Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Activity of middle ear muscles under certain pure tone and noise conditions Hatch, Marion Beryl 1973

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1973_A6_7 H38_3.pdf [ 4.03MB ]
Metadata
JSON: 831-1.0101252.json
JSON-LD: 831-1.0101252-ld.json
RDF/XML (Pretty): 831-1.0101252-rdf.xml
RDF/JSON: 831-1.0101252-rdf.json
Turtle: 831-1.0101252-turtle.txt
N-Triples: 831-1.0101252-rdf-ntriples.txt
Original Record: 831-1.0101252-source.json
Full Text
831-1.0101252-fulltext.txt
Citation
831-1.0101252.ris

Full Text

ACTIVITY OF MIDDLE EAR MUSCLES UNDER CERTAIN PURE TONE AND NOISE CONDITIONS by MARION BERYL HATCH B . S c , U n i v e r s i t y • o f B r i t i s h Columbia, 1971 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the D i v i s i o n o f A u d i o l o g y and Speech S c i e n c e s i n the Department o f P a e d i a t r i c s We a c c e p t t h i s t h e s i s as conforming t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA August, 1973 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the requirements f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood t h a t c o p y i n g or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be allowed without my w r i t t e n p e r m i s s i o n . The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada Date (WMSJ- U.I'm A b s t r a c t T h i s i n v e s t i g a t i o n was concerned w i t h measurements o f middle ear muscle a c t i v i t y . S p e c i f i c a l l y , the i n v e s t i g a t i o n was d e s i g n e d : (a) .to compare r e f l e x t h r e s h o l d s f o r pure t o n e ( P T ) , octave band noise(OBN), and o n e - t h i r d o c t a v e band noise(TQBN); (b) t o stud y middle e ar muscle a c t i v i t y d u r i n g a f i v e minute exposure t o t h e s e s t i m u l i a t 114 dB SPL; and (c) t o compare middle e a r muscle a c t i v i t y f o r s t i m u l i o f d i f f e r e n t f r e q u e n c i e s . E i g h t e e n s u b j e c t s were d i v i d e d i n t o two groups. Group I s u b j e c t s were exposed t o a 700 Hz PT, t o OBN w i t h c e n t e r f r e q u e n c y 500 Hz, and TOBN w i t h c e n t e r f r e q u e n c y 630 Hz; Group I I s u b j e c t s were exposed t o a 1400 Hz PT, to OBN w i t h c e n t e r f r e q u e n c y 1000 Hz, and TOBN w i t h c e n t e r f r e q u e n c y 1250 Hz. A Madsen E l e c t r o a c o u s t i c Impedance B r i d g e and g r a p h i c r e c o r d e r were used t o r e c o r d impedance changes d u r i n g s t i m u l a t i o n w i t h the above s t i m u l i . These impedance changes were assumed t o r e f l e c t muscle a c t i v i t y . T h r e s h o l d s f o r the a c o u s t i c r e f l e x were determined u s i n g s t a n d a r d p r o c e d u r e s . A n a l y s i s o f r e s u l t s i n d i c a t e d muscle a c t i v i t y d e c r e a s e d p r o g r e s s i v e l y d u r i n g s t i m u l a t i o n . R e f l e x decay was s i g n i f i c a n t l y g r e a t e r f o r s t i m u l a t i o n w i t h PT than f o r s t i m u l a t i o n w i t h 0BN(Groups I and I I ) and TOBN(Group I I ) . I t was noted t h a t r e f l e x decay was l e s s d u r i n g s t i m u l a t i o n w i t h a 700 Hz PT than d u r i n g s t i m u l a t i o n w i t h a 1400 Hz PT. . - i i -F i n a l l y , i t was observed that r e f l e x thresholds were higher f o r P T than f o r OBN and TOBN . Decrease i n muscle a c t i v i t y during acoustic s t i m u l a t i o n was discussed i n terms of adaptation and p o s s i b l y c e n t r a l mechanisms; the c h a r a c t e r i s t i c s of the s t i m u l i were compared and discussed, as a p o s s i b l e explanation f o r d i f f e r e n c e s i n r e s u l t s obtained f o r tones and noise'. - i i i -Table of Contents Page Abstract • . i i L i s t of Tables v i L i s t of Figures v i i i Acknowledgment x Chapter 1 Introduction 1 Chapter 2 Review of the L i t e r a t u r e 3 Middle Ear Muscles and Acoustic Reflex . 3 Direct Observations of the Stapedius Muscle and Electromyography 9 Extratympanic' Manometry... . . 10 Equal Loudness Experiments 11 C o n t r a l a t e r a l Remote Masking(CRM) . . . 13. CRM produced by pure tones and noise . 1 3 CRM and middle ear muscle a c t i v i t y . . 14 Temporary Threshold Shift(TTS) 1 5 TTS produced by exposure to noise . . 1 5 TTS produced by pure tones and noise . 16 TTS and middle ear muscle a c t i v i t y . . 18 Acoustic Impedance Measurements . . . . 1 9 Impedance changes e l i c i t e d by pure tones 20 Impedance changes e l i c i t e d by noise . 22 Impedance changes e l i c i t e d by pure tones and noise 2 3 Size of e l i c i t e d impedance changes . 26 - i v -Page Chapter 3 Statement of the Problem 27 Chapter 4 Experimental Apparatus and Procedure . 29 Experimental Design 29 Subjects 32 Equipment 32 S i g n a l generation ..." 32 C a l i b r a t i o n 34 Impedance measurements 34 Procedure 35 Data Measurement 36 Chapter 5 Results . . ; 38 S t a t i s t i c a l Analysis 38 Threshold of the Acoustic Reflex . . 38 Reflex A c t i v i t y 40 Maximum si z e of pen d e f l e c t i o n . . 40 Reflex decay 45 • A c t i v i t y with time 45 R e l i a b i l i t y of Measurements 59 Chapter 6 Discussion and Conclusions 60 General Muscle A c t i v i t y 60 Threshold of the Acoustic Reflex . . 61 Reflex A c t i v i t y 62 Conclusions 68 Selected Bibliography 70 Appendix 75 -v- ~ L i s t of Tables Table Page I A n a l y s i s of Va r i a n c e : Threshold as a f u n c t i o n of c o n d i t i o n f o r the nine s u b j e c t s i n Group I . . . . 39 . I I A n a l y s i s of Varia n c e : Threshold as a f u n c t i o n of c o n d i t i o n f o r the nine s u b j e c t s i n Group I I 41 I I I Newman-Keuls Test: S i g n i f i c a n c e of d i f f e r e n c e s between t h r e s h o l d s f o r each c o n d i t i o n i n Group I I 41 IV A n a l y s i s of V a r i a n c e : I n i t i a l s i z e of the a c o u s t i c r e f l e x , as a f u n c t i o n of c o n d i t i o n f o r the nine s u b j e c t s i n Group I 44 V A n a l y s i s of V a r i a n c e : I n i t i a l s i z e of the a c o u s t i c r e f l e x , as a f u n c t i o n of c o n d i t i o n f o r the nin e s u b j e c t s i n Group I I 44 VI A n a l y s i s of V a r i a n c e : R e f l e x decay as a f u n c t i o n of c o n d i t i o n f o r the nine s u b j e c t s i n Group I 49 V I I Newman-Keuls Test: S i g n i f i c a n c e of d i f f e r e n c e s between r e f l e x decay f o r each c o n d i t i o n i n Group I 49 V I I I A n a l y s i s of V a r i a n c e : R e f l e x decay as a f u n c t i o n of c o n d i t i o n f o r the nine s u b j e c t s i n Group I I 50 IX Newman-Keuls Test: S i g n i f i c a n c e of d i f f e r e n c e s between r e f l e x decay f o r each c o n d i t i o n i n Group I I 50 X A n a l y s i s of V a r i a n c e : Muscle a c t i v i t y as a f u n c t i o n of time and c o n d i t i o n f o r the nine s u b j e c t s i n Group I 53 XI Newman-Keuls Test: S i g n i f i c a n c e of d i f f e r e n c e s between c o n d i t i o n s as a f u n c t i o n of time f o r Group I 54 X I I Newman-Keuls Test: S i g n i f i c a n c e of d i f f e r e n c e s i n muscle a c t i v i t y w i t h time f o r Group I 55 - v i -Table Page X I I I A n a l y s i s of V a r i a n c e : Muscle a c t i v i t y as a f u n c t i o n of time and c o n d i t i o n f o r the nine s u b j e c t s i n Group I I 57 XIV Newman-Keuls Test: S i g n i f i c a n c e of d i f f e r e n c e s between c o n d i t i o n s across a l l times f o r Group I I 57 XV Newman-Keuls Test: S i g n i f i c a n c e of d i f f e r e n c e s i n muscle a c t i v i t y w i t h time f o r Group I I " 58 - v i i -L i s t of F i g u r e s F i g u r e Page 1 Schematic i l l u s t r a t i o n of the t e n s o r tympani muscle . . . . . 4 2 Schematic of the st a p e d i u s muscle and the attachment of i t s tendon t o the neck of the stapes 4 3 Diagram of presumed course of a c o u s t i c s t a p e d i u s r e f l e x a r c 7 4 Outward drum movement caused by a c o u s t i c s t i m u l a t i o n . Muscle r e l a x a t i o n d u r i n g prolonged s t i m u l a t i o n i s demonstrated . . 12 5 D u r a t i o n of impedance change e l i c i t e d by v a r i o u s continuous pure tone s t i m u l i - ( a ) and bands of white n o i s e ( b ) , i n t e n s i t y l e v e l 10 dB above the impedance t h r e s h o l d (1 s u b j e c t ) 25 6 Design of the experiment 30 7 Block diagram: Equipment f o r g e n e r a t i n g pure tones and n o i s e 33 8 Schematic diagram: Trace of impedance change d u r i n g a c o u s t i c s t i m u l a t i o n . . . 37 9 I n i t i a l s t r e n g t h of a c o u s t i c r e f l e x , as i n d i c a t e d by the s i z e of maximum pen d e f l e c t i o n i n the f i r s t 20 seconds of s t i m u l a t i o n , f o r each s u b j e c t i n Group I . 42 10 I n i t i a l s t r e n g t h of a c o u s t i c r e f l e x , as i n d i c a t e d by the s i z e of maximum pen d e f l e c t i o n i n the f i r s t 20 seconds of s t i m u l a t i o n , f o r each s u b j e c t i n Group I I . 43 11 Comparison of o r i g i n a l and r e t e s t v a l u e s of the i n i t i a l s t r e n g t h of a c o u s t i c r e f l e x f o r t h r e e c o n d i t i o n s f o r S u b j e c t s A and B . 