in Appendix I. S ig n a l p r e s e n t a t io n s c h e d u l e . P rio r to the exp erim en t fo u r d i f f e r e n t s i g n a l p r e s e n t a t io n s c h e d u le s (Appendix I I ) were programmed on 35 n®». t a n e s . D uring the exp erim en t each tape was p lay ed forward once and backward o n c e , th e re b y p ro d u cin g e i g h t d i f f e r e n t s i g n a l s c h e d u le s , one fo r each w atch . The fo u r ta p e s were programmed to produce 2 1 , 2 3 , 2 5 * and 27 s i g n a l s per hour, r e s u l t i n g In an average s i g n a l r a te o f 2l\. s i g n a l s per hour. Table II shows th e number o f s i g n a l s o c c u r r in g in f i f t e e n - m i n u t e n e r lo d s fo r each o f the s i g n a l p r e s e n t a t io n s c h e d u le s . Taken a c r o s s a l l s c h e d u le s , an average o f s i x s i g n a l s o ccu rred In each f i f t e e n - m i n u t e p e r io d o f w a tc h s ta n d ln g . D i f f e r e n t numbers o f s i g n a l s were p r e se n te d on d i f f e r e n t w atches to p r e v e n t Ss from a c c u r a t e l y p r e d i c t i n g the number o f s i g n a l s to be g iv e n in any watch p e r io d . Each S r e c e iv e d a t o t a l o f 192 s i g n a l s d u rin g the 32 e i g h t w a t c h s t a n d ln g s e s s i o n s . The s i g n a l s c h e d u le s were d i s t r i b u t e d so th a t ea ch S r e c e i v e d 96 s i g n a l s d u rin g e a ch o f the f o l l o w i n g c o m b in a tio n s o f w a tc h s ta n d ln g s e s s i o n s : I 4 . s e s s i o n s under v a r i e t y c o n d i t i o n s , 1 + s e s s i o n s under c o n t r o l c o n d i t i o n s , m orning s e s s i o n s , Ij. a f te r n o o n s e s s i o n s , s e s s i o n s d u rin g th e f i r s t two d a y s, s e s s i o n s d u rin g th e l a s t two d a y s . TABLE II NUMBER OP SIGNALS OCCURRING IN 15-MINUTE INTERVALS O N DIFFERENT SIGNAL PRESENTATION SCHEDULES S i g n a l P r e s e n t a t i o n S c h e d u le T o ta l Mean ( Played 1 2 f o r w a r d ) 3 k ( P lay ed 1 2 b a c k w a r d ) 3 4 1 s t 1^ rain. 5 6 6 5 5 6 7 8 he 6 2nd 15 m in. 5 6 6 7 6 5 6 7 he 6 3rd 15 m in. 6 5 6 7 5 6 6 7 he 6 l±th 15 m in. 5 6 7 8 5 6 6 5 he 6 T o ta l w atch 21 23 25 27 21 23 25 27 192 ?h I n t e r s i g n a l i n t e r v a l s w ere s e l e c t e d u s in g a t a b l e o f random numbers. T h is p ro ced u re had two e f f e c t s : th e s i g n a l s o c cu rr ed randomly in tim e ( t h e r e f o r e presum ably u n p r e d ic t a b le by th e S s ); and the d i s t r i b u t i o n o f i n t e r s i g n a l i n t e r v a l s was r e c t a n g u l a r , as i n d ic a t e d in 33 T ab le I I I . I n t e r v a l s ranged from 12 se c o n d s to 300 s e c o n d s , w it h a mean I n t e r v a l o f llj.6 s e c o n d s . TABLE I I I DISTRIBUTION OF INTERSIGNAL INTERVALS I n t e r s l g n a l I n t e r v a l In Seconds L ess than 60 F re q u e n c y 6o - 119 l? o - 179 180 - 239 39 2^0 - 300 35 P r o c e d u r e . * The day b e f o r e th e e x p e r im e n t began the Ss were a ssem b led and t o l d th e g e n e r a l n a tu r e o f th e e x p e r im e n t. The e x p e rim en t was d e s c r ib e d as "a s t u d y o f th e a b i l i t y o f men to rem ain a l e r t d u rin g a p r o lo n g e d w a tc h ." The s p e c i f i c e x p e r im e n t a l h y p o t h e s is was n o t m en tio n e d . The e x p e r im e n te r and th e n i v a l o f f i c e r In ch arge t o l d th e Ss t h a t t h e i r p a r t i c i p a t i o n was to be c o n s id e r e d a p a r t o f t h e i r r e g u la r d u t i e s , t h a t th e y would be Inform ed o f tho q u a l i t y o f t h e i r perform ance at the end o f th e e x p e rim en t b u t t h a t t h e i r perform ance would n o t a f f e c t t h e i r p e r s o n a l c a r e e r s in th e Navy. D u ring th e The proced u re d e s c r ib e d h ere was r e p e a t e d t w ic e : w it h Groups A and B d u rin g th e f i r s t week and w ith Groups C and D d u rin g th e secon d w eek. p e s t o f th e day th e Ss p a r t i c i p a t e d in th e p r e lim in a r y p s y c h o p h y s ic a l s t u d y (Appendix I ) . On th e aeoond day t h e Ss r e p o r t e d in groups o f s e v e n men a t t h e i r a p p o in te d tim e s (T ab le ! ) • The p r o c e dure was e x p la in e d in th e f o l l o w i n g i n s t r u c t i o n s : T h is i s a stu d y o f human a l e r t n e s s . You w i l l s e r v e as s u b j e c t s in a t o t a l o f e i g h t on e-h ou r w a tc h s ta n d ln g s e s s i o n s , once in th e m orning and once in th e a f t e r n o o n each day f o r the n e x t fo u r d a y s . You have e a ch been g iv e n a s o h e d u le i n d i c a t i n g the tim e you are to a r r i v e h e r e and th e number o f th e b o o th t o w h ich you have been a s s ig n e d f o r e a c h w a tc h . R ep ort f i r s t t o th e a sse m b ly a r e a . Upon i n s t r u c t i o n s from th e p r o c t o r you w i l l p r o ceed to your a s s ig n e d b o o th . You w i l l be g o in g t o a d i f f e r e n t b o o th e v e r y tim e , so be c e r t a i n to ch eck your s c h e d u le c a r e f u l l y f o r your b o o th number. The p r o c to r w i l l make an a d d i t i o n a l ch eck t o make su re each man i s in h i s a s s ig n e d b o o th . Upon e n t e r i n g th e b o o th , c l o s e th e door and s i t in th e c h a ir f a c i n g th e b la c k box mounted on the w a l l . Take th e s m a ll y e llo w s w it c h can from i t s hanger and h o ld i t i n your p r e f e r r e d hand so t h a t you may e a s i l y d e p r e s s th e b u t t o n w it h your thumb. D u ring w a tc h s ta n d ln g a b l i n k i n g l i g h t w i l l appear i n the l i t t l e window o f th e b la c k box. The l i g h t w i l l c o n tin u e to f l a s h a t a c o n s t a n t b r i g h t n e s s l e v e l . Now and th en a f l a s h w i l l be s l i g h t l y b r i g h t e r than u s u a l . These s l i g h t l y b r i g h t e r f l a s h e s w i l l be c a l l e d s i g n a l s . Your Job i s to w atch th e b l i n k i n g l i g h t c o n t i n u o u s l y d u r in g w atch and to r e p o r t t h e s e s i g n a l s by p r e s s i n g th e b u tto n a s q u i c k ly as you can w henever you s e e o n e. T h is i s what th e s i g n a l s w i l l lo o k l i k e . At t h i s p o i n t th e Ss were shown a s e r i e s o f s i g n a l s u n t i l ea oh S was s a t i s f i e d t h a t he u n d e rsto o d what he was to w atch f o r and r e p o r t .J Now you w i l l n o t i c e t h a t th e b oo th a l s o c o n t a in s a sp e a k e r mounted above th e b la c k b o x . W hile you are w a to h ln g th e b l i n k i n g l i g h t f o r th e appearance o f s i g n a l s , you w i l l a l s o h ea r sounds coming from the s p e a k e r . D u ring one o f your w a tc h e s each day you 3 5 w i l l hoar o n ly a oo n tin u ou a n o i s e th a t sounds l i k e s t a t i c . [The w h ite n o la e waa d e m o n s tr a te d .] During the o th e r watoh eaoh day you w i l l hear a v a r i e t y o f aounda: mualc o f v a r io u s k i n d s , p e o p le t a l k i n g , and v a r io u s m eoh a n lca l n o i s e a . [ S e v e r a l p o r t i o n s o f a v a r i e t y program w ere d e m o n s tr a te d .] The sounds you h ea r w i l l have n o th in g t o do w ith the o oou rren ee o f s i g n a l s . No m atter what you hear ov er th e sp e a k e r , your prim ary d u ty la to keep w atch on th e b lin k in g l i g h t and to r e p o r t e v e r y s i g n a l you a e e . Each w a tc h sta n d ln g s e s s i o n w i l l c o n s i s t o f fou r p h a s e s : Warm-up. The f i r s t phase Is a warm-up s e s s i o n l a s t i n g about one m in u te . I t s purpose i s t o r e f r e s h your memory o f what a s i g n a l lo o k s l i k e and does n ot count on th e t o t a l s c o r e . Then the l i g h t w i l l go out f o r 15 se c o n d s . P r e t e s t . When th e l i g h t goes on th e second p h a se , c a l l e d the p r e t e s t , w i l l b e g i n . The p r e t e s t l a s t s two m inu tes and d u rin g t h i s tim e s i g n a l s w i l l occur f r e q u e n t l y . The l i g h t w i l l go o u t ag a in f o r 15 se c o n d s . Main Watch. When the l i g h t goes on the t h ir d p h a se , c a l l e d th e main w a tch , w i l l b e g in . The main watch l a s t s one hour and d u rin g t h i s time s i g n a l s w i l l occur l e s s f r e q u e n t l y than d u rin g the p r e t e s t . The l i g h t w i l l go out aga in f o r 15 seconds a t th e end o f the main w atoh. P o s t t e s t . When th e l i g h t g o e s on th e fo u r t h p h a se , c a l l e d the p o s t t e s t , w i l l b e g in . The p o s t t e s t l a s t s two m in u te s and d u rin g t h i s time s i g n a l s w i l l occu r f r e q u e n t ly as In the p r e t e s t . At th e end o f the p o s t t e s t the l i g h t w i l l go out and th e sound, which w i l l have been on c o n t in u o u s ly throughout a l l fou r p h a s e s , w i l l go o f f . You may th en le a v e th e booth and r e tu r n to your r e g u la r d u t i e s . 36 Whenever you d e t e c t a s i g n a l- - w h e t h e r I t be d u rin g th e warm-up, p r e t e s t , main w a tc h , or p o s t t e s t — p r e s s your r e s p o n s e b u tto n Im m ediately one tim e . I f you do n o t p r e s s th e b u tto n b e f o r e t h e n e x t l i g h t cornea on, I t w i l l be sc o re d a s a m issed s i g n a l . T his means, In o th e r w ord s, th a t you have a maximum o f th r ee secon d s In w hich to r e sp o n d . The rem ainder o f th e I n s t r u c t i o n s d e a l t w ith c e r t a i n r u l e s and o p e r a tin g p r o c e d u r e s . The Ss were t o l d t o keep the door c lo s e d and the overhead l i g h t on, to avoid tam pering w ith the equipment and s i m i l a r r e s t r i c t i o n s . They were p e r m itte d to smoke w h ile on w atoh, b u t were s h a r p ly warned a g a i n s t s l e e p i n g or com m unicating w it h each o th e r In any way d u rin g w a tch . They were shown how the p r o c to r oould u se th e one-way windows to see w hether a man was awake or a s l e e p . A fte r th e Ss had been I n s t r u c t e d in the procedure th e y were g iv e n a b r i e f p e r io d o f p r a c t i c e . Then the e x p e r im e n ta l w a tc h s ta n d ln g s e s s i o n s began. During the warm-tip s e s s i o n s s i g n a l s were p r e se n te d f r e q u e n t l y , on the a v era ge o f th r ee per m in u te . The warm-up was c o n tin u ed u n t i l e a ch 5 had d e t e c t e d a t l e a s t two s i g n a l s , and seldom l a s t e d lo n g e r than a m inute or s o . F iv e s i g n a l s , randomly spaced in tim e , o ccu rred in each o f the tw o-m inute p r e t e s t s and p o s t t e s t s . Two i n v e s t i g a t o r s condu cted th e e x p e r im e n t. One se rv e d as " e x p e r im e n te r ’ 1 and o p e ra ted th e e x p e r im e n ta l a p p a ra tu s. The o th e r se rv e d as " p r o c to r ” and was 3? s t a t i o n e d in the chamber o u t s i d e th e S s ' b o o th s . B efo re ea ch w atch the p r o c to r made su re each S was s t a t i o n e d in h i s a s s ig n e d b o o th and a d j u s t e d the r e s p o n s e s w it c h c o n n e c to r s a t th e Jack box ( s e e F ig u r e 3 ) so t h a t th e r e s p o n s e s o f e a ch S were alw ays r e c o r d e d on th e same ch a n n el o f th e B s t e r l l n e - a n g u s r e c o r d e r r e g a r d l e s s o f w hich b oo th he happened to be a s s ig n e d . P e r i o d i c a l l y d u r in g w a tc h s ta n d ln g th e p r o c to r s i l e n t l y o b serv ed th e Ss through th e one-w ay windows to s e e w hether or n o t the Ss w ere awake (e y e s o p e n ) . When a man was found t o be a s l e e p ( e y e s c lo s e d fo r a t l e a s t f i v e m in u te s) th e p r o c to r e n t e r e d t h i s f a c t in a l o g , but did n ot d i s t u r b the s l e e p i n g S. R e s u l t s The v i g i l a n c e d e c r e m e n t. F igu re 5 shows th e p e r c e n ta g e o f s i g n a l s d e t e c t e d by a l l Ss on a l l w a tc h e s as a f u n c t i o n o f tim e on w a tc h . A r a p id decrem ent in d e t e c t i o n p erform ance o o c u r re d b etw een th e p r e t e s t and the b e g in n in g o f th e w a t c h (shown in F ig u re F as a l i n e o f d a s h e s ) . An a d d i t i o n a l deorem ent took p l a c e w i t h i n the w atch (shown as a s o l i d l i n e ) ; th e decrem ent occu rred w i t h i n th e f i r s t h a l f hour o f w atch w it h perform ance rem a in in g s t a b l e a t a red u ced l e v e l t h e r e a f t e r . On the p o s t t e s t , perform ance r e tu r n e d a b r u p tly and c o m p le t e ly to PERCENTAGE 0 ? VISUAL SIGNALS DETECTED 100, 90 3* 80 \ 7 0 - 6oU 80 \ \ Uo1 1 0 Pre t e s t 1 IS 30 MINUTES OF WATCH . L . J 6o Post t o s t F igu re 5* P ercen tage o f s i g n a l s d e t e c t e d on a v i s u a l v i g i l a n c e t a s k as a f u n c t io n o f time on watch (N * 2 8 ). 39 th e I n i t i a l p r e t e a t l e v e l . E f f e c t o f i r r e l e v a n t a u d it o r y s t i m u l a t i o n . The e f f e c t o f th e main In depend en t v a r ia b le i s shown in F ig u re 6 . Perform ance during th e p r e t e s t and d u rin g the f i r s t f i f t e e n m in u te s o f w atch was the same under c o n d i t i o n s o f v a r i e t y a u d it o r y s t i m u l a t i o n and under the w h ite n o i s e c o n d i t i o n s . Perform ance under v a r i e t y audio c o n d i t i o n s c o n tin u ed to d e o l in e d u rin g th e second f i f t e e n m inutes* bu t th en showed a trend toward r e c o v e r y d u rin g th e l a s t h a l f hour o f w atch . Performance under w h ite n o i s e d e c lin e d c o n t in u o u s ly throughout the w atch. On the p o s t t e s t perform ance r e c o v e r e d c o m p le te ly fo r both c o n d i t i o n s . During th e f i r s t f i f t e e n m in u tes o f watch somewhat more f a l s e d e t e c t i o n s were r e p o r te d under v a r i e t y audio c o n d i t i o n s than under w h ite n o i s e c o n d i t i o n s . During the rem ainder o f watoh th e r e was no d i f f e r e n c e in f a l s e d e t e c t i o n s betw een th e s e c o n d i t i o n s (F ig u re 7 ) . E f f e c t s o f p r a c t i c e . D e t e c t io n perform ance improved e a ch day under a l l c o n d i t i o n s o f w a to h ste n d in g . The p e r c e n ta g e o f s i g n a l s d e t e c t e d in c r e a s e d e a ch day (F ig u re 8) and the number o f f a l s e d e t e c t i o n s d ecrea sed ( F ig u re 9 ) . E f f e o t s o f time o f d a y . There ap p ea re d to be C E N T VISUAL SIGNALS DETECTED hO 1 0 0 90 e o H O 70 6oh arif't-v auO't' C L , 50 ]|0 i 0 Pre t e s t i 1 15 30 MINUTES OF W ATCH i. 6o Poa t teat F igu re 6. P ercen ta g e o f s i g n a l s d e t e c t e d on a v i s u a l v i g i l a n c e ta s k as a f u n c t io n o f time on watch fo r two c o n d it io n s o f i r r e l e v a n t a u d ito r y s t i m u l a t i o n (N = , M E A N N U M B E R FALSE DETECTIONS 1+1 1 0 i 9- 6 * 5* \ \ sV a r le ty Audio \ Whit© ii_ No la© 3' ?i 1 1 I I i J 0 10 30 60 minutes of watch F igu re 7. Mean number o f f a l s e d e t e c t i o n s on a v i s u a l v i g i l a n c e ta s k as a fu n c tio n o f time on watch under two c o n d i t i o n s o f e x tr a n e o u s a u d ito r y s t i m u l a t i o n (N = ?H). PERCENTAGE O P SIGNALS k? 1 9 5 - 70 . o 6o STTCCESSIVE DAYS OP ’VAT0H3TAND[ NG F ig u r e 8 . P e r c e n ta g e o f s i g n a l s d e t e c t e d on a v i s u a l v i g i l a n c e t a s k on s u c c e s s i v e days o f w a tc h s te n d in g (N s 2 8 ). N U M B E R O F FALSE DETECTIONS 30- 20 ' - 93 b- 10[ O' A 1 1 -------- 1 ---- 1 2 3 k SUCCESSIVE DAYS OF WATCHSTANDINti F ig u re 9« Mean number o f f a l s e d e t e c t i o n s r e p o r te d on s u c c e s s i v e days o f v i s u a l w atch- sta n d in g {N = 2 8 ) . kk l i t t l e d i f f e r e n c e betw een d e t e c t i o n perform ance on morning and a f t e r n o o n w a tc h e s when a l l d ata were com bined. On a l l m orning w a to h es 6i ^ o f th e s i g n a l s were d e t e c t e d ; on a l l a f t e r n o o n w a tc h e s 6 3 % were d e t e c t e d . Sonarmen v e r s u s c a s u a l p e r s o n n e l . The d e t e c t i o n perform ance o f ASW S c h o o l g r a d u a te s was m arkedly s u p e r io r to t h a t o f c a s u a l n a v a l p e r so n n e l (F ig u r e 1 0 ) . P r e t e s t perform ance was n e a r ly e q u a l, but c a s u a l p e r so n n e l s u f f e r e d a more s e v e r e perform ance decrem ent d u rin g w atch than sonarm en, and d id n o t r e c o v e r as w e ll on th e p o s t t e s t . S t a t i s t i c a l s i g n i f i c a n c e o f f i n d i n g s . L i n d q u i s t ' s (1 9 5 6 , page ? 3 7 ) tr e a tm e n ts X tr e a tm e n ts X s u b j e c t s a n a l y s i s o f v a r ia n c e model was used to t e s t th e main h y p o t h e s i s t h a t perform ance on th e v i s u a l v i g i l a n c e ta sk would be b e t t e r under v a r i e t y au d io c o n d i t i o n s than under o o n tr o l (w h ite n o i s e ) c o n d i t i o n s . In a d d i t i o n , the a n a l y s i s was perform ed to t e s t the s i g n i f i c a n c e o f the p r a c t i c e e f f e c t and to t e s t a p o s s i b l e I n t e r a c t i o n between a u d it o r y c o n d i t i o n s and p r a c t i c e . The main e f f e c t s t h a t were t e s t e d in th e a n a l y s i s o f v a r ia n c e are shown in term s o f o v e r - a l l mean p e r c e n ta g e d e t e c t i o n s c o r e s In T able IV. The m o r n ln g -a fte r n o o n d im en sio n was c o ll a p s e d for PERCENTAGE O P VISUAL SIGNALS DETECTED 15 1 0 0 90 o BO 70 Sonar s c h o o l bO Casual Navy p e r so n n e l (N = !.'.) BO ‘*0 - 0- Pre t e s t 1 ............. .........L - ............. 