46 12 R e f l e x decay, as i n d i c a t e d by the r a t i o of pen d e f l e c t i o n at 300 seconds t o maximum d e f l e c t i o n i n the f i r s t 20 seconds, f o r s u b j e c t s i n Group I 47 - v i i i -R e f l e x decay, as i n d i c a t e d by the r a t i o of pen d e f l e c t i o n at 3 0 0 seconds to maximum d e f l e c t i o n i n the f i r s t 2 0 seconds, f o r s u b j e c t s i n Group I I Muscle a c t i v i t y , as i n d i c a t e d by the r a t i o of pen d e f l e c t i o n a t time t seconds to maximum d e f l e c t i o n i n the f i r s t 2 0 seconds, as a f u n c t i o n of time f o r P T , T O B N , and O B N c o n d i t i o n s . Each p o i n t r e p r e s e n t s the mean value of the nine s u b j e c t s i n Group I . . . Muscle a c t i v i t y , as i n d i c a t e d by the r a t i o of pen d e f l e c t i o n a t time t seconds to maximum d e f l e c t i o n i n the f i r s t 2 0 seconds, as a f u n c t i o n of time f o r P T , T O B N , and O B N c o n d i t i o n s . Each p o i n t r e p r e s e n t s the mean value of the nine s u b j e c t s i n Group I I . . . i x -Acknowledgment I would l i k e to thank everyone who has had a p a r t i n t h i s t h e s i s , e s p e c i a l l y : Dr. John H. G i l b e r t , my s u p e r v i s o r and f r i e n d , f o r g i v i n g me the o p p o r t u n i t y to do my own r e s e a r c h and f o r guidance d u r i n g the w r i t i n g of my t h e s i s . Dr. A n d r e - P i e r r e Benguerel and 'Dr. Joyce D. .Edwards f o r s e r v i n g on my committee. Dr. R. P. Gannon f o r s e r v i n g on my committee and f o r p e r m i s s i o n to use the equipment i n the Audio-V e s t i b u l a r U nit at Vancouver General H o s p i t a l . My f r i e n d s who w i l l i n g l y served as s u b j e c t s . My f a m i l y f o r t h e i r support and encouragement throughout my graduate t r a i n i n g and f o r t h e i r thorough p r o o f r e a d i n g of my t h e s i s . My f e l l o w students who shared i n the experiences of the past two y e a r s . -x-Chapter 1 I n t r o d u c t i o n Sound i s an i n t e g r a l p a r t of the environment. A l l sounds, r e g a r d l e s s of o r i g i n , f o l l o w the same path through the a u d i t o r y - c e n t r a l nervous system. Sound waves, concentrated and d i r e c t e d i n t o the e x t e r n a l a u d i t o r y meatus by the e x t e r n a l ear, s t r i k e the tympanic membrane where the p r e s s u r e changes of sound waves are transformed i n t o mechanical v i b r a t i o n s . O s s i c l e s i n the middle ear conduct these v i b r a t i o n s from the tympanic membrane t o the c o c h l e a i n the i n n e r ear, i . e . , they e f f i c i e n t l y t r a n s m i t a c o u s t i c energy from the a i r - f i l l e d e x t e r n a l ear t o the f l u i d - f i l l e d i n n e r ear. I n the c o c h l e a , the mechanical energy of the v i b r a t i o n s i s e l e c t r o - c h e m i c a l l y transformed t o impulses which are t r a n s m i t t e d by the a u d i t o r y nerve and h i g h e r order neurons to the a u d i t o r y c o r t e x . I n a d d i t i o n t o the o s s i c l e s , the middle ear c o n t a i n s the two " s m a l l e s t s t r i a t e d muscles i n the body"(Zemlin, 1968, p. 382). The t e n s o r tympani muscle was d e s c r i b e d by E u s t a c h i u s i n 1564 and the s t a p e d i u s muscle was f i r s t a c c u r a t e l y d e s c r i b e d by V a r o l i u s i n 1591(cited i n Wever and Lawrence, 1954, p. 5)- Although the gross anatomy of these muscles was d e s c r i b e d i n the s i x t e e n t h century, attempts at d e s c r i b i n g t h e i r p h y s i o l o g y were not made u n t i l the t w e n t i e t h c e n t u r y . ; -2-The human m i d d l e e a r m u s c l e s c a n be s t u d i e d d i r e c t l y o n l y i n a b n o r m a l e a r s ; c o n s e q u e n t l y t h e r e p o r t e d number o f d i r e c t o b s e r v a t i o n s on m u s c l e p h y s i o l o g y a r e few. C e r t a i n a s p e c t s o f m i d d l e e a r m u s c l e a c t i v i t y h a v e , h o w e v e r , b e e n p r e s u m e d f r o m s t u d i e s p r i m a r i l y c o n c e r n e d w i t h t h e e f f e c t s o f h i g h i n t e n s i t y e x p o s u r e s on t h e e a r , a n d f r o m i n d i r e c t s t u d i e s o f t h e m u s c l e s u s i n g a c o u s t i c i m p e d a n c e m e a s u r e m e n t s and t y m p a n o m e t r y . Much o f t h e i n f o r m a t i o n g a t h e r e d f r o m t h e s e s t u d i e s h a s b e e n r e l a t e d t o d e t e r m i n a t i o n o f t h e t h r e s h o l d a n d l a t e n c y o f t h e a c o u s t i c r e f l e x , b u t n o t w i t h t h e a c t i v i t y o f t h e r e f l e x d u r i n g c o n t i n u o u s s t i m u l a t i o n . The o b j e c t i v e o f t h i s s t u d y was t o i n v e s t i g a t e a c t i v i t y o f t h e m i d d l e e a r m u s c l e s d u r i n g s t i m u l a t i o n w i t h p u r e t o n e s a n d n o i s e . . Chapter 2 Review o f the L i t e r a t u r e T h i s c h a p t e r w i l l d i s c u s s the middle ear muscles, the a c o u s t i c r e f l e x , and the l i t e r a t u r e r e l e v a n t t o the study o f m i d dle ear muscle a c t i v i t y d u r i n g a c o u s t i c s t i m u l a t i o n . M i d d l e E a r Muscles and A c o u s t i c R e f l e x The l a r g e r o f the two middle ear muscles i s the t e n s o r t y m p a n i ( F i g u r e 1). I t i s 25 m i l l i m e t e r s l o n g and has a c r o s s s e c t i o n a l a r e a o f 5*85 square m i l l i m e t e r s . The d i s t a l p a r t o f the muscle i s l o c a t e d i n the c o c h l e a r i f o r r a p r o c e s s , a bony s h e l f i n the middle e a r c a v i t y . I n man, o n l y the tendon o f the t e n s o r tympani e n t e r s the middle ear c a v i t y . The tendon i n s e r t s on the m e d i a l s i d e o f the manubrium n e a r the neck o f the mal l e u s ( K o b r a k , 1959). When the t e n s o r c o n t r a c t s , the m a l l e u s i s p u l l e d inward and f o r w a r d i n c r e a s i n g the t e n s i o n o f the tympanic membrane. The t e n s o r tympani i s i n n e r v a t e d by a branch o f the t r i g e m i n a l n e r v e . The s t a p e d i u s m u s c l e ( F i g u r e 2) i s 6.J m i l l i m e t e r s l o n g and has a c r o s s s e c t i o n a l a r e a o f 5 square m i l l i m e t e r s . L i k e the t e n s o r , the b e l l y o f the s t a p e d i u s muscle i s l o c a t e d i n a secondary c a v i t y i n the p o s t e r i o r w a l l of the middle e a r . The tendon of the s t a p e d i u s e n t e r s the middle ear c a v i t y and i n s e r t s on the head o f the s t a p e s near i t s a r t i c u l a t i o n w i t h the i n c u s . V/hen the s t a p e d i u s c o n t r a c t s , i t p u l l s the s t a p e s out of tha o v a l window i n an outward -4-F i g . 1. Schematic i l l u s t r a t i o n of the t e n s o r tympani muscle(from Zemlin, 1968, p. 383). Root Fie ot F i g . 2. Schematic of the stapedius muscle and the attachment of i t s tendon to the neck of the s t a p e s ( Z e m l i n , 1968, p. 384). - 5 -and downward d i r e c t i o n . The stapedius i s i n n e r v a t e d by a branch of the f a c i a l nerve. "The middle ear muscles are thou,ght to ' c o n t r i b u t e to the s t r e n g t h and r i g i d i t y of the o s s i c u l a r mechanism,' and to ' a s s i s t the suspensory ligaments i n m a i n t a i n i n g the o s s i c u l a r mechanism i n i t s proper p o s i t i o n and i n a s t a t e of t e n s i o n s u i t a b l e f o r the r e c e p t i o n o f sounds.' "(Galambos and Rupert, 1 9 5 9 , p. 3 5 1 ) , i . e . , the muscles form a f u n c t i o n a l u n i t . When the middle ear muscles c o n t r a c t , they i n c r e a s e the p u l l on the o s s i c u l a r c h a i n presumably s t i f f e n i n g the tympanic membrane and o s s i c l e s and changing the c o u p l i n g between the o s s i c l e s ( J e p s e n , 1 9 6 3 ) . As a consequence of these a c t i o n s , "the a c o u s t i c impedance of the eardrum i s changed but the r e l a t i v e p o s i t i o n of the eardrum i s probably u n a l t e r e d w i t h t o t a l r e f l e x a c t i v i t y because the two muscles appear to be a n t a g o n i s t i c to each o t h e r " ( K r y t e r , 1 9 7 0 , p. 96). The e f f i c i e n c y of sound t r a n s m i s s i o n through the middle ear i s t h e r e f o r e a l t e r e d when the middle ear muscles c o n t r a c t . " R e f l e x c o n t r a c t i o n of these muscles can be produced by ( i ) c l i c k s , tones and n o i s e s , ( i i ) i r r i t a t i o n of the e x t e r n a l meatus, p i n n a or face and ( i i i ) b o d i l y movements, e s p e c i a l l y swallowing and yawning."(Towe, 1 9 6 5 , p . 3 8 1 ) In man, i t i s thought t h a t o n l y the sta p e d i u s muscle i s i n v o l v e d i n the a c o u s t i c r e f l e x . When the stapedius i s i n o p e r a t i v e , e.g., from f a c i a l nsrve p a r a l y s i s , the r e f l e x i s e l i m i n a t e d ; when the t e n s o r i s i n o p e r a t i v e , there i s l i t t l e or no e f f e c t on the r e f l e x ( D j u p e s l a n d , 1965; K l o c k h o f f , 1961). The te n s o r i s thought to c o n t r a c t o n l y —o-when a c o u s t i c s t i m u l a t i o n produces g e n e r a l muscle c o n t r a c t i o n as i n a s t a r t l e r e a c t i o n ( D j u p e s l a n d , 1 9 6 5 ) . The r e f l e x a r c o f the s t a p e d i u s muscle has t h r e e d i v i s i o n s — a n a f f e r e n t and e f f e r e n t s e c t i o n , and r e f l e x c e n t e r ( F i g u r e 3 ) . The a f f e r e n t s e c t i o n o f the r e f l e x a r c i n v o l v e s the c o c h l e a and a u d i t o r y n e r v e . Axons from the s p i r a l g a n g l i o n , c e l l body o f the a u d i t o r y n e r v e , t e r m i n a t e i n the c o c h l e a r n u c l e i i n the m e d u l l a ( J e p s e n , 1 9 6 3 ) . From t h e s e n u c l e i , f i b r e s p r o c e e d t o the r e f l e x c e n t e r i n the pons, p r o b a b l y i n the s u p e r i o r o l i v a r y n u c l e i . F i b r e s p r o j e c t t o h o m o l a t e r a l and c o n t r a l a t e r a l o l i v a r y n u c l e i t h e r e f o r e u n i l a t e r a l a c o u s t i c s t i m u l a t i o n o f the e a r s r e s u l t s i n b i l a t e r a l c o n t r a c t i o n o f the muscles. " A n a t o m i c a l l y , the s u p e r i o r o l i v e l i e s immediately r o s t r a l t o the f a c i a l n u c l e u s , and a t one p o i n t i t s c e l l s i n t e r m i n g l e b r i e f l y w i t h t hose o f t h a t n u c l e u s " ( G a c e k , 1 9 7 2 , p. 247). The neurons c o n n e c t i n g the s u p e r i o r o l i v e w i t h the f a c i a l n u c l e u s are t h e r e f o r e s h o r t , but the c e l l b o d i e s o f the n e r v e s i n n e r v a t i n g the s t a p e d i u s muscle have not y e t been a c c u r a t e l y l o c a t e d w i t h i n the f a c i a l n u c l e u s . The e f f e r e n t s e c t i o n o f the r e f l e x a r c i n v o l v e s a branch o f the f a c i a l n e r v e . The s t a p e d i u s r e f l e x ( a c o u s t i c r e f l e x , a c o u s t i c s t a p e d i u s r e f l e x , or middle ear muscle r e f l e x ) i s e l i c i t e d by a c o u s t i c s t i m u l a t i o n o f s u f f i c i e n t i n t e n s i t y , g e n e r a l l y 60 to 90 dB SL. White n o i s e and narrowband n o i s e ( c e n t e r f r e q u e n c i e s 2000 and 4000 Ha) are a p p a r e n t l y more e f f e c t i v e i n A P i g . J . Diagram of presumed course of acoustic stapedius r e f l e x arc: A, cochlea; B, cochlear nerve; G, primary auditory centers; D, superior o l i v a r y nucleus; E, f a c i a l motor nucleus; E, f a c i a l nerve; G, stapedius muscle and stapes; H, chorda tympani; I, stylomastoid foramen; J, to temporal lobe(from Jepsen, 1963, p. 198). ~8-e l i c i t i n g the r e f l e x t han pure tones(2000 and 4000 Hz) s i n c e the t h r e s h o l d s a re 62 dB SL and 81 dB SL, r e s p e c t i v e l y (Deutsch, 1972). The l a t e n c y o f the a c o u s t i c r e f l e x has been s t u d i e d u s i n g v a r i o u s methods. Electromyography has shown t h a t a c t i o n p o t e n t i a l s appeared i n the s t a p e d i u s a p p r o x i m a t e l y 10 msec a f t e r i n t r o d u c t i o n o f a 1000 Hz tone a t 100 dB (Perlman and Cas-3, 1939). A c o u s t i c impedance measurements have shown the l a t e n c y was a p p r o x i m a t e l y 150 msec f o r a 1000 Hz tone p r e s e n t e d at t h r e s h o l d and 35 msec f o r the same tone p r e s e n t e d 30 t o 40 dB above t h r e s h o l d ( M e t z , 1951). The v a l u e s f o r the l a t e n c y d etermined by t h e s e two methods are not d i r e c t l y comparable because i t t a k e s time f o r muscle c o n t r a c t i o n t o a f f e c t t he impedance o f the e a r . The response o f the r e f l e x i n c r e a s e s i n d u r a t i o n and s t r e n g t h as the i n t e n s i t y o f the s t i m u l u s i s i n c r e a s e d . D u r i n g c o n t i n u o u s s t i m u l a t i o n , the muscles g r a d u a l l y r e l a x . Metz(1951) suggested t h a t the r e l a x a t i o n o f the muscles was not due to muscle f a t i g u e but to a d a p t a t i o n o f the e a r . V a r i o u s s t u d i e s ( G j a e v e n e s and So h o e l , 1966; Kobrak, L i n d s a y , and Perlman, 1941; K r y t e r , 1970) have shown (a) t h a t normal c o n t r a c t i o n s can be e l i c i t e d , w i t h no r e c o v e r y p e r i o d needed, onca the exposure ton-3 i s removed, (b) t h a t t h e r e i s l i t t l e or no r e l a x a t i o n o f the muscle w i t h i n t e r m i t t e n t s t i m u l i , and ( c ) t h a t normal c o n t r a c t i o n s can be produced a f t e r p r o l o n g e d s t i m u l a t i o n by changing the f r e q u e n c y o r i n t e n s i t y o f the s t i m u l u s . These r e s u l t s l e n d support t o -9-Metz's s u g g e s t i o n , s i n c e normal c o n t r a c t i o n s could not be produced i f the muscle was f a t i g u e d . M i l l e r ( 1 9 6 1 ) suggested t h a t middle ear muscle a c t i v i t y c o u l d be "considered as a p o s s i b l e i n d i c a t o r of a u d i t o r y n e u r a l a c t i v i t y at the l e v e l of the s u p e r i o r o l i v e " ( p . 1669). I f t h i s i s the case, r e l a x a t i o n of the muscle c o u l d r e f l e c t a d a p t a t i o n i n the nervous system up t o t h i s l e v e l i n the b r a i n stem. D i r e c t Observations of the Stapedius Muscle and Electromyography In 1929, Luscher observed c o n t r a c t i o n s of the stapedius muscle through a p e r f o r a t i o n i n the tympanic membrane. H i s ob s e r v a t i o n s showed t h a t the muscle d i d not remain c o n t r a c t e d f o r l o n g e r than 70 seconds when s t i m u l a t e d by a continuous sound(Perlman, 1938) and t h a t n o i s e s produced c o n t r a c t i o n of the muscle more e a s i l y than pure t o n e s ( P o t t e r , 1936). S i m i l a r o b s e r v a t i o n s of the stapedius muscle by Kobralc et al(1941) showed t h a t the muscle r e l a x e d d u r i n g continuous s t i m u l a t i o n , e.g., f i v e minutes w i t h a pure tone. The aut h o r s , however, d i d not give the c h a r a c t e r i s t i c s of the tone. During middle ear surgery on two p a t i e n t s , F i s c h and Schulthess(1963) recorded a c t i o n p o t e n t i a l s from the sta p e d i u s muscle i n response t o a c o u s t i c s t i m u l a t i o n . T h e i r r e s u l t s i n d i c a t e d t h a t the t h r e s h o l d of the stapedius r e f l e x was lower f o r masking n o i s e ( g e n e r a t e d by a Beoton audiometer) than f o r pure tones. S t a p e d i a l responses of l a r g e s t amplitude were recorded w i t h s t i m u l a t i o n by a 2000 H z tone - IVJ-and by masking n o i s e . S t a p e d i a l responses e l i c i t e d by a 4000 Hz tone were g r e a t e r i n amplitude than responses e l i c i t e d by tones of f r e q u e n c i e s below 1000 Hz. Extratympanic Manometry Using the e x t e r n a l a u d i t o r y c a n a l as a manometric tube, M e n d e l s o n ( 1 9 5 7 ) recorded p r e s s u r e changes(measured i n /iHg) i n the c a n a l d u r i n g s t i m u l a t i o n w i t h pure tones(400 Hz to 8000 Hz) presented at 80 to 1 1 5 dB 8PL. P r e s s u r e changes i n the c a n a l are caused by movement of the tympanic membrane i n response t o middle ear muscle c o n t r a c t i o n . Although the response p a t t e r n s ( o b t a i n e d by measuring changes i n a i r pressure i n the e x t e r n a l c a n a l of h i s s u b j e c t s ) v a r i e d q u a n t i t a t i v e l y , Mendelson noted some i n t e r e s t i n g q u a l i t a t i v e d i f f e r e n c e s . In the measured responses from some s u b j e c t s , pressure p l a t e a u s , i . e . , p e r i o d s when the pressure change remained a t a constant l e v e l above b a s e l i n e , were maintained f o r the d u r a t i o n of the s t i m u l u s ; however, f o r the m a j o r i t y , the pressure " r e t u r n e d to the base l i n e before the end of s t i m u l a t i o n " (p. 5 0 1 ) . Eor some s u b j e c t s , the c h a r a c t e r i s t i c response was a sharp, s p i k e - l i k e c o n t r a c t i o n which r e t u r n e d to the b a s e l i n e or l e v e l l e d o f f at a reduced p r e s s u r e . Mendelson d e s c r i b e d the v a r i o u s response p a t t e r n s but d i d not r e p o r t responses to s t i m u l i of s p e c i f i c f r e q u e n c i e s , i n t e n s i t i e s or d u r a t i o n . H o i s t , I n g e l s t e d t , and C r t e g r e n ( 1 9 6 3 ) a l s o s t u d i e d the movements of the tympanic membrane by m o n i t o r i n g pressure - 1 1 -changes i n the e x t e r n a l a u d i t o r y c a n a l . These a u t h o r s i n d i c a t e d t h a t e a r l i e r r e s e a r c h had shown " t h a t the r e f l e x c o n t r a c t i o n f o l l o w i n g a c o u s t i c s t i m u l a t i o n does not remain i f the s t i m u l u s sound i s m a i n t a i n e d f o r a l o n g i s h t i m e — a f t e r about 30-60 seconds the muscles r e l a x a g a i n " ( p . 