15 30 MINUTES OF WATCH I ; V ' 6o P o s t t e s t F igu re 10. P ercen ta g e o f s i g n a l s d e t e c t e d on a v i s u a l v i g i l a n c e ta sk by li| so n a r men and ll|. c a s u a l p e r so n n e l as a f u n c t i o n o f time on w atch. 16 TABLE IV MEAN PERCENTAGE OF SIGNALS DETECTED AS A FUNCTION OF AUDITORY CONDITIONS AND PRACTICE A u d ito ry C o n d itio n s T o ta l V a r ie ty C on trol F i r s t ? days 6 1 .0 5 6 .7 5 8 .9 Second ? days 7 0 .3 6 6 . k 6 8 . I * . T o ta l 6 5 .7 6 1 .6 6 3.6 t h i s a n a l y s i s fo r s e v e r a l r e a s o n s . This d im en sio n was In trod uced in t o the e x p e r im e n ta l d e s ig n m a in ly fo r c o n tr o l p u rp o ses so th a t the e f f e c t s o f a u d it o r y c o n d i t i o n s and p r a c t i c e cou ld be a s s e s s e d u n e q u iv o c a lly * By com bining th e m orning and a fte r n o o n s e s s i o n s a d d i t i o n a l s t a b i l i t y o f th e resp o n se m easures was o b ta in e d s i n c e t h e s e m easures were th en based on two w atch es in s t e a d o f o n e. T his a l s o s i m p l i f i e d the problem o f what to do about m is s in g so o r e s in the a n a l y s i s o f v a r ia n c e t a b l e . S ix o f th e Ss m issed one w atch each (th e y se rv e d In sev en in s t e a d o f eight- w a t c h e s ) . T h er efo r e s i x o f the 112 e n t r i e s In the a n a l y s i s o f v a r ia n c e t a b le were based on one watch In ste a d o f tw o. T his p roced u re seemed J u s t i f i a b l e on th e grounds th a t th e d a ta showed l i t t l e (ab ou t one per c e n t ) d i f f e r ence betw een perform ance on m orning and a fte r n o o n w atch es and perform ances on t h e s e two o c c a s i o n s were h i g h ly c o r r e l a t e d (r • . l b ) . The r e s u l t s o f th e a n a l y s i s o f v a r ia n c e are shown In T able V. The Improvement In perform ance under v a r i e t y c o n d i t i o n s was v e r y s i g n i f i c a n t ; th u s th e main h y p o t h e s i s was upheld* The Improvement In perform ance as a f u n c t io n o f p r a c t i c e was a l s o v e r y s i g n i f i c a n t . There was no s i g n i f i c a n t I n t e r a c t i o n b etw een a u d ito r y c o n d i t i o n s and p r a c t i c e ; th a t I s , th e s u p e r io r perform ance under v a r i e t y c o n d i t i o n s was m a in ta in e d even a f t e r c o n s i d e r a b l e p r a c t i c e on th e t a s k . TABLE V ANALYSIS OP VARIANCE OP PERFORMANCE ON THE VISUAL VIGILANCE TASK Source d f Mean Square F A. A u d itory ( v a r i e t y o o n d lt io n v s . c o n t r o l ) 1 1 M 2 9 .0 * B. P ra et i ce ( f i r s t ? days v s. second ? days) 1 2 .5 0 8 11. 5* c . Sub j e c t s 21 1 * 185 A X B 1 1 • • • A X C 21 16 B X C 21 219 R e s id u a l (A X E X C) 21 156 ♦ S i g n i f i c a n t beyond the . 0 0 1 l e v e l . CHAPTER V EXPERIMENT I I : EXTRANEOUS VISUAL STIMULATION AND AUDITORY VIGILANCE The r e s u l t s o f th e f i r s t e x p e rim en t v e r i f i e d th e h y p o t h e s is t h a t an I n c r e a s e In th e t o t a l v a r i a b i l i t y o f e n v iro n m en ta l s t i m u l a t i o n would improve v i g i l a n c e p erfo rm a n ce. In th a t e x p e rim en t th e ta sk s t i m u l i were p r e s e n te d on th e v i s u a l mode and the i r r e l e v a n t s t i m u l i were p r e s e n te d on th e a u d it o r y mode. Experim ent II wan th e complement o f Experim ent I; i t s pu rp ose was to t e s t th e same h y p o t h e s i s w ith the stlm u l1 -m o d e r e l a t i o n s h i p s r e v e r s e d . The h y p o t h e s i s t e s t e d In th e second e x p e rim en t was th a t w a tc h s te n d e r s w i l l d e t e c t a g r e a t e r p e r c e n ta g e o f s i g n a l s on an a u d it o r y d i s p l a y when a so u rce o f I r r e l e v a n t , n o v e l , v i s u a l s t i m u l a t i o n I s p r e s e n t In th e environ m en t than when su ch a so u rc e Is n o t p r e s e n t . M e thod S u b j e c t s . The Ss were e i g h t e e n r e c e n t g r a d u a te s o f th e F l e e t ASW S c h o o l, San D ie g o . These men a l l h e ld sonarman r a t i n g s and were s i m i l a r In a g e , g e n e r a l I n t e l l i g e n c e , and e d u c a tio n to the f o u r t e e n sonarmen who lift p a r t i c i p a t e d In th e f i r s t e x p e r im e n t. 1*9 The a u d it o r y v i g i l a n c e t a s k . 3s were r e q u ir e d to d e t e c t an i n c r e a s e in th e lo u d n e s s o f a 750 cps pure ton e d e l i v e r e d through PDR-8 h ea d p h o n es. The t o n e , l i k e the l i g h t in th e v i s u a l v i g i l a n c e t a s k , was i n t e r m i t t e n t — on f o r one secon d and o f f fo r two s e c o n d s . Upon h e a r in g an i n c r e a s e in lo u d n e s s (a s i g n a l ) 3 p r e s s e d a h a n d -h eld r e s p o n s e s w itc h to i n d i c a t e h i s d e t e c t i o n . In d ep en d en t v a r i a b l e s . The main in d ep en d en t v a r i a b l e was th e p r e se n c e or a b sen ce o f a so u r c e o f e x tr a n e o u s , n o v e l , v i s u a l s t i m u l a t i o n in th e w a tc h s ta n d ln g e n v iro n m en t. Ss sto o d w atch under two c o n d i t i o n s : Vgurlety. Each 3 was g iv e n a l a r g e album o f p r i z e - w in n in g p h otog ra p h s and was inform ed t h a t he was f r e e to lo o k th rou gh the album w h ile he m on itored th e a u d it o r y d i s p l a y . Each album c o n ta in e d from 1*00 to 500 p ages o f p h oto g ra p h s o f many s u b j e c t s : la n d s c a p e s , p o r t r a i t s , n u d e s, candid s h o t s , e t c e t e r a . O ther than th e t i t l e s o f t h e p h o to g ra p h s, th e albums c o n ta in e d no w r i t t e n m a t e r i a l . Each 3 was g iv e n a d i f f e r e n t album d u rin g each w atch under t h e v a r i e t y c o n d i t i o n . C o n t r o l. Ss s to o d watch w it h o u t th e album s. A ll o t h e r a s p e c t s o f th e en viron m en t and th e ta sk were the same as i n th e v a r i e t y c o n d i t i o n . Two o th e r in d ep en d e n t v a r i a b l e s were in c lu d e d in the d e sit^ i, time o f day and w a tc h s ta n d ln g p r a c t i c e . The t l m e - o f - d a y v a r i a b l e was taken as m orning v e r s u s a fte r n o o n w a t c h e s . The p r a c t i c e v a r i a b l e was taken as the f i r s t d a y 's w a tch es v e r s u s the secon d d a y ’s w a tc h e s. 50 D ependent v a r i a b l e s . The major dependent v a r i a b l e was th e p e r c e n ta g e o f a u d it o r y s i g n a l s d e t e c t e d . The e f f e c t o f th e main In d ep en d en t v a r ia b le on th e I n c id e n c e o f f a l s e d e t e c t i o n s was a l s o o b s e r v e d , but no h y p o t h e s is c o n c e r n in g t h i s e f f e c t was s t a t e d . Sq ulp m en t. The same a p p a ra tu s used in Experim ent I (F ig u r e 3 ) wa3 used In Experim ent II e x c e p t t h a t the sp ea k er c i r c u i t was e lim in a t e d and in the p la c e o f th e l i g h t d i s p l a y , headphones were i n s t a l l e d . A 750 cps pure ton e was g e n e r a te d by a H e a th k it au d io g e n e r a t o r , a m p li f i e d , and th e n c e p assed through a p p r o p r ia te r e s i s t a n c e s to n in e s e t a o f im pedance-m atched h ead p h on es. The s w it c h i n g c i r c u i t s d e s c r ib e d e a r l i e r (page 27) produced an I n t e r m i t t e n t tone o f c o n s t a n t i n t e n s i t y w ith s l i g h t l y lo u d e r to n e s ( s i g n a l s ) a p p ea r in g a t random I n t e r v a l s . The equipm ent was i n s t a l l e d in a group sonar o p e r a to r t r a i n e r a t th e ASW S c h o o l. The group t r a i n e r c o n ta in e d t e n , s o u n d - c o n t r o l l e d , v e n t i l a t e d b o o th s , o f w hich n in e were used in th e p r e s e n t s t u d y . The booth s were 8 r by 1 0 1 In s i z e and were arranged a lo n g b oth s i d e s o f a c e n t r a l c o r r id o r (F ig u r e 1 1 ) . Each b oo th was I llu m in a te d by a 1 0 0 -w a tt overh ead lamp and c o n ta in e d I n a c t i v e sonar eq u ip m en t. The e x p e r im e n ta l ap p aratu s was I n s t a l l e d in a la r g e chamber a d ja c e n t to th e w a tc h s ta n d ln g b o o th s . Equipment n o i s e s were masked by a v e n t i l a t i o n 51 #1+ #3 H i o »H #5 #6 T R' L #? #7 #1 not used E 's s t a t i o n r~ t F ig u re 1 ) . Layout o f « a tch a ta n d in K b o o th s , E xperim ent I I . 5 2 fan d u r i n g w a t o h s t a n d l n g . T his In a d d i t i o n to the a c o u s t i c a l t r e a t m e n t o f th e b o o th w a l l s p r e v e n t e d sounds from th e e x p e r i m e n t a l a p p a r a t u s from r e a c h i n g t h e 3s d u r i n g w a t c h s t a n d l n g . Watch s c h e d u l e . The e i g h t e e n Ss were d iv id e d ran d o m ly I n t o two groups o f n i n e men. The Ss i n each group sto o d w atch s i m u l t a n e o u s l y In s e p a r a t e w a t c h s t a n d l n g b o o th s a c c o r d i n g to th e sc h e d u le shown In T able VI. Each S s e r v e d in f o u r o n e -h o u r w a t c h s t a n d l n g s e s s i o n s , two w i t h th e albums ( v a r i e t y ) and two w i t h o u t the albums ( c o n t r o l ) . S e s s io n s o c c u r r e d in the m orning and a f t e r n o o n on each o f two c o n s e c u t i v e d a y s . The o r d e r o f e x p e r i m e n t a l c o n d i t i o n s was c o u n te r b a l a n c e d a c r o s s g ro u p s. TABLE VI SCHEDULE OF EXPERIMENTAL CONDITIONS Group A (N - 9 ) Group B (N « 9) Day 1 Day 2 Day 1 Day ? A.M. V a r i e t y C o n tro l C o n tro l V a r ie t y P.M. C o n tro l V a r ie t y V a r i e t y C o n tro l S i g n a l I n t e n s i t y . The s i g n a l I n t e n s i t y was s p e c i f i e d as the l o u d n e s s d i f f e r e n c e d i s c r i m i n a b l e w ith 90^ a c c u r a c y by a l e r t e d Ss. T h is i n t e n s i t y was e s t a b l i s h e d in a p r e l i m i n a r y p s y c h o p h y s ic a l s t u d y d e s c r i b e d In 53 Appendix I. S i g n a l p r e s e n t a t i o n s c h e d u l e . S i g n a l s o o c u rr e d a t random I n t e r v a l s d u r i n g w a t c h s t a n d l n g and were programmed b e f o r e h a n d on punched 35 t®0* ta p e s * D uring e a c h w a tch t w e n t y - f o u r s i g n a l s a p p e a re d , s i x d u r i n g e a c h 1 5-m in u te p e r i o d . A d i f f e r e n t s i g n a l p r e s e n t a t i o n s c h e d u le (se e Appendix I I ) was u se d on e a c h o f th e f o u r w a t c h s t e n d i n g s e s s i o n s . P r o c e d u r e . The p r o c e d u r e was th e sane as t h a t used In E xperim ent I (page 33 )» e x c e p t t h a t Ss s to o d w atch f o r two days I n s t e a d o f f o u r d a y s. Each s e s s i o n c o n ta in e d a warm-up, p r e t e s t , main w a tc h , and p o s t t e s t , J u s t as b e f o r e . Reaults The v i g i l a n c e d e c r e m e n t . The d e t e c t i o n p e r f o r m ance o f a l l Ss u n d e r a l l c o n d i t i o n s i s shown In F ig u re IP as a f u n c t i o n o f tim e on w a tc h . T here was a r a p i d d e c l i n e In p e rfo rm an c e from th e p r e t e s t l e v e l to the b e g in n i n g o f th e w a tc h . A l t h i n th e main watch p e rfo rm a n c e d e c l i n e d l i n e a r l y d u r i n g the f i r s t f o r t y m in u te s and th e n s t a b i l i z e d a t a re d u c e d l e v e l . On t h e p o s t t e s t p e rfo rm a n c e r e c o v e r e d Im m e d ia te ly . E f f e c t o f i r r e l e v a n t v i s u a l s t i m u l a t i o n . The PERCENTAGE O F AT TDITuR'i SIGNALS DETECTED 100 r 90h roL-^ \ \ ? I I \ ! 7 0 - \ / 60 x ■ Q X I I I 5or ° ^ 0 10 20 30 1*0 50 do pp p POST t f s t VINFT F-S of watch t e s t F ig u re 17, P e rc e n ta g e o f a t g n a l e d e t e c t e d on an a u d i t o r y v i g i l a n c e ta s k as a f u n c t i o n o f tim e on watch (N = lR). 5 5 e f f e c t o f the main in d e p e n d e n t v a r i a b l e is shown in F ig u r e 13. Perform ance d u r in g th e p r e t e s t was abo ut th e same w i t h th e albums and w i t h o u t th e albums. Perform ance u nder v a r i e t y c o n d i t i o n s was s u p e r i o r to p erfo rm an ce tinder c o n t r o l c o n d i t i o n s d u r i n g a l l p a r t s o f th e main w a tc h , b u t the v i g i l a n c e decrem ent a o p e a re d u n d e r b o t h c o n d i t i o n s . The v a r i e t y s t i m u l a t i o n seemed to be e s p e c i a l l y e f f e c t i v e d u r i n g th e f i r s t f i f t e e n m in u te s o f w atch. On t h e p o s t - t e s t pe rfo rm an c e r e c o v e re d c o m p le te ly f o r b o th c o n d i t i o n s . There was a ten d e n cy f o r the Ss to make more f a l s e d e t e c t i o n s u nd er v a r i e t y c o n d i t i o n s than under c o n t r o l c o n d i t i o n s . The te n d e n c y was a s l i g h t one and appeared m ain ly a t th e b e g in n in g o f th e w atch (F ig u re llj). E f f e c t s o f p r a c t i c e . D e t e c t i o n p erfo rm an ce Improved as a f u n c t i o n o f p r a c t i c e . On the f i r s t day 5 1. 8# o f th e s i g n a l s were d e t e c t e d ; on th e second day 59.8# o f th e s i g n a l s were d e t e c t e d . The mean number of f a l s e d e t e c t i o n s p er w atch d e c l i n e d from ll+.? on th e f i r s t day to 6 . 1 * on th e second day. E f f e c t s o f tim e o f d a y . There appeared to be l i t t l e d i f f e r e n c e between d e t e c t i o n p erform an ce on m orning and a f t e r n o o n w a tc h e s. On th e m orning w a tc h e s 57# o f the s i g n a l s were d e t e c t e d ; on the a f t e r n o o n w atches 5 5^ were d e t e c t e d . PERCENTAGE O P AUDITORY SIGNALS DETECTED 86 lOOr 90r 80 o r 70 60 \ s^With albums ( V a r ie t y ) \ \ \ V 50 ” ± ko Pre t e a t W ithout albums ( C o n t r o l ) .1 . i 15 30 MINUTES OP WATCH . . . L . bS 6 0 Post t e s t F ig u r e 1 3. P e r c e n ta g e o f s i g n a l s d e t e c t e d on an a u d i t o r y v i g i l a n c e ta s k as a f u n c t i o n o f tim e on w atch u n d e r two c o n d i t i o n s o f v i s u a l s t i m u l a t i o n (N = 1 8 ). M E A N N U M B ® O F FALSE DETECTIONS J7 5 h - \ \ \ V a r i e t y \ C o n tro l ■ O k l b 0L- 0 i. 10 _ L h'S 6o MINUTES OF -.VATCH F ig u re li|. Mean number o f f a l s e d e t e c t i o n s on an a u d i t o r y v i g i l a n c e t a s k as a f u n c t i o n o f tim e on w atch u n d e r two c o n d i t i o n s of v i s u a l s t i m u l a t i o n (N * 1^). 58 S t a t i s t i c a l s i g n i f i c a n c e o f f i n d i n g s . A n a l y s i s o f v a r i a n c e was u se d to t e s t t h e h y p o t h e s i s t h a t p e r fo r m a n c e on t h e a u d i t o r y v i g i l a n c e t a s k w ould be b e t t e r u n d er v a r i e t y ( w i t h a lb u m s) c o n d i t i o n s th a n u n d er c o n t r o l ( w i t h o u t alb u m s) c o n d i t i o n s * The e f f e c t o f p r a c t i c e and p o s s i b l e I n t e r a c t i o n b e tw e e n v i s u a l c o n d i t i o n s and p r a c t i c e w ere a l s o t e s t e d f o r s t a t i s t i c a l s i g n i f i c a n c e . D ata from m o rn in g and a f t e r n o o n w a t c h e s w ere com bined a s In t h e a n a l y s i s o f th e r e s u l t s o f t h e f i r s t e x p e r i m e n t . The m ain e f f e c t s a r e shown i n term s o f mean p e r c e n t a g e d e t e c t i o n s c o r e s In T a b le V II. TABLE VII MEAN PERCENTAGE OP SIONALS DETECTED AS A FUNCTION OP VISUAL CONDITIONS AND PRACTICE V i s u a l C o n d i t i o n s T o t a l V a r i e t y C o n tr o l F i r s t day 5 h . ? <r • Second day 6 7 . 6 51*9 5 9 . 8 T o t a l 6 0 . 9 5 0 . 6 r ; r . 8 The r e s u l t s o f t h e a n a l y s i s o f v a r i a n c e a r e shown in T a b le V I I I . The Im provem ent In p e r fo r m a n c e under v a r i e t y c o n d i t i o n s was s t a t i s t i c a l l y s i g n i f i c a n t , u p h o ld in g th e m ain h y p o t h e s i s . The Im provem ent In p e r fo r m a n c e as a f u n c t i o n o f p r a c t i c e was a l s o s t a t i s t i c a l l y 5 9 s i g n i f i c a n t . T h ere was no s i g n i f i c a n t i n t e r a c t i o n b e tw e e n v i s u a l c o n d i t i o n s and p r a c t i c e . TABLE V I I I ANALYSIS OF VARIANCE OP AUDITORY WATCHSTANDING PERFORMANCE S o u r c e d f Mean S q u are F A. V i s u a l c o n d i t i o n 1 10 1.0 7 .3 ? * B. Days I 7 8 .0 8.0i4* C. B etw een Ss 17 57.1* A X B 1 2 3 .0 s e e A X C 17 13-8 B X C 17 9 .7 R e s i d u a l (A X B X C) 17 1 1 .8 ♦ S i g n i f i c a n t b eyon d th e .0 ? 5 l e v e l . CHAPTER VI DISCUSSION The r e s u l t s o f b o t h e x p e r i m e n t s i n d i c a t e d t h a t an i n c r e a s e i n th e t o t a l v a r i a b i l i t y o f th e w a t c h s t a n d l n g e n v iro n m e n t had a f a c i l i t a t i n g e f f e c t on v i g i l a n c e p e rf o r m a n c e . These r e s u l t s were ta k e n as o o u n t e r e v id e n c e f o r a f i l t e r t h e o r y o f v i g i l a n c e and as s u p p o r t f o r an a r o u s a l t h e o r y o f v i g i l a n c e . I m p l i c a t i o n s f o r t h e F i l t e r T heory The p r e d i c t i o n from th e f i l t e r th e o r y t h a t p e rfo rm a n c e would be a d v e r s e l y a f f e c t e d by com peting s t i m u l i was deduced by th e p r e s e n t w r i t e r from th e p u b l i s h e d s t a t e m e n t s o f B ro a d b e n t (1953*» 1953b, 1957, 1959)* However, i n a r e c e n t p e r s o n a l com m unication B ro a d b en t p o i n te d o u t c e r t a i n f e a t u r e s o f the v i g i l a n c e t a s k s u sed i n t h i s s t u d y t h a t would r e d u c e any d i s t r a c t i n g e f f e c t s o f th e co m peting s t i m u l i . The tim e I n t e r v a l o f two se c o n d s f o r the '’o f f p h a se " o f th e t a s k s t i m u l i was c o n s i d e r e d by B ro a d b en t t o be s u f f i c i e n t l y lo n g f o r any d i v e r s i o n o f t h e f i l t e r to tak e p l a c e s a f e l y w i t h o u t e f f e c t on p e rf o r m a n c e . I t was a l s o c o n s i d e r e d p o s s i b l e 60 th a t ev en I f th e ob aerver were d i s t r a c t e d a t th e a c tu a l tim e o f a r r i v a l o f a s tim u lu s he could r e v e r t to th e main chan n el w i t h i n the o n e -se c o n d "on p h a s e .” Thla would be p a r t i c u l a r l y p o s s i b l e on th e a u d ito r y ta sk (Experim ent I I ) b e c a u se th e o c c u r r e n c e o f th e d i s t r a c t i n g v i s u a l s t im u la t i o n was In t h a t c a se under the S ’ s d i r e c t c o n t r o l , and th e t a s k s t i m u l i would n o t have been sh u t ou t from th e se n s e organs w h ile h i s a t t e n t i o n was d i v e r t e d . Thus the l i s t e n e r would have been a b le t o lo ok a t p a r t i c u l a r l y i n t e r e s t i n g p i c t u r e s d e l i b e r a t e l y d u rin g the tw o-seocn d pau ses betw een t a s k s t i m u l i , and I f he had been lo o k in g at som ething when the a u d ito r y s i g n a l occu rred he would n e v e r t h e l e s s r e o e iv e I t a t h i s se n s e organs and p o s s i b l y d e t e c t I t from memory. Other c h a r a c t e r i s t i c s o f th e e x p e r im e n ta l s i t u a t i o n th a t Broadbent thou ght would d im in is h th e r o l e o f the f i l t e r In t h i s stu d y were the n e a r - t h r e s h o ld i n t e n s i t y o f the s i g n a l s and the r e l a t i v e l y low i n t e n s i t y (72 db) o f the v a r i e t y audio s t i m u l a t i o n . He e v i d e n t l y f e l t th a t the f i l t e r th e o ry may be more a p p r o p r ia t e ly a p p lie d to v i g i la n c e ta s k s w i t h more e a s i l y d e t e c t a b l e s i g n a l s . F u r th e r, u n l e s s th e a u d ito r y m a t e r ia l were o f v e ry g r e a t I n t e r e s t , Broadbent would not e x p e c t I t to have a very d e l e t e r i o u s e f f e c t In the r e g io n o f 72 db. Thus, to g i v e the f i l t e r th e o r y a r e a s o n a b le t e s t , Broadbent f e l t th a t task s t i m u l i o f v ery b r i e f d u r a tio n 6? (a b o u t a q