8 0 ) . H o i s t e t a l r e p o r t e d t h a t t h e i r o b s e r v a t i o n s f o r s t i m u l a t i o n w i t h pure tones agreed w i t h t h e s e f i n d i n g s . F i g u r e 4 r e p r e s e n t s the o n l y d a t a i n the H o i s t et a l paper concerned w i t h changes i n the movement o f the tympanic membrane w i t h t i m e . The r e s u l t s shown i n t h i s f i g u r e do not agree w i t h t h ose o f the s t u d i e s the a u t h o r s d i s c u s s e d . The muscles must have r e l a x e d b e f o r e c o n c l u s i o n o f the 30 t o 60 second i n t e r v a l p r e v i o u s l y r e p o r t e d s i n c e tympanic membrane movement d e c r e a s e d t o l e s s t h a n h a l f the i n i t i a l l e v e l a f t e r o n l y t h r e e and a q u a r t e r seconds o f s t i m u l a t i o n . E q u a l Loudness Experiments In 1938, Perlman d i s c u s s e d h y p e r a c u s i s ( i . e . , "abnormally acute sense o f h e a r i n g " ( J e p s e n , 1963, p. 226)) i n a p a t i e n t w i t h r i g h t f a c i a l nerve p a r a l y s i s . The p a t i e n t r e p o r t e d t h a t a 1000 Hz pure tone "seemed t o ' s t r i k e h i s r i g h t e ar f i r s t 1 and was d i s t i n c t l y l o u d e r i n t h a t e ar f o r about 4-5 seconds a f t e r which time, as the sounds c o n t i n u e d , he c o u l d determine no d i f f e r e n c e i n loudness between h i s e a r s . " ( P e r l m a n , 1938, p. 951) The sound was i n i t i a l l y l o u d e r i n the r i g h t e ar, presumably due i n p a r t to the i n o p e r a t i v e middle ear muscle. S i n c e the sound appeared e q u a l l y l o u d a f t e r 45 seconds, Perlman assumed t h a t a d a p t a t i o n o c c u r r e d i n the c e n t r a l nervous : I 1 SEC F i g . 4. Outward drum movement caused by acoustic . s t i m u l a t i o n . Muscle r e l a x a t i o n during prolonged s t i m u l a t i o n i s demonstrated. M=meatal recording, S=pure tone stimulation(from Hoist et a l , 19&3* P- 81). system and produced r e l a x a t i o n o f the s t a p e d i u s muscle on the l e f t s i d e . The muscle i n the l e f t e a r t h e r e f o r e remained c o n t r a c t e d f o r o n l y 45 seconds. C o n t r a l a t e r a l Ramote Masking(CRM) CRM produced by pure t o n e s and n o i s e . C o n t r a l a t e r a l remote masking may be d e f i n e d as "the change i n t h r e s h o l d i n one ear upon p r e s e n t a t i o n o f an a r o u s a l tone o r n o i s e to the c o n t r a l a t e r a l ear"(Ward, 1961, p. 1055). In 1961, Ward assumed t h a t the a u d i t o r y r e f l e x was r e s p o n s i b l e f o r most, i f n ot a l l , changes i n h e a r i n g t h r e s h o l d d u r i n g CRM. H i s experiments a t t h a t time showed t h a t CRM a t 250 Hz was l a r g e r f o r s t i m u l a t i o n w i t h low f r e q u e n c y n o i s e t h a n f o r s t i m u l a t i o n w i t h h i g h f r e q u e n c y n o i s e when the y were b o t h p r e s e n t e d a t 125 dB SPL. These r e s u l t s would i n d i c a t e " t h a t a low-f r e q u e n c y n o i s e i s more e f f i c i e n t t h an a h i g h - f r e q u e n c y n o i s e i n a r o u s i n g a s u s t a i n e d a c o u s t i c r e f l e x " ( W a r d , 1961, p. 1042). A l s o s t i m u l a t i o n w i t h narrowband n o i s e produced more CRM than s t i m u l a t i o n w i t h octave bands o f n o i s e . A 5400 Hz pure tone, p r e s e n t e d a t 120 dB SPL, produced no masking e f f e c t ; c o n s e q u e n t l y Ward propo s e d t h a t "Pure tones are a p p a r e n t l y not capable o f i n d u c i n g s u s t a i n e d r e f l e x a c t i v i t y , even at v e r y h i g h l e v e l s " ( p . 1044). Ward a l s o s t u d i e d the a d a p t a t i o n of CRM. The a d a p t a t i o n curves f o r v a r i o u s n o i s e s were l i n e a r f o r the f i r s t two minutes, but l e v e l l e d o f f w i t h c o n t i n u e d exposure. S i n c e CRM d e c r e a s e d w i t h time, Ward assumed t h a t the middle ear muscle adapted and "by about 3 min the r e f l e x a c t i v i t y has r e a c h e d a steady - I n -s t a t e " (p. 1040). F l e t c h e r and Loeb(1962) s t u d i e d the e f f e c t o f ste a d y and changing sounds o f h i g h f r e q u e n c y on the t h r e s h o l d o f a 500 Hz pure t o n e . T h e i r r e s u l t s showed t h a t narrow band n o i s e ( c u t o f f f r e q u e n c i e s 2000 and 2200 Hz) and broad band n o i s e ( l o w e r c u t o f f 2000 Hz) produced a l a r g e r s h i f t i n the t h r e s h o l d o f the tone than a 2200 Hz pure tone or 2200 Hz square wave, when a l l maskers were p r e s e n t e d a t 110 dB 3L. D u r i n g the exposure, the r e d u c t i o n i n CRM 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 f o r the pure tone, square wave, and broad band n o i s e but was not s t a t i s t i c a l l y s i g n i f i c a n t f o r narrow band n o i s e . The a u t h o r s i n f e r r e d from t h e s e r e s u l t s t h a t "narrow band n o i s e was a p p a r e n t l y more e f f e c t i v e n ot o n l y i n amount of a t t e n u a t i o n p r o v i d e d , but a l s o i n m a i n t a i n i n g the c o n t r a c t i o n " ( F l e t c h e r and Loeb, 1962, p. 35) and t h a t broad band n o i s e was more e f f e c t i v e t han a pure tone o r square wave. T h e i r r e s u l t s f o r narrow band and broad band n o i s e s l e n d support t o the f i n d i n g s o f Ward(1961) t h a t narrow band n o i s e produces more CRM t h a n broad band n o i s e and pure t o n e s . CRM and middle ear muscle a c t i v i t y . A c c o r d i n g t o Ward(1963) c e n t r a l masking, c o n t r a c t i o n o f the middle ear muscles, and d i s t o r t i o n p r o d u c t s are p o s s i b l e s o u r ces f o r the i n c r e a s e i n t h r e s h o l d o f a sound d u r i n g CRM. However, i t has been d i f f i c u l t t o determine the i n d i v i d u a l c o n t r i b u t i o n s o f t h e s e f a c t o r s . As i n d i c a t e d p r e v i o u s l y , Ward(1961) showed t h a t masking e f f e c t s d e c r e a s e w i t h time; he assumed t h a t t h i s d e c r e a s e "must be due to the a c o u s t i c r e f l e x , s i n c e i t was -a l r e a d y known Cfrom animal s t u d i e s ] t h a t the muscles g r a d u a l l y r e l a x even under s u s t a i n e d a u d i t o r y s t i m u l a t i o n " (Ward, 1963, p. 2 4 8 ) . L a t e r , Ward(1963) i n d i c a t e d t h a t t h e r e was no r e a s o n why CRM c o u l d not d e c r e a s e w i t h time, independent of r e f l e x a d a p t a t i o n " j u s t as the judged l o u d n e s s o f the masker d o e s " ( p . 248). Smith, Loeb, F l e t c h e r , and Thomas(1966) s t u d i e d the r o l e o f the middle ear muscles i n CRM. They measured CRM produced by a h i g h f r e q u e n c y tone and by o c t a v e band n o i s e b e f o r e and a f t e r the a p p l i c a t i o n of d - t u b o c u r a r i n e ( u s e d to i n h i b i t the a c o u s t i c r e f l e x ) . CRM produced by tone and n o i s e was not s i g n i f i c a n t l y changed f o l l o w i n g a b s o r p t i o n o f the d r u g . These r e s u l t s would appear t o i n d i c a t e t h a t the a c o u s t i c r e f l e x i s not s i g n i f i c a n t l y i n v o l v e d i n CRM. In 1967? Ward d i s c u s s e d a number o f h i s own experiments and the experiments of o t h e r s which showed t h a t the middle e a r muscles are o n l y m i n i m a l l y i n v o l v e d i n CRM. D i f f e r e n c e s i n CRM produced by v a r i o u s s t i m u l i can t h e r e f o r e no l o n g e r be assumed to be caused s o l e l y by d i f f e r e n c e s i n the a c t i v i t y o f the middle e a r muscles. Temporary T h r e s h o l d S h i f t ( T T 3 ) TTS produced by exposure to n o i s e . " T h r e s h o l d s h i f t i s the d e c r e a s e i n a u d i t o r y a c u i t y which f o l l o w s exposure to loud n o i s e " ( F l e t c h e r , 1962, p. 1 8 ) . Experiments by Ward, G l o r i g , and Sklar ( 1 9 5 9 ) and Ward(1962 a) showed t h a t low f r e q u e n c y octave band n o i s e produced l e s s TTS than h i g h f r e q u e n c y octave band n o i s e , when they were p r e s e n t e d at the — i D -same i n t e n s i t y . Based on the r e s u l t s of CRM experiments, Ward assumed these d i f f e r e n c e s were due t o the f a c t t h a t c o n t r a c t i o n of the s t a p ed i u s attenuates low f r e q u e n c i e s more than h i g h f r e q u e n c i e s and t h a t "low-frequency n o i s e produces a s t r o n g e r c o n t r a c t i o n than high-frequency n o i s e " (Ward, 1962;a, p.257)-In order t o a s c e r t a i n the r o l e of the a c o u s t i c r e f l e x i n t h r e s h o l d s h i f t , Smith et al(1966) measured TTS "before and a f t e r a p p l i c a t i o n of d - t u b o c u r a r i n e . Smith et a l found t h a t TT3 from exposure to a 600-1200 Hz n o i s e was s i g n i f i c a n t l y l a r g e r f o l l o w i n g a b s o r p t i o n of the drug, but was not s i g n i f i c a n t l y changed f o r a 24-00-4800 Hz n o i s e . These r e s u l t s l e n d support t o Ward's assumption t h a t low frequency n o i s e i s a t t e n u a t e d more than h i g h frequency n o i s e by a c t i v a t i o n of the a c o u s t i c r e f l e x . TTS produced by pure tones and n o i s e . F l e t c h e r ( 1 9 6 1 ) wished t o determine which s t i m u l i , pure t o n e s , narrow band noise(NBN), and c l i c k s , were most e f f e c t i v e i n e l i c i t i n g the a c o u s t i c r e f l e x and would t h e r e f o r e reduce the f a t i g u i n g e f f e c t s of white n o i s e the most. He found t h a t TTS produced by white n o i s e was the same whether or not tones were presented to the n o n - f a t i g u e d ear. TTS