u a r t e r - s e c o n d ) sh o u ld be u sed and t h e s e s h o u ld o c c u r In r a p id s u c c e s s i o n ( a t a b o u t o n e - s e c o n d I n t e r v a l s ) . The s i g n a l l e v e l s h o u ld be w e l l above t h r e s h o l d and th e c o m p e tin g s t i m u l a t i o n sh o u ld be f a i r l y I n t e n s e . W hether or n o t an added d ecrem en t w ould appear u n d er th e e x p e r im e n ta l c o n d i t i o n s s p e o l f i e d In th e p r e c e d in g p a ra g ra p h i s a m a tte r t o be d e c id e d by f u t u r e r e s e a r c h . The f a c t r e m a in s , th o u g h , t h a t th e p r e s e n t e x p e r im e n t a l r e s u l t s c a n n o t be a c c o u n te d f o r in term s o f the f i l t e r t h e o r y . That i s , th e p r e d i c t i o n from th e f i l t e r t h e o r y w ould be e i t h e r t h a t p erfo rm a n ce under v a r i e t y c o n d i t i o n s w ould be p o o r e r th an p erfo rm a n ce under c o n t r o l c o n d i t i o n s or t h a t t h e r e w ould bo no d i f f e r e n c e . The p r e d i c t i o n o f im proved p erfo rm a n ce under v a r i e t y c o n d i t i o n s c a n n o t be made from th e f i l t e r t h e o r y r e g a r d l e s s o f m a n ip u la t io n s o f l n t e r s t l m u l u s i n t e r v a l d u r a t i o n , s t i m u lu s d u r a t i o n , or s i g n a l i n t e n s i t y . F u r th e r m o r e , if the Ss In th e p r e s e n t e x p e r im e n ts w ere c h a n n e l l i n g th e f i l t e r d e v i a t i o n s i n t o t h e i n t e r s t im u lu s p e r i o d , as b ro a d b en t s u g g e s t e d th ey m ig h t h a v e , why was t h e r e a d ec r e m e n t in p erfo rm a n ce as a f u n c t i o n o f tim e on w atch? The o b s e r v e d d ecrem en t m ig h t be a c c o u n te d f o r in term s o f th e f i l t e r t h e o r y , b u t to do so would assume t h a t th e Ss were t a k i n g in i r r e l e v a n t in fo r m a t io n w it h g r e a t e r fr e q u e n c y as t h e w a tc h e s p r o g r e s s e d . I f t h i s 63 assu m p tion v e r s made, and th u s th e decrem ent a ccou n ted f o r , then i t would f o llo w th a t the Ss were n o t s u c c e s s f u l in d i v e r t i n g th e f i l t e r d u r in g th e " s a f e ” p e r io d . To a ccou n t f o r th e d i f f e r e n t i a l perform ance under v a r i e t y and c o n t r o l c o n d i t i o n s , i t would have to be assumed th a t Ss were even l e s s s u c c e s s f u l under c o n t r o l c o n d i t i o n s , an assu m p tion t h a t Is d i a m e t r i c a l l y opposed to th e p r i n c i p l e s o f th e f i l t e r th e o r y . I m p li c a t io n s f o r the A rou sal Theory An o v e r - a l l Improvement in perform ance under v a r i e t y c o n d i t i o n s was p r e d ic t e d from the a r o u s a l th e o ry and t h i s p r e d i c t i o n was v e r i f i e d by th e r e s u l t s o f both e x p e r im e n ts . Thus the a r o u sa l th e o r y was su pp orted by the prim ary e x p e r im e n ta l r e s u l t s . A d d it io n a l su p p o rt may be i n d ic a t e d by th e f a c t th a t in the f i r s t e x p e r im e n t, the e x tr a n e o u s s t i m u l a t i o n had i t s g r e a t e s t e f f e c t d u rin g the l a t e r p e r io d s o f w a tc h s ta n d ln g (F ig u re 6 ). [ t Is dxiring t h i s l a t e r p e r io d o f w atch t h a t th e a r o u s a l l e v e l o f w a tc h s ta n d e r s would n o r m a lly be l o w e s t , and t h e r e f o r e in c r e a s e d e n v ir o n m e n ta l s t i m u l a t i o n would be moat e f f e c t i v e . D uring th e f i r s t q u a r te r hour o f w atch t h e r e was no d i f f e r e n c e in perform ance under v a r i e t y and c o n t r o l c o n d i t i o n s b e c a u se the Ss under o o n t r o l c o n d i t i o n s were s t i l l s u f f i c i e n t l y aroused to m a in ta in e f f i c i e n t perform ance . 61* The e f f e c t o f v a r i e t y s t i m u l a t i o n as a f u n c t i o n o f tim e on w a tch was d i f f e r e n t in th e second e x p e r im e n t. T h at i s , th e v a r i e t y s t i m u l a t i o n was l e a s and l e s s e f f e c t i v e a s th e w a tch p r o g r e s s e d ( F i g u r e 13)• On th e s u r f a c e , t h i s r e s u l t w ould a p p e a r to be c o n t r a r y t o w hat would be p r e d i c t e d from t h e a r o u s a l t h e o r y . An e x p l a n a t i o n i s a f f o r d e d by th e r e l a t i v e d u r a t i o n s o f tim e t h a t th e Ss a c t u a l l y s p e n t l o o k i n g a t the albums ( r e c e i v i n g v a r i e t y s t i m u l a t i o n ) as a f u n c t i o n o f tim e on w a tc h . At th e end o f th e e x p e rim e n t e ach S was i n t e r v i e w e d and asked to e s t i m a t e f o r each f i f t e e n m in ute p e r i o d of w a tc h the amount o f tim e he s p e n t lo o k in g th r o u g h th e album. The r e s u l t was t h a t th e a v e ra g e S s p e n t o n l y o n e - t h i r d as much tim e l o o k i n g a t the albums d u r i n g the l a s t f i f t e e n m in u te s a s he did d u r i n g th e f i r s t f i f t e e n m i n u t e s . T hat i s , he r e c e i v e d f a r l e s s v a r i e t y s t i m u l a t i o n d u r i n g the l a t e r p e r i o d s o f w a tch t h a n he d id d u r i n g th e e a r l i e r p e r i o d s o f w a tch . I t can be seen in F ig u r e 1^> t h a t t h e r e was a d i r e c t r e l a t i o n s h i p betw een t h e amount o f v a r i e t y s t i m u l a t i o n r e c e i v e d and th e amount o f improvement under v a r i e t y s t i m u l a t i o n . Thus th e f a c t o f d e c r e a s e d e f f e c t i v e n e s s o f v a r i e t y s t i m u l a t i o n as a f u n c t i o n o f tim e on w atch can be e x p la in e d in term s o f th e d e c r e a s e d amount o f such s t i m u l a t i o n , and I s t h e r e f o r e c o n s i s t e n t w i t h the a r o u s a l t h e o r y . A r e l a t i o n such as t h a t shown in M E A N N UM BER o F MINUTES SPENT LOOKING A T ALBUMS 6 5 10( 9 a t 7 6 5 h 3 0 \ Q t Amount o f v a r i e t y s t i m u l a t l o n Amount of improvement© with variety stimulation 0 15 30 ii5 60 MINUTES OF WATCH F ig u r e l £ . Time s p e n t lo o k in g a t albums and d i f f e r e n c e in p e rc e n t a g e o f d e t e c t i o n s on v a r i e t y and c o n t r o l w atches as a f u n c t i o n o f time on w atch (N = 1 8 ). 20 18 16 lU 12 10 8 6 1 * 2 0 DIFFERENCE BETW EEN PERCENTAGE OF DETECTIONS O N VARIETY A N D CONTROL WATCHES 6 6 F ig u re 15 would seem to be c o m p le te ly i n c o n s i s t e n t w ith the f i l t e r t h e o r y . An A r o u s a l - F l l t e r Theory B ro a d b en t h a s s a i d i n a p e r s o n a l com m unication and e ls e w h e re (B ro a d b e n t, 1953) t h a t he f a v o r s b o th an a r o u s a l and a f i l t e r t h e o r y . The o v e r - a l l l e v e l o f p erform an ce i s d e te rm in e d by a r o u s a l and e x p e c ta n c y , b u t the d e o l i n e in p erfo rm an ce d u r i n g w atch i s d e te rm in e d by th e i n c r e a s i n g fre q u e n c y o f f i l t e r d e v i a t i o n s . He su g g e s te d t h a t th e e x tr a n e o u s s t i m u l i u se d in th e p r e s e n t stu d y would have b o t h a r o u s a l and d i s t r a c t i o n e f f e c t s , but because o f the n a t u r e o f th e t a s k th e a r o u s a l e f f e c t s would overshadow or c a n c e l o u t the d i s t r a c t i o n e f f e c t s . B roadb ent p r e d i c t e d t h a t v i g i l a n c e p erfo rm an ce u n d e r th e v a r i e t y and c o n t r o l c o n d i t i o n s would e i t h e r show no d i f f e r e n c e or a s l i g h t improvement w i t h the v a r i e t y c o n d i t i o n s . B r o a d b e n t 's t h e o r e t i c a l p o s i t i o n , t h e r e f o r e , i n c o r p o r a t e s b o t h the a r o u s a l and the f i l t e r c o n c e p ts ; and the p r e d i c t e d outcome o f e x p e r im e n ts l i k e th o se r e p o r t e d h e r e would depend upon which c o n c e p t were dom inant under th e e x p e r im e n ta l c o n d i t i o n s u s e d . R e g a r d le s s o f th e o u t come a combined a r o u s a l - f l i t e r t h e o r y could a cc o u n t f o r th e r e s u l t s by e m p h a siz in g one c o n ce p t or th e o t h e r . Such a th e o r y would t h e r e f o r e be d i f f i c u l t to t e s t . Although Broadbent correctly predicted the 67 f a c i l i t a t i n g e f f e c t o f th e v a r i e t y o c n d l t i o n s used In t h i s s t u d y from a combined a r o u s a l - f 11 t e r t h e o r y , i t sh o u ld be n o t e d t h a t an a c c u r a t e p r e d i c t i o n was a l s o p r o v id e d by an a r o u s a l t h e o r y a l o n e . I t would seem s u p e r f l u o u s to In clu de th e f i l t e r o o n c e p t In a c c o u n t i n g f o r the r e s u l t s when th e a r o u s a l t h e o r y a lo n e can a c c o u n t f o r them . The more p a rs im o n io u s e x p l a n a t i o n i s i n term s o f an a r o u s a l t h e o r y and n o t a d u a l a r o u s a l - f 11 t e r t h e o r y . T here was a t l e a s t one r e s u l t o f th e p r e s e n t s tu d y t h a t was I n c o n s i s t e n t w i t h B r o a d b e n t ’s combined m odel. I t la d u r i n g th e l a t e r p e r i o d s o f w a tch t h a t th e d i s t r a c t i o n e f f e c t ( f i l t e r f l u c t u a t l o n s ) Is supposed t o be g r e a t e s t , and t h e r e f o r e th e a d v a n ta g e o f a r o u s a l s h o u ld d e c r e a s e as tim e on w atch p r o g r e s s e s . Yet F i g u r e 6 shows t h a t th e o p p o s i t e was o b s e r v e d - - t h e a d v a n ta g e u n d e r v a r i e t y c o n d i t i o n s was g r e a t e s t d u r i n g the l a t e r p e r i o d s of w a tc h . The r e s u l t s shown in F i g u r e 13 a re c o n s i s t e n t w i t h th e combined m od el, b u t t h e s e r e s u l t s have a l r e a d y been e x p l a i n e d in term s o f th e a r o u s a l t h e o r y (se e F*lgure l £ ) . S u g g e s t i o n s f o r F u r t h e r R e s e a r c h B ro a d b e n t s u g g e s t e d t h a t th e f i l t e r f l u c t u a t i o n s would have a more pron ou nced e f f e c t on v i g i l a n c e p e r f o r m ance I f th e t a s k s t i m u l i and th e I n t e r s t i m u l u s i n t e r v a l a re o f b r i e f d u r a t i o n . A more p r e c i s e t e s t of th e f i l t e r t h e o r y th a n th e p r e s e n t one would be a f f o r d e d by a 68 r e p e t i t i o n o f th e p r e s e n t e x p e r im e n ts w i t h the added In d ep e n d en t v a r i a b l e s o f s t i m u l u s d u r a t i o n ^.id i n t e r - s t l m u l u s i n t e r v a l d u r a t i o n * The p r e d i c t i o n from the f i l t e r t h e o r y would be t h a t p erfo rm an ce u n der v a r i e t y c o n d i t i o n s would show l e s s improvement ( o r would a c t u a l l y be p o o r e r ) over c o n t r o l c o n d i t i o n s when the s tim u lu s d u r a t i o n i s s h o r t or when th e l n t e r s t l m u l u s i n t e r v a l I s of b r i e f d u r a t i o n . The a r o u s a l h y p o t h e s i s p o s t u l a t e s a c u r v i l i n e a r r e l a t i o n s h i p betw een l e v e l o f a r o u s a l and l e v e l o f respo nse e f f i c i e n c y . That I s , p erform an ce w i l l be a d v e r s e l y a f f e c t e d by e i t h e r too h ig h or too low a l e v e l o f a r o u s a l . T h e r e f o r e , in f u r t h e r t e s t s o f the a r o u s a l h y p o t h e s i s as i t r e l a t e s to v i g i l a n c e p erfo rm an ce i t would be d e s i r a b l e to v a ry the i n t e n s i t y o f th e a c t i v a t i n g s t i m u l i o v e r a wide ran g e w ith o b s e r v a t i o n o f p erform ance under a t l e a s t t h r e e l e v e l s o f a r o u s a l . I f th e r e s u l t s v e r i f y the assum p tio n of c u r v i l l n o a r l t y , th e y w i l l o f f e r s t r o n g a d d i t i o n a l su p p o rt f o r th e a r o u s a l th e o r y o f v i g i l a n c e . CHAPTER V II SUMMARY Purpose Research has repeatedly demonstrated that when human observers are required to monitor displays for prolonged periods of time under monotonous conditions of work their detection ^ -rformance typically declines as time on watch progresses. A number of theoretical approaches to the exDlanation of this decrement have been offered, but little effort has been made to Identify and clarify the discrepancies between these theories. The purpose of the present study was to test hypotheses derived from two theories of vigilance and to provide additional empirical facts that may aid In the eventual understandIng and control of human monitoring behavior. The Problem The theories from which the hypotheses were derived were the "filter” theory and the "arousal" theory. The filter theory (Broadbent, 1959) accounts for the vigilance decrement by proposing that the human observer during a monotonous vigil will tend more and more to 69 70 s e l e c t I r r e l e v a n t I n f o r m a t i o n from h i s e n v iro n m e n t as tim e on w a tch p r o g r e s s e s . When a t t e n d i n g to I r r e l e v a n t a s p e c t s o f h i s e n v i r o n m e n t , th e o b s e r v e r w i l l be u n a b le to p r o c e s s r e l e v a n t t a s k I n f o r m a t i o n and, t h e r e f o r e , w i l l t e n d to m iss an i n c r e a s i n g number o f c r i t i c a l s i g n a l s as th e w atch p r o c e e d s . The a r o u s a l t h e o r y (Hebb, 19^i?) p r o p o s e s t h a t e f f i c i e n t r e s p o n s e b e h a v io r I s d e p e n d e n t upon an o p tim a l l e v e l o f c o r t i c a l a r o u s a l . The l e v e l of a r o u s a l Is in t u r n d e p e n d e n t upon a v a r i e t y o f s t i m u l u s I n p u t , w h e th er t h a t s t i m u l a t i o n be r e l e v a n t or I r r e l e v a n t to th e t a s k a t ha n d . The o b se rv e d d e c re m e n t In p e rfo rm a n c e on monotonous v i g i l a n c e t a s k s I s a p r o d u c t o f low ered a r o u s a l r e s u l t i n g from the c o n tin u e d I n v a r i a n c e of e n v lr o n m e n ta l s t i m u l a t i o n d u r i n g w a t c h s t a n d l n g . The r e s e a r c h r e p o r t e d h e re was d e s ig n e d as a t e s t o f o p p o s in g p r e d i c t i o n s d e r i v e d from t h e s e two t h e o r i e s . The e x p e r i m e n t a l s i t u a t i o n i n v o lv e d w a t c h s t a n d l n g In an e n v iro n m e n t c o n t a i n i n g a s o u rc e of I r r e l e v a n t s t i m u l a t i o n co m p etin g w i t h th e s o u r c e o f s i g n a l s to be d e t e c t e d compared w i t h w a t c h s t a n d l n g In t h e a b se n c e of co m p eting s t i m u l a t i o n . The p r e d i c t i o n d e r i v e d from the f i l t e r th eo ry was t h a t the o b s e r v e r would te n d to s e l e c t th e c o m p e tin g , I r r e l e v a n t i n f o r m a t i o n and th u s would m iss more s i g n a l s when such s t i m u l a t i o n was p r e s e n t th a n when i t was a b s e n t . The p r e d i c t i o n d e r i v e d from the a r o u s a l t h e o r y was t h a t 71 th e com peting s t i m u l a t i o n would add to t h e v a r i a b i l i t y of th e e n v ir o n m e n t , i n c r e a s e a r o u s a l , and th u s r e s u l t in improved d e t e c t i o n p e rfo rm an c e . The E xp erim en tal H y p o th e sis The h y p o t h e s i s t e s t e d i n the p r e s e n t s tu d y was s t a t e d in te rm s o f the p r e d i c t i o n from th e a r o u s a l t h e o r y , b e c a u se th e p r e s e n t i n v e s t i g a t o r has found t h a t th e o r y to be more c o n v in c in g . The h y p o t h e s i s was: W a tc h s ta n d e rs w i l l d e t e c t a g r e a t e r p e r c e n t a g e of s i g n a l s when a v a r i e t y o f s t i m u l a t i o n i s p r e s e n t i n the e n v iro n m en t th a n i n th e absence o f such v a r i e t y , even though the i n c r e a s e d v a r i a b i l i t y has no r e l e v a n c e f o r th e v i g i l a n c e t a s k b e in g p e rf o r m e d . The i n v e s t i g a t i o n was c a r r i e d ou t in two p h a s e s . In th e f i r s t p h a se , an e x p e rim e n t was c o n d u cted to t e s t the e f f e c t s o f e x tr a n e o u s a u d i t o r y s t i m u l a t i o n on v i s u a l v i g i l a n c e p e rfo rm a n c e . In the second p h a s e , an e x p e rim e n t was co nducted to t e s t th e e f f e c t s o f e x tr a n e o u s v i s u a l s t i m u l a t i o n on a u d i t o r y v i g i l a n c e p e rfo rm an c e . Experiment I Method. In th e f i r s t e x p e rim e n t f o u r t e e n sonarmen and f o u r t e e n c a s u a l n a v a l p e r s o n n e l se rv ed in two o n e -h o u r w a tc h s t a n d ln g s e s s i o n s eac h day f o r f o u r d a y s . T h e ir t a s k was to d e t e c t s l i g h t in c r e m e n ts in the b r i g h t n e s s of an I n t e r m i t t e n t l i g h t . These i n c r e m e n ts , c a l l e d " s i g n a l s , " o c c u r r e d a t random I n t e r v a l s a t an a v e ra g e r a t e o f ?l± s i g n a l s p e r h o u r . The s i g n a l s were d e te rm in e d i n a p r e l i m i n a r y s tu d y to be d e t e c t a b l e w ith 90 % a c c u ra c y u nd er a l e r t e d c o n d i t i o n s . Each w a tch was p re c e d e d by a b r i e f warm-up s e s s i o n and a tw o-m inu te p r e t e s t and was fo llo w e d by a tw o-m inute p o s t t e s t . The Ss s to o d w atch i n grou ps of seven men, each a s s i g n e d to a s e p a r a t e w a t c h s ta n d ln g b o o th . Whenever an S o b se rv e d a s i g n a l he r e p o r t e d h i s d e t e c t i o n by p r e s s i n g a h a n d - h e ld s w it c h . A ll r e s p o n s e s and s i g n a l o c c u r r e n c e s were r e c o r d e d on an E s t e r l i n e - a n g u s pen r e c o r d e r . The in d e p e n d e n t v a r i a b l e in the f i r s t e x p e rim e n t was the c o n d i t i o n o f a u d i t o r y s t i m u l a t i o n d u r in g v i s u a l w a t c h s t a n d l n g . On f o u r o f th e e i g h t s e s s i o n s w h ite n o i s e was p r e s e n t e d th ro u g h a s p e a k e r mounted above th e v i s u a l d i s p l a y . On the o t h e r f o u r s e s s i o n s a v a r i e t y o f a u d i t o r y s t i m u l a t i o n (m usic, c o n v e r s a t i o n , m ec h an ica l n o i s e s ) was p r e s e n t e d th ro u g h the s p e a k e r . In a l l c a s e s the a u d i t o r y s t i m u l a t i o n was u n r e l a t e d to th e o c c u r r e n c e o f s i g n a l s on th e v i s u a l d i s p l a y . The e x p e r i m e n t a l c o n d i t i o n s were c o u n te r b a l a n c e d f o r the e f f e c t s o f time o f day, p r a c t i c e , and w a t o h s t a n d i n g b o o th . The d e p en d e n t v a r i a b l e was the p e r c e n t a g e of s i g n a l s d e t e c t e d . R e s u l t s . The r e s u l t s o f the f i r s t e x p e rim e n t were 73 1* The p e r c e n t a g e o f s i g n a l s d e t e c t e d by a l l Ss on a l l w atch es d e c l i n e d a s a f u n c t i o n o f tim e on w atch . P erform ance d e c l i n e d r a p i d l y from the p r e t e s t t o th e b e g in n in g o f the main w a to h , c o n tin u e d t o d e c l i n e d u r i n g th e f i r s t h a l f hour o f w atoh , and rem ained s t a b l e a t a red u ced l e v e l t h e r e a f t e r . On th e p o s t t e s t , p e rfo rm an c e r e c o v e r e d a b r u p t l y and c o m p le te ly to th e p r e t e s t l e v e l . 