was s i g n i f i c a n t l y reduced, however, when NBN or c l i c k s were presented to the n o n - f a t i g u e d ear. F l e t c h e r suggested t h a t the a c t i v i t y of the a c o u s t i c r e f l e x was r e s p o n s i b l e f o r these r e s u l t s ; he concluded t h a t s t i m u l a t i o n by NBN and c l i c k s maintained c o n t r a c t i o n of the muscles longer than - I ( -s t i m u l a t i o n by pure tones. Subsequent experiments by Ward(1962 b, 1966) demonstrated: (a) t h a t a 7 0 0 Hz pure tone produced more TTS than NBN, centered at 7 0 0 Hz, when both were presented at 1 2 5 dB SPL f o r f i v e minutes; (b) t h a t TTS a f t e r s t i m u l a t i o n w i t h an 850 Hz tone was the same or g r e a t e r than a f t e r s t i m u l a t i o n w i t h a 600-1200 Hz n o i s e ; (c) t h a t a 1 7 0 0 Hz tone produced more TTS at 2000 and 3 0 0 0 Hz than a 1200-2400 Hz n o i s e , but the same TTS at 1500, 4000, and 6000 Hz; and (d) t h a t a 3^-00 Hz pure tone and v a r i o u s h i g h frequency octave band n o i s e s produced almost the same maximum TTS. Using the same r a t i o n a l e as i n h i s p r e v i o u s experiments and based on CRM d a t a , Ward(1962 b) hypothesized t h a t the a c t i v i t y of the middle ear muscles, i n response t o s t i m u l a t i o n , c o u l d account f o r h i s r e s u l t s . In order to t e s t t h i s h y p o t h e s i s , Ward s t u d i e d the e f f e c t of n o i s e ( p r e s e n t e d t o the n o n - f a t i g u e d ear and used to e l i c i t the a c o u s t i c r e f l e x ) on TTS produced by exposure t o pure tones. He found t h a t NBN, centered at 7 0 0 Hz, reduced the f a t i g u i n g e f f e c t s of a 7 0 0 Hz pure tone; but NBN, centered at 2000 Hz, had no e f f e c t on TTS produced by a 2 0 0 0 Hz tone. The former r e s u l t s agree w i t h those of F l e t c h e r ( 1 9 6 1 ) . F l e t c h e r and Ward, however, e r r e d i n the i n t e r p r e t a t i o n of t h e i r e xperimental r e s u l t s by assuming t h a t z^eflex a c t i v i t y of the middle ear muscles was e x c l u s i v e l y r e s p o n s i b l e . The muscles may have p l a y e d only a minor role(compare w i t h CRM). I t i s p o s s i b l e — I o — t h a t NBN and c l i c k s might have i n t e r a c t e d w i t h the white n o i s e and pure tones at a h i g h e r l e v e l i n the c e n t r a l nervous system i n such a way as t o reduce t h e i r f a t i g u i n g e f f e c t s . I n o t h e r words, although i t might be t r u e t h a t d i f f e r e n c e s i n TTS produced by tones and n o i s e are due t o middle ear muscle a c t i v i t y , the procedure F l e t c h e r and Ward used d i d not t e s t the h y p o t h e s i s . Assuming t h a t the middle ear muscles were r e s p o n s i b l e f o r low frequency n o i s e p r o d u c i n g l e s s TTS than pure tones, M i l l s and Lilly(1971) hypothesized t h a t TTS would be the same i f the s t a p e d i u s muscle was i n o p e r a t i v e . They t e s t e d t h i s n o t i o n by comparing TTS i n s u b j e c t s who had normal middle ears or had had stapedectomies. Using a 710 Hz pure tone and a one-eighth octave band noise(upper c u t o f f 710 Hz), M i l l s and L i l l y found, as expected, t h a t n o i s e and tone produced the same amount of TTS i n the stapedectomized group. TTS and middle ear muscle a c t i v i t y . F l e er(1962) found t h a t v o l u n t a r y c o n t r a c t i o n of the s t a p e d i u s muscle before a s e r i e s of i m p u l s i v e sounds reduced the amount of of T T S ( c i t e d i n Loeb and F l e t c h e r , 1963). M i l l s and L i l l y (1971) showed t h a t TTS produced by tones and n o i s e was s i m i l a r when the stapedius was i n o p e r a t i v e . These s t u d i e s demonstrated t h a t TTS i s a f f e c t e d . b y middle ear muscle a c t i v i t y , but muscle a c t i v i t y was not normal. S e v e r a l i n v e s t i g a t o r s have attempted to determine r e l a t i o n s h i p s between d i f f e r e n t measures of normal, i n v o l u n t a r y muscle a c t i v i t y and amount o f TTS. "In g e n e r a l , i t seems r e a s o n a b l e t h a t t h o s e s u b j e c t s showing the g r e a t e s t r e f l e x a c t i v a t i o n s h o u l d show the l e a s t TTS"(Ward, 1961, p. 1043). However, Ward(1961) found no s i g n i f i c a n t c o r r e l a t i o n between TTS and the degree o f muscle a c t i v a t i o n . B r a s h e r , C o l e s , Elwood, and Ferres(1970) a l s o found no s i g n i f i c a n t c o r r e l a t i o n s between TTS and a c o u s t i c r e f l e x t h r e s h o l d , or betv/een TTS and a b s o l u t e v a l u e s o f i n i t i a l s t r e n g t h o f the r e f l e x and r e s i d u a l s t r e n g t h a f t e r two minutes o f s t i m u l a t i o n . U s i n g r a n k - o r d e r c o r r e l a t i o n between TTS and the r a t i o o f f i n a l impedance t o i n i t i a l impedance, McBay(1971) found the c o r r e l a t i o n was n e g a t i v e and f a i r l y h i g h but not s t a t i s t i c a l l y s i g n i f i c a n t . Lack o f s i g n i f i c a n t c o r r e l a t i o n s between v a r i o u s measures o f middle ear. muscle a c t i v i t y and TTS i s d i f f i c u l t t o e x p l a i n i f r e f l e x a c t i v i t y i n f l u e n c e s TTS as has p r e v i o u s l y been assumed. T h i s l a c k o f c o r r e l a t i o n may, however, be because the measures used were not the b e s t w i t h which to demonstrate a r e l a t i o n s h i p . At t h i s time, i t may be wise to r e f r a i n from drawing d e f i n i t i v e c o n c l u s i o n s about middle ear muscle a c t i v i t y based on r e s u l t s of TTS experiments, a t l e a s t u n t i l the r e l a t i o n s h i p between them i s more f u l l y u n d e r s t o o d . A c o u s t i c Impedance Measurements When the middle ear muscles c o n t r a c t i n response to a c o u s t i c s t i m u l a t i o n , the impedance of the e a r ( a measure of the system's o p p o s i t i o n t o movement) i s i n c r e a s e d . -20-Recording changes i n the ear's impedance d u r i n g a c o u s t i c s t i m u l a t i o n w i l l t h e r e f o r e i n d i r e c t l y r e f l e c t responses of the middle ear muscles. Impedance changes e l i c i t e d by pure tones. Using a mechanical a c o u s t i c impedance b r i d g e to r e c o r d impedance changes, Metz(1951) s t u d i e d responses of the middle ear muscles to s t i m u l a t i o n by a 1000 Hz pure tone at 100 dB. Con f i r m i n g e a r l i e r o b s e r v a t i o n s of Mendelson, Metz found v a r i a b i l i t y i n responses of d i f f e r e n t s u b j e c t s . For some s u b j e c t s , the impedance remained at a constant l e v e l ( i . e . , the muscles remained c o n t r a c t e d ) f o r many seconds once the change i n impedance had reached i t s maximum; f o r other s u b j e c t s , the impedance decreased r a p i d l y . Metz assumed decreases i n impedance d u r i n g prolonged s t i m u l a t i o n were due to a d a p t a t i o n not t o muscle f a t i g u e . I n 1958, M i l l e r s t u d i e d the c o n t r a c t i o n of the muscles e l i c i t e d by pure t o n e s . Data from t h i s study i n d i c a t e t h a t the muscles remained f u l l y c o n t r a c t e d f o r the d u r a t i o n of the s t i m u l u s , approximately one and a h a l f seconds. Gjaevenes and 36hoel(1966) showed t h a t s t i m u l a t i o n w i t h a 1000 Hz pure tone, presented 10 dB above r e f l e x t h r e s h o l d , produced impedance changes w i t h g r a d u a l l y decreased. A f t e r 60 seconds of s t i m u l a t i o n , the impedance reached a s t a b l e l e v e l . The authors d i d not r e c o r d impedance changes longer than 60 seconds; consequently i t i s not known f o r how long the impedance would have remained at the s t a t i o n a r y l e v e l . Johansson, K y l i n , and Langfy(1967) compared the d u r a t i o n o f impedance changes e l i c i t e d by low and h i g h f r e q u e n c y pure t o n e s p r e s e n t e d a t 120 dB SPL f o r 15 t o 20 seconds. With 500 Hz, the impedance c h a n g e ( i . e . , the muscle r e s p o n s e ) remained at maximum l e v e l f o r the d u r a t i o n o f s t i m u l a t i o n . With 2000 and 3 0 0 0 Hz, muscle response was reduced a f t e r 10 seconds to 5 0 $ and 8 3 $ i r e s p e c t i v e l y , o f maximum r e s p o n s e . Experiments by T i e t z e ( 1 9 6 9 ) l e n d support t o t h e s e f i n d i n g s . He found t h a t the impedance was reduced t o h a l f the maximum v a l u e a f t e r s t i m u l a t i o n w i t h 1 5 0 0 Hz f o r 10 seconds and a f t e r s t i m u l a t i o n w i t h 4000 Hz f o r 0.7 t o 20 seconds. With s t i m u l i o f 5 0 0 and 1000 Hz, impedance changes were m a i n t a i n e d f o r l o n g e r than 20 seconds. R e s u l t s o b t a i n e d a t 1000 Hz do not support the f i n d i n g o f Gjae venes and S o h o e l who r e p o r t e d the impedance g r a d u a l l y d e c r e a s e d a f t e r onset o f s t i m u l a t i o n . M c B a y ( 1 9 7 1 ) monitored impedance changes d u r i n g s t i m u l a t i o n w i t h a 5 0 0 Hz pure tone a t T18 dB SPL. Impedance was maximum 5 t o 20 seconds a f t e r p r e s e n t a t i o n o f the to n e . A f t e r f i v e minutes, the impedance had