2 , A s i g n i f i c a n t l y g r e a t e r p e rc e n t a g e o f s i g n a l s were d e t e o t e d u n d e r c o n d i t i o n s of v a r i e t y a u d i t o r y s t i m u l a t i o n th an u n d e r w h i t e n o i s e c o n d i t i o n s ( p ^ . 0 0 1 ) . The Improvement u nd er v a r i e t y c o n d i t i o n s was g r e a t e s t d u r i n g th e l a s t q u a r t e r ho u r o f th e w a t c h s t a n d in g p e r i o d . 3. D e t e c t i o n p erfo rm an ce improved w i t h p r a c t i c e u n d e r a l l e x p e r im e n ta l c o n d i t i o n s (p< .0 0 1 ) . 1*. There was no s i g n i f i c a n t i n t e r a c t i o n between th e e f f e c t s o f a u d i t o r y c o n d i t i o n s and p r a c t i c e on the v i s u a l t a s k . 5. There was no s i g n i f i c a n t d i f f e r e n c e betw een perfo rm an c e on m orning and a f t e r n o o n w a tc h e s . 6 . The d e t e o t l o n p erfo rm an ce of sonarmen was m a rk e d ly s u p e r i o r to t h a t of c a s u a l n a v a l p e r s o n n e l . E xperim ent I I Method. Eighteen sonarmen served in two one-hour watchstandlng sessions each day for two days. Their task was to detect a slight increment in the loudness of an intermittent 750 cps pure tone presented over headphones. The signals occurred at random intervals at a rate of signals per hour, and were determined in a preliminary study to be detectable with 90« accuracy under alerted conditions. On two of the four sessions the 3s were 71* p e r m i t t e d to lo o k t h r o u g h l a r g e albums o f p h o to g r a p h s w h i l e m o n i t o r i n g th e a u d i t o r y d i s p l a y . On t h e o t h e r two w a tc h e s th e Ss m o n ito re d th e d i s p l a y w i t h o u t t h e p h oto a lb u m s. The w a t c h s t a n d l n g p r o c e d u r e was t h e same a s t h a t used in th e f i r s t e x p e r i m e n t . R e s u l t s . The r e s u l t s o f t h e second e x p e r im e n t w e r e : 1. The d e t e c t i o n p e rfo rm a n c e o f a l l Ss u n d e r a l l c o n d i t i o n s d e c l i n e d a s a f u n c t i o n o f tim e on w atoh and r e c o v e r e d c o m p l e t e ly on th e p o a t t e s t . 2. A s i g n i f i c a n t l y g r e a t e r p e r c e n t a g e o f s i g n a l s were d e t e c t e d when th e Ss sto o d w a tch w i t h th e p h o to albums th a n when they sto o d w a tc h w i t h o u t th e albums (p . 0 2 5 ) . The improvement w i t h th e p h o to albums was g r e a t e s t d u r i n g th e f i r s t q u a r t e r ho u r o f th e w a t o h s t a n d l n g p e rio d * 3. D e t e c t i o n p e rfo rm a n c e Improved w i t h p r a c t i c e u n d e r a l l e x p e r i m e n t a l c o n d i t i o n s ( p - . 0 2 5 ). 1*. There was no s i g n i f i c a n t I n t e r a c t i o n betw een th e e f f e c t s o f v i s u a l c o n d i t i o n s and p r a c t i c e on th e a u d i t o r y t a s k . c; T here was no s i g n i f i c a n t d i f f e r e n c e betw een p e rfo rm a n c e on m orning and a f t e r n o o n w a to h e s . 6 . Ss te n d e d to spend l e s s tim e l o o k in g a t th e albums a s th e w a tc h p r o g r e s s e d . There was a d i r e c t r e l a t i o n s h i p b etw een th e amount o f tim e t h e Ss s p e n t l o o k i n g a t t h e albums and t h e amount o f Improvem ent In d e t e c t i o n p e rfo rm a n c e w i t h th e album s. C o n c lu s io n s The r e s u l t s o f b o t h e x p e r i m e n t s i n d i c a t e d t h a t an i n c r e a s e In th e v a r i a b i l i t y of th e e n v ir o n m e n ta l stim ulation 7 5 had a f a c i l i t a t i n g e f f e c t on d e t e c t i o n p e rfo r m a n c e . The e x p e r i m e n t a l h y p o t h e s i s , t h e r e f o r e , was c o n firm e d i n b o t h i n s t a n c e s . These r e s u l t s were t a k e n as o o u n te r e v ld e n o e f o r a f i l t e r t h e o r y o f v i g i l a n c e and a s s u p p o r t f o r an a r o u s a l t h e o r y o f v i g i l a n c e . REFERENCES REFERENCES Adams, J . A. V i g i la n c e I n th e d e t e c t i o n o f l o w - i n t e n s l t y v i s u a l s t i m u l i . J . e x p. P s y c h o l . . 1956, £ 2 , ?0l|.-208. B aker, C. H. V i g i la n c e d e crem e n t a s a f u n c t i o n o f r e g u l a r i t y o f l n t e r - s l g n a l i n t e r v a l s . D efense R esearch M edical Lab. Memo. . F e b . , 1956. B ro a d b e n t, D. E. C l a s s i c a l c o n d i t i o n i n g and human w atch - k e e p in g . P s y c h o l. R ev. , 1953&» 60# 331-339* B ro a d b e n t, D. E. N o ise , paced p e rfo rm an c e and v l g i l a n o e t a s k s . B r i t . J . P s y c h o l . . 1953b, 4k» ?9 5 -3 0 3 . B ro a d b e n t, D. E. A M echanical model f o r human a t t e n t i o n and Immediate memory. P s y c h o l. Roy. , 1967, bit.. 205-216. B ro a d b e n t, D. E. 1 c r e e p t I o n and co m m u n icatio n . Dor.don: Pergamon P r e s s , B uckner, D. N ., H a r a b e d la n , A ., and McGrath, J. J . A stud y o f I n d i v i d u a l d i f f e r e n c e s In v i g i l a n c e p e r f o r m a n c e . ^os A n g e les: Ffuman F a c to r s '" R e s e a rc h , I n c . , Doese, J. Some problem s in th e th e o r y of v i g i l a n c e . P s y c h o l . R ev. . 1956, 6 2, 3 59-3b8. Deeae, J . and Ormond, E* S t u d i e s o f d e t e c t a b i l i t y d u r i n g c o n tin u o u s v i s u a l s e a r c h . WAPD Tech. Rep, 5 3 - 6 . 1953. Frankmann, J . P. and Adams, J, A. T h e o r ie s o f V i g i l a n c e , T e c h n ic a l Note A7C C D D -TN -6o-26, A v i a ti o n Psvch. L ab .. 7KI7."of T l l l n V i 1966.--------- F r a s e r , D. C. The r e l a t i o n o f an e n v ir o n m e n ta l v a r i a b l e to p erfo rm an ce in a p ro lo n g ed v i s u a l t a s k . Q u a rt. J . e x p. P s y c h o l. , 1953, 31-3 G arvey, W, D ., O u lle d g e , I . , and Henson, J . B. E f f e c t of l e n g t h o f o b s e r v i n g time on th e v i s u a l t h r e s h o l d f o r d e t e c t i n g a f a i n t s a t e l l i t e . S c i e n c e , 1^68, 127, 1 7 /o -l? U * . 77 78 G arvey, W. D. , T a y l o r , F. V., and Newlln, E. P. The use o f " a r t i f i c i a l s i g n a l s " to enhance m o n it o r i n g p e rfo rm a n c e . NRL R e p o rt 5 2 6 9 . 1959* Hebb, D. 0 . D riv e s and th e c o n c e p tu a l n e rv o u s system . P sy c h o l. R ev. , 1955. 62. 2l;3-?53* Hebb, D. 0 . A te x tb o o k o f p s y c h o lo g y . P h i l a d e l p h i a : Saunders d o . , 1958. H o lla n d . J . G. Human v i g i l a n c e . S c i e n c e . 1958, 1 2 8 , 6 1 -6 7 . Howland, D. An I n v e s t i g a t i o n o f the p e rfo rm an c e o f the human m o n ito r in the man-machine system , (an a p p l i c a t i o n f o r g r a n t o f r e s e a r c h f u n d s ) . Ohio S t a t e U n i v e r s i t y , Columbus, Ohio, May, i 9 6 0 . J e n k i n s , H. M. The e f f e c t o f s i g n a l r a t e on p erfo rm ance in v i s u a l m o n it o r i n g . Am. J . P s y c h o l ., 1958, 71. 6I4 7 — 6 6 1 . ------- ---------- --------- J e r i a o n , H. J. E x p erim en ts on v i g i l a n c e : d u r a t i o n of v i g i l and the d ecrem ent f u n c t i o n . WADD Tech. R ept. sfl-3 6 9 . 1 9 5 s. Kappauf, W . E. and Powe, W. E. Perform ance decrem en t on an a u d i o - v i s u a l c h e c k in g t a s k . J . exp. P s y c h o l . , 1959, 5 2 , 1*9-56. L i n d q u i s t , E. F. D esign and a n a l y s i s o f e x p e r im e n ts in p sy c h o lo g y and e d u c a t i o n . B o sto n : Hougnton W I f f i l n , Mackworth, N. H. R e se a rc h e s on the m easurement of human p e rfo rm a n c e . M edical R e se a rc h Council S p e c i a l R eport S e r i e s No. 268" 1^56* Mackworth, N. H. V i g i la n c e . Advancement o f S c i e n c e , 1Q57, 5 2 . 3 8 Q - 3 9 3 . McCormack, P. D. Perform ance i n a v i g i l a n c e ta s k as a f u n c t i o n o f i n t e r - s t i m u l u s I n t e r v a l and I n t e r p o l a t e d r e s t , Canadian J. P s y c h o l . , 1958, 12 , 3l;?-?i*o. M cFarland, R. A ., Holway, A. N ., and H u rv ich , L. M . S t u d i e s o f v i s u a l f a t i g u e . Cambridge: Harvard Graduate S c h o o l ' o f B u s in e s s A d m i n i s t r a t i o n , 191.2* 79 McGrath, J. J. , H a r a b e d ia n , A . , and B u c k n er, D. N. Review and c r i t i q u e o f th e l i t e r a t u r e on v i g i l a n c e p e r f o r m a n c e . Los A n g e l e s : Human f a c t o r s R e s e a r c h , I n c . , McGrath, J . J . , H a r a b e d ia n , A ., and B u ck ner, D. N. An e x p l o r a t o r y s t u d y o f th e c o r r e l a t e s o f v i g i l a n c e f e r T o r a a n c e . Los A n g e le s : human F a c t o r s R e s e a rc h , n c . , i 9 6 0 . M oruezi, G. , and Magoun, H. W. B r a in stem r e t i c u l a r f o r m a t io n and a c t i v a t i o n o f th e EEQ. EEG c l l n . H e u r o p h y s l o l . , 191*9, 1, 1*55-1*73. P o l l a c k , I . and K n a ff, P. R. M ain ten ance o f a l e r t n e s s by a lou d a u d i t o r y s i g n a l . J . a c o u s t i c a l Soc. Amer., 1958, JO , 1013-1 01 6. S am uels, I . R e t i c u l a r m echanisms and b e h a v i o r . P s y c h o l. B u l l . , 1959, 5 6 , 1 -2 5 . S o la n d t , D, Y. and P a r t r i d g e , D. M. R esearch on a u d ito r y pro blem s p r e s e n t e d by n a v a l o p e r a t i o n s , J. Canad. Med. S e r v i c e s , 19^*6, J , 3 2 3 -3 7 9 . W lt t e n b u r g , J . A ., R oss, S., and Andrew, T. G. Sustained p e r c e p t u a l e f f i c i e n c y as m easured by th e c lo c k t e s t . P e r c . Motor S k i l l s , 1956, 6 , 10 9 -1 1 6 . APPENDICES APPENDIX I PRELIMINARY PSYCHOPHYSICAL STUDIFS The s t u d i e s d e s c r i b e d h e re were made p r i o r to th e main e x p e r im e n ts . T h e ir p u rpo se was to p r o v id e a s p e c i f i c a t i o n o f the d e t e c t a b i l i t y o f the v i s u a l and a u d i t o r y s i g n a l s used in the main e x p e r im e n ts in term s of the b r i g h t n e s s and lo u d n e s s d i s c r i m i n a t i o n t h r e s h o l d s o f th e Ss. The method was th e same in b o t h s t u d i e s . Method S u b j e c t s . The t w e n t y - e i g h t Ss who were used in E xp erim ent I p a r t i c i p a t e d in th e b r i g h t n e s s d i s c r i m i n a t i o n s t u d y . The e i g h t e e n Ss who were used in E xp erim ent II p a r t i c i p a t e d in the l o u d n e s s d i s c r i m i n a t i o n s t u d y . D i s p l a y . The d i s p l a y s were the same as th o se used in th e main e x p e r i m e n t s : th e i n t e r m i t t e n t l i g h t and th e i n t e r m i t t e n t to n e . S t i m u l i . For each mode, s t a n d a r d and com parison s t i m u l i were u s e d . The s t a n d a r d s t i m u l u s f o r the b r i g h t n e s s d i s c r i m i n a t i o n t a s k was a l i g h t o f th e same b r i g h t n e s s as th e background s t i m u l i in the v i s u a l v i g i l a n c e t a s k . The s t a n d a r d s t i m u l u s f o r the lo u d n e s s d i s c r i m i n a t i o n t a s k was a tone o f th e same lo u d n e s s as th e background s t i m u l i i n th e a u d i t o r y v i g i l a n c e t a s k . For b o t h th e b r i g h t n e s s and l o u d n e s s s t u d i e s * t e n d i f f e r e n t com parison s t i m u l i were u s e d . Each com parison s t i m u l u s The method u sed h e re was t h a t used in an e a r l i e r s t u d y by McGrath, H a ra b e d ia n , and Huckner (19&0). 81 8 2 was p r o g r e s s i v e l y more i n t e n s e { b r i g h t e r o r lo u d e r ) th a n th e c o r r e s p o n d i n g s t a n d a r d s t i m u l u s . Both the s t a n d a r d and th e c o m p a riso n s t i m u l i were one second in d u r a t i o n . S tim u lu s p r e s e n t a t i o n . The s t a n d a r d s t i m u l u s was p a i r e d 26 tim e s wliJ7 e a c h o f t h e 10 c om pariso n s t i m u l i , m aking a t o t a l o f 200 r e q u i r e d d i s c r i m i n a t i o n s on each mode. S t i m u l i were p r e s e n t e d In p a i r s w i t h a 2-se co n d I n t e r v a l betw een th e s t i m u l i In e a c h p a i r and a $-*second I n t e r v a l betw een s e p a r a t e p a i r s . The s t a n d a r d s t i m u l u s a p p ea re d i n e ach p a i r . I t was f i r s t 50% o f th e tim e , and second $0% o f th e t im e . The p a i r s were random ly p r e s e n t e d i n g roups o f 20 p a i r s . W ith in each g ro u p , e v e r y c o m p a ri son s t i m u l u s a p p e a re d t w i c e , and was t h e f i r s t member o f t h e p a i r one time and th e second member th e o t h e r tim e . The p r e s e n t a t i o n o f 20 p a i r s to o k a b o u t t h r e e m in u te s . The Ss w ere allo w ed a 2 -m in u te r e s t p e r i o d betw een each group o f 20 p a i r s , w i t h a h a l f - h o u r r e s t betw een th e f i f t h and th e s i x t h g ro u p . The S s ' t a s k . The Ss were r e q u i r e d to judge the b r i g h t n e s s o r lo u d n e s s d i f f e r e n c e s betw een e a c h p a i r of s t i m u l i . They r e p o r t e d each Judgment by m arking on an answer s h e e t w h e th e r th e second s t i m u l u s was more i n t e n s e o r l e s s i n t e n s e ( b r i g h t e r v e r s u s dimmer o r lo u d e r v e rs u s s o f t e r ) th a n th e f i r s t s t i m u l u s in each p a i r . T e s t i n g - c o n d i t i o n s . The b r i g h t n e s s and lo u d n e s s d i s c r i m i n a t i o n t e s t s were con du cted in th e w a tc h s t a n d ln g b o o th s used in th e main e x p e r i m e n t s . The p r o c t o r was p r e s e n t in the room and c a l l e d o f f th e item numbers to the S s . R e s u l t s Brightness discrimination. The tests were first conducted using the fourteen casual personnel comprising Groups A and B. Data analysis indicated that the largest brightness difference (comparison stimulus 10 versus standard stimulus) was correctly discriminated only 1 1 % of the time. In testing the fourteen sonarmen comprising Groups C and D, therefore, two additional comparison 83 s t i m u l i were used end th e t h r e e m ost d i f f i c u l t com parison s t i m u l i w ere e l i m i n a t e d . The r e s u l t s a re shown in F ig u r e 16. With th e e x c e p ti o n of com parison s t i m u l u s 1, p e r c e n t a g e o f c o r r e c t d i s c r i m i n a t i o n s was a m onotonic f u n c t i o n o f th e b r i g h t n e s s d i f f e r e n c e betw een th e c o m p a ri son and - t a n d a r d s t i m u l i . Data p o i n t s a r e shown s e p a r a t e l y f o r the c a s u a l p e r s o n n e l and f o r the sonarmen b e ca u se o f th e d i f f e r e n c e s in b r i g h t n e s s d i s c r i m i n a t i o n t h r e s h o l d s betw een t h e s e g r o u p s , b u t th e mean p e r c e n ta g e c o r r e c t v a lu e i s f o r a l l Ss. The 90 c o r r e c t d e t e c t i o n p o i n t was used to I d e n t i f y the s i g n a l i n t e n s i t y to be used in the main e x p e rim e n t. A sim p le l i n e a r e x t r a p o l a t i o n was made to e s t a b l i s h t h i s p o i n t , and Is i n d i c a t e d in F ig u r e ID as a d o t t e d l i n e . Loudness d i s c r i m i n a t i o n . The r e s u l t s o f the l o u d n e ss d i s c r i m i n a t i o n t e s t s are shown In F ig u re 17. P e rc e n ta g e o f c o r r e c t l o u d n e s s d i s c r i m i n a t i o n s was a m onotonic f u n c t i o n o f the i n t e n s i t y o f th e com parison s t i m u l u s . The p o i n t on th e com parison s t i m u l u s I n t e n s i t y s c a l e t h a t c o rre s p o n d e d w i t h 90“ ^ c o r r e c t d i s c r i m i n a t i o n s was chosen as th e s i g n a l l e v e l to be used in E xperim ent I I , flu C O 55 O M ( r > < 55 O C O M « CO a tc o M cc C Q E - < o U 1 ffi ui o o u B Q m 100 90 BO 70 60 50 bo • Sonarmen o Casual perso nn el o o o Comparison Stimulus: ±, . L _ 5 i . . 6 . i . 7 i ... ft i . . 9 .. .i _ 10 S ig n a l Level i t 11 INTFNSITY OF COMPARISON STIMULUS ( A r b i t r a r y O nlts) Figure 1 6 . Mean p e r c e n t c o r r e c t b r i g h t ness d i s c r im i n a t io n s as a f u n c tio n of I n t e n s i t y of the comparison s tim u lu s showing e x t r a p o l a t i o n to the 00% s ig n a l d e t e c t i o n le v e l f o r llj s o n a r m e n and lli casual p e rs o n n e l. o Comparison Stimulus: S ig n a l Level b o 1 1 1 1 * ,l 1 } l 1 1 1 ? 3 ^ 5 o 7 89 INTENSITY OF COMPAHISuN STIMULUS (Arbitrary Units) F ig u re 17* Mean per c e n t c o r r e c t lo u d n ess d i s c r i m i n a t i o n s as a f u n c t i o n of I n t e n s i t y o f the comparison s tim u lu s f o r 1Q sonarmen. APPENDIX I I SIGNAL PRESENTATION SCHEDULES Table IX shows the occurrence of signals on the different schedules In terms of the number of stimuli between signals (Inclusive of the signal stimulus). All stimuli were presented at three-second Intervals. The four signal presentation schedules were eech played forward once and baclcward once In Experiment I. In Experiment II, only schedules and } were used. In that experiment one signal was added to schedule ? (between signals ll+ and 15) and one signal was eliminated from schedule 3 (signal t ?ij), so that the resulting rate was signals per watch. % 87 TABLE IX SIGNAL PRESENTATION SCHEDULES S i g n a l Number S c h e d u le 1 2 3 U 1 66 96 21 91 2 97 77 93 32 3 33 39 22 71 b 69 13 66 51 5 10 9 56 53 6 90 50 61 93 7 76 97 83 91 n 100 6 62 9 18 69 1 " 7 3 10 27 26 ?U 6 11 ?? 36 62 23 1? 66 20 91 11 V 9 69 13 h i i k 37 2? 95 22 15 20 06 36 13 16 99 56 7 5 62 17 78 6 81 61 19 59 23 U 87 19 °6 7? 32 6 20 98 86 100 91 21 60 07 15 62 22 9 1 U 3 33 2? ^1 71 81 ?b 1 * 72 36 0 6 6 ?6 13 27 37

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Creator Mcgrath, James Joseph (author)

Core Title The Effect Of Irrelevant Environmental Stimulation On Vigilance Performance

Degree Doctor of Philosophy

Degree Program Psychology

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

Tag OAI-PMH Harvest,psychology, experimental

Language English

Contributor Digitized by ProQuest (provenance)

Advisor Ruch, Floyd L. (committee chair), Michael, William B. (committee member)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c18-92712

Unique identifier UC11357683

Identifier 6101704.pdf (filename),usctheses-c18-92712 (legacy record id)

Legacy Identifier 6101704.pdf

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Document Type Dissertation

Rights Mcgrath, James Joseph

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

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

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