d e c r e a s e d , on average, t o 60% o f the v a l u e o f the impedance a t 1 5 seconds. There was, however, l a r g e i n t e r s u b j e c t v a r i a b i l i t y , f o r the s i x s u b j e c t s , the impedance at f i v e minutes ranged from 27/» t o 86$ o f the impedance at 1 5 seconds. I t would appear from the above s t u d i e s t h a t the a c t i v i t y o f the middle e a r muscles does not dec r e a s e when s t i m u l a t e d by low f r e q u e n c y t o n e s ( i . e . , ' t h o s e l e s s t h an 1000 Hz) f o r 2 0 seconds but does decrease when s t i m u l a t e d by h i g h frequency tones. When s t i m u l i are presented f o r longer than 20 seconds muscle a c t i v i t y a l s o decreases f o r low frequency tones. Impedance changes e l i c i t e d by n o i s e . In 1964, D a l l o s s t u d i e d the dynamic c h a r a c t e r i s t i c s of the a c o u s t i c r e f l e x . He used random noise(90-2800 Hz) at v a r i o u s i n t e n s i t i e s t o e l i c i t the r e f l e x . Although t h e r e was l a r g e v a r i a b i l i t y i n the amount and r a t e of a d a p t a t i o n , a s i m i l a r response p a t t e r n was demonstrated f o r a l l s i x s u b j e c t s . At h i g h s t i m u l u s i n t e n s i t i e s ( 1 0 7 and 112 dB 3PL), t h e r e was s u s t a i n e d c o n t r a c t i o n of the muscles; at lower i n t e n s i t i e s , t h e r e was a steady d e c l i n e i n the degree of c o n t r a c t i o n a f t e r an i n i t i a l peak response. D a l l o s found " t h a t the g r e a t e s t degree of a d a p t a t i o n occurs i n the immediate 20-30 sec a f t e r onset of the response"(p. 2181) and t h a t muscle response, when there was a d a p t a t i o n , decreased c o n t i n u o u s l y d u r i n g s t i m u l a t i o n l a s t i n g one and a h a l f t o two minutes. T h i s r e s u l t does not support the o b s e r v a t i o n of Gjaevenes and Sohoel(1966) t h a t muscle response reaches a s t a t i o n a r y l e v e l a f t e r one minute of s t i m u l a t i o n w i t h a 1000 Hz tone. D a l l o s ' s study showed th e r e was no a d a p t a t i o n f o r h i g h i n t e n s i t y random n o i s e w i t h d u r a t i o n s of two minutes. L i l l y ( 1 9 6 4 ) extended t h i s v a l u e . He r e p o r t e d t h a t the a c o u s t i c r e f l e x , e l i c i t e d by white n o i s e at h i g h i n t e n s i t y , c o u l d be maintained f o r 10 minutes. He d i d not, however, d e s c r i b e d e t a i l s of the study. Feldman and Z w i s l o c k i ( 1 9 6 5 ) noted t h a t a d a p t a t i o n of the a c o u s t i c r e f l e x ( e l i c i t e d by n o i s e ) was not s i g n i f i c a n t f o r i n t e n s i t i e s above 90 dB SPL f o r a p e r i o d of 10 seconds, which was the time necessary to rebalance the Z w i s l o c k i a c o u s t i c b r i d g e . Brasher et al(1970) compared the responses of the middle ear muscles t o s t i m u l a t i o n w i t h 1000 Hz and 4-000 Hz octave band n o i s e s , presented at 105 dB SPL f o r two minutes. T h e i r study confirmed f i n d i n g s of p r e v i o u s i n v e s t i g a t i o n s , i . e . , t h a t muscle responses adapt more s l o w l y f o r low frequency n o i s e than h i g h frequency n o i s e . A f t e r two minutes of s t i m u l a t i o n w i t h a 1000 Hz n o i s e , muscle responses were reduced to 0.6 of the i n i t i a l response and w i t h a 4000 Hz n o i s e , were reduced to 0.2 of the i n i t i a l response. As noted by D a l l o s ( 1 9 6 4 ) , most of the a d a p t a t i o n occurred d u r i n g the f i r s t 20 t o 30 seconds of s t i m u l a t i o n . Octave band n o i s e s t h e r e f o r e appear to f o l l o w the p a t t e r n shown f o r pure tones, i . e . , muscle responses adapt l e s s f o r low frequency s t i m u l i than f o r h i g h frequency s t i m u l i . I t i s d i f f i c u l t t o compare the a d a p t a t i o n of the muscles when s t i m u l a t e d by pure tones and n o i s e because the frequency, i n t e n s i t y or d u r a t i o n of the s t i m u l i used v a r i e d from one study t o another. Impedance changes e l i c i t e d by pure tones and n o i s e s Djupesland, F l o t t o r p , and Winther(1966) were concerned w i t h s t u d y i n g the d u r a t i o n of impedance changes i n r e l a t i o n to the frequency and i n t e n s i t y of pure tones and n o i s e . With a 250 Hz pure tone, the impedance change d i d not decrease s u b s t a n t i a l l y a f t e r two to t h r e e minutes of s t i m u l a t i o n ; but w i t h s t i m u l i of 1 0 0 0 , 2 0 0 0 , and 4000 Hz, the impedance began t o decrease immediately a f t e r onset of s t i m u l a t i o n ( P i g u r e 5 a A d a p t a t i o n was f a s t e s t f o r s t i m u l a t i o n w i t h a 4000 Hz tone. These r e s u l t s l e n d support t o the f i n d i n g s of Gj aevenes and Sbhoel(1966), Johansson et a l ( 1 9 6 7 ) , and T i e t z e ( 1 9 6 9 ) . The r e s u l t s f o r s t i m u l a t i o n w i t h white n o i s e ( F i g u r e 5'b) agre w i t h those of D a l l o s ( 1 9 6 4 ) who found muscle responses g r a d u a l l y decreased d u r i n g prolonged s t i m u l a t i o n . Djupesland et a l a l s o compared the d u r a t i o n of impedance changes f o r v a r i o u s pure tones and n o i s e i n t h r e e s u b j e c t s . Impedance changes f o r two • s u b j e c t s la&ted l o n g e r w i t h s t i m u l a t i o n by a low frequency pure t o n e s ( 2 5 0 and 5 0 0 Hz) than w i t h s t i m u l a t i o n by h i g h frequency t o n e s ( 5 0 0 0 and 4000 Hz); a s i m i l a r response p a t t e r n was found f o r one of these s u b j e c t s f o r s t i m u l a t i o n w i t h octave band n o i s e s . For the t h i r d s u b j e c t , impedance changes l a s t e d more than three minutes r e g a r d l e s s of the s t i m u l u s . For two s u b j e c t s , the middle ear muscles showed a tendency to adapt l e s s ( i . e . , the d u r a t i o n of the impedance change was l o n g e r ) w i t h i n c r e a s e d s t i m u l u s i n t e n s i t y . T h i s r e s u l t confirms the f i n d i n g s of D a l l o s ( 1 9 6 4 ) . Although o n l y a p p l i c a b l e f o r some s u b j e c t s , i t would appear t h a t impedance changes e l i c i t e d by octave band n o i s e s g e n e r a l l y l a s t l o nger than impedance changes e l i c i t e d by pure tones. F i g u r e 5 i l l u s t r a t e s t h i s tendency f o r one s u b j e c t . Using s t i m u l u s d u r a t i o n s of 10 and 50 seconds, M i l l s and L i l l y ( 1 9 6 9 ) found there was no d i f f e r e n c e "between the P i g . 5 a . JO 60 9 0 \io \«c F i g . .5 b . F i g . 5. D u r a t i o n o f i m p e d a n c e c h a n g e e l i c i t e d b y v a r i o u s c o n t i n u o u s p u r e t o n e s t i m u l i ( a ) a n d b a n d s o f w h i t e n o i s e ( b ) , i n t e n s i t y l e v e l 10 dB a b o v e t h e i m p e d a n c e t h r e s h o l d (1 s u b j e c t ) ( f r o m D j u p e s l a n d e t a l , 1966, P. 225). -26-pure tone[710 Hz] and the n o i s e [eighth octave' band] i n m a i n t a i n i n g a c t i v i t y of the a c o u s t i c r e f l e x " ( p . 80). D e t a i l s of the study were not r e p o r t e d . S i z e of e l i c i t e d impedance changes. The s i z e of impedance changes d u r i n g a c o u s t i c s t i m u l a t i o n v/as s t u d i e d by Djupesland et a l ( 1 9 6 6 ) . With i n c r e a s e d i n t e n s i t y , the s i z e of impedance changes i n c r e a s e d , although t h i s i n c r e a s e i n s i z e was l e s s f o r a 4000 Hz pure tone than f o r a 250 Hz tone. At the same i n t e n s i t y above r e f l e x t h r e s h o l d , the s i z e of the impedance change f o r a 250 Hz tone was some-what l a r g e r than f o r a 1000 Hz tone and much l a r g e r than f o r a 4000 Hz tone. Djupesland et a l give the f o l l o w i n g impedance changes f o r 16 dB above r e f l e x t h r e s h o l d : (a) f o r a 250 Hz tone—100$ of the maximum impedance change; (b) f o r a 1000 Hz t o n e — 8 0 $ of the maximum impedance change; and (c) f o r a 4000 Hz tone—50$ of the maximum impedance change. The maximum impedance changes f o r these pure tones were about the same, although the maxima occurred at d i f f e r e n t i n t e n s i t i e s . On the other hand, Brasher et al(1970) showed t h a t the average s i z e of the a c o u s t i c r e f l e x e l i c i t e d by a 1000 Hz octave band n o i s e , presented at 105 dB SPL, was s l i g h t l y s m a l l e r than t h a t e l i c i t e d by a 4000 Hz octave band n o i s e , presented at the same i n t e n s i t y . The d i f f e r e n t r e s u l t s f o r the two experiments may be due e i t h e r to the nature of the s t i m u l i used or to the use of SL by Djupesland et a l versus SPL by Brasher et a l . Chapter 3 Statement of the Problem The p r e c e d i n g l i t e r a t u r e review has shown t h a t the middle ear muscles may respond d i f f e r e n t l y when exposed to d i f f e r e n t a c o u s t i c s t i m u l i . One of the most d i r e c t s t u d i e s of muscle a c t i v i t y i n d i c a t e d t h a t the muscles do not remain c o n t r a c t e d f o r l o n g e r than 70 seconds w i t h continuous s t i m u l a t i o n ; another study i n d i c a t e d the muscles s l o w l y r e l a x e d w i t h s t i m u l a t i o n l a s t i n g f i v e minutes. These s t u d i e s a l s o demonstrated t h a t c o n t r a c t i o n s of the muscles are produced more e a s i l y by noise.;; than by tones. Experiments i n c o n t r a l a t e r a l remote masking and temporary t h r e s h o l d s h i f t have demonstrated t h a t n o i s e s produce more CRM and l e s s TTS than pure tones, and t h a t low frequency s t i m u l i produce more CRM and l e s s TTS than h i g h frequency s t i m u l i . Recent r e s e a r c h , however, has i n d i c a t e d t h a t the middle ear muscles are only m i n i m a l l y i n v o l v e d i n CRM; and the l i t e r a t u r e review has shown t h a t i t may be u n r e a l i s t i c to assume t h a t the muscles are e n t i r e l y r e s p o n s i b l e f o r TTS r e s u l t s . In other words, although c o n s i s t e n t r e s u l t s were ob t a i n e d from CRM and TTS i n v e s t i g a t i o n s these r e s u l t s may not r e f l e c t middle ear muscle a c t i v i t y . Measurement of pressure changes i n the e x t e r n a l a u d i t o r y c a n a l , and of changes i n a c o u s t i c impedance would appear t o be b e t t e r i n d i c a t o r s of middle ear muscle a c t i v i t y s i n c e c o n t r a c t i o n s of the muscles are -27-- c i t s -known to cause changes i n p r e s s u r e and impedance. The r e s u l t s of these i n v e s t i g a t i o n s are not as c o n c l u s i v e as those obtained from i n v e s t i g a t i o n s of CRM and TTS. G e n e r a l l y the number of s u b j e c t s employed i n the s t u d i e s was s m a l l and the v a r i a b i l i t y i n r e s u l t s was l a r g e . The f o l l o w i n g -tendencies were noted: the d u r a t i o n of impedance changes was longer w i t h s t i m u l a t i o n by n o i s e s than by pure tones and by low frequency s t i m u l i than by h i g h frequency s t i m u l i . In c o n c l u s i o n , the l i t e r a t u r e review has shown t h a t the r e s u l t s o b t a i n e d from r e s e a r c h i n t o middle ear muscle a c t i v i t y are i n c o n c l u s i v e and t h a t much r e s e a r c h concerning the a c t i v i t y of the middle ear muscles has s t i l l to be done. The purpose of the proposed r e s e a r c h was as f o l l o w s : (a) To i n v e s t i g a t e middle ear muscle a c t i v i t y d u r i n g s t i m u l a t i o n w i t h pure tones, octave band n o i s e , and o n e - t h i r d octave band n c i s e presented at the same SPL. (b) To study muscle a c t i v i t y d u r i n g exposure to s t i m u l i of d i f f e r e n t f r e q u e n c i e s . (c) To compare the t h r e s h o l d s of the a c o u s t i c r e f l e x f o r pure tones, octave band n o i s e , and o n e - t h i r d octave band n o i s e . Chapter 4 Exp e r i m e n t a l Apparatus and Procedure E x p e r i m e n t a l Design An o u t l i n e of the e x p e r i m e n t a l d e s i g n i s presented i n F i g u r e 6. Each t e s t s e s s i o n c o n s i s t e d of th r e e p a r t s : ' a one minute pre-exposure p e r i o d , a f i v e minute exposure p e r i o d , and a two minute post-exposure p e r i o d . During the pre-exposure and post-exposure p e r i o d s , impedance changes were recorded i n order t o e s t a b l i s h a b a s e l i n e . D u r i n g the exposure p e r i o d , s u b j e c t s r e c e i v e d a f i v e minute 114 dB SPL exposure t o one of three s t i m u l i . T h i s d u r a t i o n i s longer than r e p o r t e d i n most s t u d i e s , but McBay(1971) found t h a t a measurable impedance change was present even a f t e r f i v e minutes of s t i m u l a t i o n w i t h a 500 Hz pure tone presented at 118 dB SPL. S u b j e c t s i n t h i s study were d i v i d e d i n t o two groups and were exposed t o the f o l l o w i n g s t i m u l i : (a) pure tone, (b) octave band n o i s e , and (c) o n e - t h i r d octave band n o i s e . Ward(1962 b) suggested, "tha t perhaps i t would be more a p p r o p r i a t e t o compare the e f f e c t s of a pure tone of a p a r t i c u l a r frequency to those of an octave band whose upper c u t o f f , not c e n t e r frequency, i s f"(p.1617). He found t h a t a 1700 Hz pure tone "produced a p a t t e r n of TTS having a peak lower i n frequency than the p a t t e r n produced by the noise"(1200-2400 Hz octave band n o i s e ) (p. 1617). Based on p r e v i o u s r e s u l t s , Ward assumed t h a t the a c o u s t i c -29-One Minute Recording of Impedance Five Minute Recording of Impedance During Exposure to PT, TOBN,and OBN Two Minute Recording of Impedance PRE-EXPOSURE PERIOD EXPOSURE PERIOD POST-EXPOSURE PERIOD F i g . 6. Design of the experiment. -y\-r e f l e x c ould not have produced t h i s d i f f e r e n c e . I n experiments i n v o l v i n g a pure tone and n o i s e s w i t h upper c u t o f f s i m i l a r t o the frequency of the tone, Ward found t h a t the p a t t e r n of TTS a c r o s s v a r i o u s f r e q u e n c i e s was s i m i l a r f o r the d i f f e r e n t s t i m u l i . Ward r e p o r t e d t h a t the l a t t e r f i n d i n g confirmed h i s h y p o t h s i s t h a t the upper c u t o f f , not the center frequency, of the n o i s e was the important c h a r a c t e r i s t i c . T h u s , a c c o r d i n g t o Ward, pure tones of frequency x should be compared w i t h octave band n o i s e s w i t h c u t o f f f r e q u e n c i e s x/2 and x. " I f t h i s i s done, then the o n l y d i f f e r e n c e s i n e f f e c t s are due t o d i f f e r e n c e s i n s t r e n g t h of the a c o u s t i c r e f l e x under the two c o n d i t i o n s . 1 1 (Ward, 1962 b, p. 1618). Ward's formula was t h e r e f o r e used i n the present study s i n c e the i n v e s t i g a t o r was concerned, w i t h d e t e r m i n i n g d i f f e r e n c e s i n r e f l e x a c t i v i t y d u r i n g s t i m u l a t i o n w i t h tones and n o i s e . Group I s u b j e c t s were exposed to a 7 0 0 Hz pure tone, t o octave band n o i s e w i t h center frequency 5 0 0 Hz, and o n e - t h i r d octave band n o i s e w i t h center frequency 630 Hz; Group I I s u b j e c t s were exposed to a 1400 Hz pure tone, to octave band n o i s e w i t h center frequency 1000 Hz, and o n e - t h i r d octave band n o i s e w i t h center frequency 1 2 5 0 Hz. In order t o e l i m i n a t e p o s s i b l e i n t e r a c t i o n or sequence e f f e c t s the s t i m u l i were presented i n random order. F l e t c h e r ( 1 9 6 2 ) found t h a t 24- hours was "adequate f o r complete r e c o v e r y of t h r e s h o l d r e g a r d l e s s of the e x p e r i m e n t a l c o n d i t i o n s " ( p . 18) he used. Su b j e c t s i n t h i s study were -32-therefore given at least 24- hours rest between te s t sessions; generally t e s t sessions were scheduled 48 hours or more apart. Subjects Eighteen i n d i v i d u a l s who met the f o l l o w i n g c r i t e r i a served as subjects f o r t h i s study: (a) normal a i r conduction thresholds, with thresholds of 15 dB ISO or better f o r the frequency range 500 Hz to 2000 Hz, (b) normal middle ear function as determined by impedance audiometry, and (c) no h i s t o r y of o t o l o g i c a l problems. The subjects ranged i n age from 20 years to 59 years with a median age of 23 years. Nine subjects p a r t i c i p a t e d i n each of the two stimulus groups (described p r e v i o u s l y ) . Equipment Signal generation. A block diagram of the equipment i s shown i n Figure 7» Pure tone s t i m u l i were generated by an F33 Function Generator. The generator was i n i t i a l l y set to produce maximum acoustic output; t h i s s e t t i n g was not changed during the course of the study. Octave and one-third octave band noises were produced by a series of instruments. Random white noise, generated by a General Radio 1382 Random Noise Generator, was f i l t e r e d by a Br i i e l and Kjaer(B & K ) Bandpass F i l t e r Set Type 1612. The output of the f i l t e r was then amplified. Equipment settings f o r each noise remained constant throughout t e s t sessions. Manipulations of stimulus i n t e n s i t y were accomplished by adjusting the s e t t i n g of a Hewlett Packard 350D Attenuator. S t i m u l i were presented to subjects v i a a Grason-Stadler Graphic Impedance Recorder Bridge Transformer Pre-amplifier & Filter Noise Amplifier Generator Pure Tone Generator F i g . 7. Block diagram: Equipment f o r generating pure tones and noises. -34-TDH 39-300Z earphone with NAP 48490-1 cushion. C a l i b r a t i o n . Ambient noise measured i n the te s t room with a B & K P r e c i s i o n Sound Level Meter Type 2203 was le s s than 45 dBA SPL. Analysis by octave band f i l t e r s ( B & K Octave F i l t e r Set Type 1613) indicated ambient noise consisted mainly of frequencies below 250 Hz. For the octave bands with center frequencies 250, 500, 1000, 2000, 4000, 8000, and 16000 Hz the average noise l e v e l was 25.9 dB SPL. On each t e s t day, the acoustic output of the s i g n a l generator with earphone unit was measured using the B & K P r e c i s i o n Sound Level Meter and A r t i f i c i a l Ear Type 4152. Values i n SPL in d i c a t e pressure l e v e l s measured i n a 6-cc N.B.3. 9A Coupler. The average SPL of the 700 Hz and 1400 Hz pure tones, f o r a l l t e s t sessions, was 114.99 dBA (standard deviation(S.D.) 0.41) and 114.72 dBA(S.D. 0.50), r e s p e c t i v e l y . For noise s t i m u l i , the l e v e l around which the meter needle f l u c t u a t e d evenly was considered the SPL reading. The average SPL reading of the 500 Hz and 1000 Hz octave band noises f o r a l l sessions was 114.24 dBA (S.D. 0.33) and 114.17 dBA(3.D. 0.55), r e s p e c t i v e l y ; and, of the 630 Hz and 1250 Hz one-third octave band noises was 114.08 dBA(3.D. 0.52) and 114.95 dBA(S.D. 0.54), r e s p e c t i v e l y . Impedance measurements. When the middle ear muscles contract, the impedance of the ear i s a l t e r e d . In t h i s study, a Madsen Electroacoustic Impedance Bridge Model ZO 70 was used to monitor changes i n the impedance which occurred during acoustic s t i m u l a t i o n . -35-Employing t h i s t e c h n ique, a 220 Hz tone i s i n t r o d u c e d i n t o the e x t e r n a l a u d i t o r y meatus v i a a probe s e a l e d i n the c a n a l . The i n t e n s i t y of the tone i s a d j u s t e d u n t i l the SPL i n the ear c a n a l i s V5 dB. Any changes i n the impedance of the ear w i l l a l t e r the SPL i n the c a n a l , and these changes are shown i n the liadsen b r i d g e by d e f l e c t i o n s of the balance meter needle. In order t o secure a permanent r e c o r d , s i m i l a r v o l t a g e changes which caused the meter d e f l e c t i o n s were recorded on c h a r t paper u s i n g a Devices graphic r e c o r d e r which had an "excursion of 55 m i l l i m e t e r s . The Madsen b r i d g e and graphic r e c o r d e r were set at the same s e n s i t i v i t y s e t t i n g throughout t e s t s e s s i o n s . Procedure P r i o r to t e s t i n g , each s u b j e c t was g i v e n g e n e r a l i n f o r m a t i o n about the purpose of t h i s study. S u b j e c t s were comfortably seated next t o the equipment i n such a way t h a t they c o u l d not see t h e i r responses t o s t i m u l a t i o n . For each s u b j e c t , the ear w i t h the lowest pure tone t h r e s h o l d s a c r o s s the frequency range 500 Hz to 2000 Hz was chosen as the ear to be exposed. In both groups, f i v e l e f t and f o u r r i g h t ears were exposed. A l l s u b j e c t s were given standard i n s t r u c t i o n s which are presented i n the Appendix. The f o l l o w i n g procedure was used f o r a l l s u b j e c t s : (a) a p l u g attached to the probe was i n s e r t e d i n the c a n a l and an a i r - t i g h t s e a l was o b t a i n e d , (b) the middle ear p r e s s u r e was determined u s i n g standard methods and the b r i d g e was set at t h i s p r e s s u r e , -56-( c ) the impedance was r e c o r d e d f o r one minute t o e s t a b l i s h a p re-exposure b a s e l i n e , (d) the impedance was r e c o r d e d f o r f i v e minutes d u r i n g a c o u s t i c s t i m u l a t i o n , (e) f o l l o w i n g removal o f the s t i m u l u s the impedance was r e c o r d e d f o r two minutes t o e s t a b l i s h a p o s t - e x p o s u r e b a s e l i n e , and ( f ) the p l u g was checked t o make sure t h e r e was s t i l l a s e a l . T h r e s h o l d s f o r the a c o u s t i c r e f l e x were found u s i n g s t a n d a r d a s c e n d i n g - d e s c e n d i n g p r o c e d u r e s . Data Measurement T r a c e s o f the impedance, c h a n g e s ( F i g u r e 8) d u r i n g a c o u s t i c s t i m u l a t i o n were measured i n terms o f m i l l i m e t e r s of d e f l e c t i o n from the b a s e l i n e . The b a s e l i n e f o r each t r a c e was d e t e r m i n e d by drawing a l i n e from the l e v e l 15 seconds pre-exposure t o the l e v e l one minute p o s t -e xposure. The l e v e l a t one minute p o s t - e x p o s u r e was chosen s i n c e the m a j o r i t y of s u b j e c t s had r e a c h e d a s t a b l e l e v e l by t h i s t i me. The a b s o l u t e impedance change o f the e a r d u r i n g s t i m u l a t i o n c o u l d not be determined u s i n g the setup i n t h i s s t u d y; but the r e l a t i v e impedance change c o u l d be i n f e r r e d from the amount o f d e f l e c t i o n , i . e . , the l a r g e r the d e f l e c t i o n , the g r e a t e r the impedance change, and the g r e a t e r the muscle c o n t r a c t i o n . Twenty measurements were t a k e n d u r i n g the f i v e minute p e r i o d , i . e . , one measurement was done every 15 seconds. The d e f l e c t i o n s were measured t o the n e a r e s t 0.25 m i l l i m e t e r . 0 6 0 Baseline 1 2 0 1 8 0 2 4 0 3 0 0 Onset of Stimulus Stimulation TIME (sec) Removed F i g . 8 . S c h e m a t i c d i a g r a m : T r a c e o f i m p e d a n c e c h a n g e d u r i n g a c o u s t i c s t i m u l a t i o n Chapter 5 Results S t a t i s t i c a l Analysis Data obtained from both groups of subjects were separately submitted to s t a t i s t i c a l analyses, s p e c i f i c a l l y s i n g l e - f a c t o r or two-factor analyses of variance(ANOV) f o r repeated measures(Bruning and K i n i t z , 1968, pp. 4-3-54; Winer, 1962, pp. 105-124). For the a n a l y s i s , the data were divided i n t o : (a) Time(T)—the time at which the ra t i o s ( d e s c r i b e d below) were ca l c u l a t e d , and (b) Condition (0)—the type of stimulus e i t h e r pure tone(PT), one-third octave band noise(TOBN), or" octave band noise(OBN). When the ANOV revealed a s i g n i f i c a n t F, the Newman-Keuls method(Winer, 1962, pp.80-85) was used to probe "the nature of the difference between treatment means"(Winer, 1962, p. 80). Threshold of the Acoustic Reflex • The threshold of the acoustic r e f l e x was determined f o r a l l subjects f o r each stimulus. For Group I subjects the mean pure tone threshold was 93.44 dBA SPL(S.D. 5.88), mean one-third octave band threshold was 91.67 dBA SPL (S.D. 8.94), and mean octave band threshold was 89.22 dBA SPL(S.D. 8.09). Although the mean pure tone threshold was higher than the mean threshold f o r noise, the MOV indicated these d i f f e r e n c s were not s t a t i s t i c a l l y s i g n i f i c a n t ( T a b l e I ) . For Group I I subjects the mean pure tone threshold -38--39-T a b l e I . A n a l y s i s o f V a r i a n c e : T h r e s h o l d as a f u n c t i o n o f c o n d i t i o n f o r the n i n e s u b j e c t s i n Group I . Source of V a r i a t i o n SS d f MS T o t a l 1520.69 26 S u b j e c t s 1200.69 8 Treatment 80.88 2 40.44 2.71 E r r o r 239.13 16 14.95 -40-was 9 4 . 8 9 dBA SPL(S.D. 7 . 9 1 ) , mean o n e - t h i r d octave hand t h r e s h o l d was 9 0 . 8 9 dBA SPL(S.D. 8 . J 4 ) , and mean octave band t h r e s h o l d was 8 9 . 1 1 dBA SPL(S.D. 8 . 7 8 ) . A n a l y s i s ( T a b l e I I ) r e v e a l e d a s t a t i s t i c a l l y s i g n i f i c a n t o v e r a l l P v a l u e . A Newman-Keuls p r o b e ( T a b l e I I I ) was conducted and i n d i c a t e d t h a t d i f f e r e n c e s between pure tone and octave band t h r e s h o l d s were s t a t i s t i c a l l y s i g n i f i c a n t and between pure tone and o n e - t h i r d o c t a v e band t h r e s h o l d s were c l o s e t o s i g n i f i c a n c e . S i x t h r e s h o l d s were r e p e a t e d and found t o be w i t h i n 2 dB o f the i n i t i a l t h r e s h o l d v a l u e s . R e f l e x A c t i v i t y Maximum s i z e o f pen d e f l e c t i o n ( I n i t i a l s t r e n g t h o f  the r e f l e x ) . When the s t i m u l i were p r e s e n t e d t o s u b j e c t s , pen d e f l e c t i o n , i . e . , muscle c o n t r a c t i o n , i n c r e a s e d r a p i d l y . Por the m a j o r i t y o f s u b j e c t s , maximum d e f l e c t i o n was r e a c h e d w i t h i n the f i r s t 20 seconds a f t e r onset o f s t i m u l a t i o n . The maximum d e f l e c t i o n i n the f i r s t 20 seconds was t a k e n as an i n d i c a t o r o f the i n i t i a l s t r e n g t h o f the a c o u s t i c r e f l e x . The s u b j e c t s were rank o r d e r e d a c c o r d i n g t o the s i z e o f the pen d e f l e c t i o n f o r each s t i m u l u s ( P i g u r e s 9 and 1 0 ) . A c r o s s groups and s t i m u l i , the s i z e o f d e f l e c t i o n v a r i e d from a minimum of 9 m i l l i m e t e r s t o a maximum of 55 m i l l i m e t e r s . A n a l y s e s ( T a b l e s IV and V) i n d i c a t e d t h e r e were no s i g n i f i c a n t d i f f e r e n c e s i n i n i t i a l s i z e o f the r e f l e x between c o n d i t i o n s . Three t e s t on two s u b j e c t s were r e p e a t e d a p p r o x i m a t e l y Table I I . A n a l y s i s of Va r i a n c e : Threshold as a f u n c t i o n of c o n d i t i o n f o r the nine s u b j e c t s i n Group I I . Source of V a r i a t i o n SS df MS F T o t a l S u b j e c t s Treatment 1832.31 1524.94 157-63 26 8 2 78.81 * * 8.42 E r r o r 149-75 16 9-36 Table I I I . Newman-Keuls Test: S i g n i f i c a n c e of d i f f e r e n c e s between t h r e s h o l d s f o r each c o n d i t i o n i n Group I I . C o n d i t i o n OBN TOBN PT T o t a l 802 818 854 OBN 802 16 * * 52 TOBN 818 36 Truncated r 2 3 q.99 ( r , 1 6 ) J n x Moerror 37.90 43.88 ** p<.01 55-50-45-40-35-„ 30-I 2 5 ' z 2 0 -Q 15-*< 10-i n" 9 3 Q Z o 55" 50-O 45-IM 40-35-30-to 25" £T. 20-w 15-^ 10--Z 5-z o 1 -o p u LL. 11 1 55-Q 50-z 45-LLI 40-—* 35-% 30-X i 25-20-15-' 10-5-o-L 3 1 5 8 7 4 3 9 SUBJECTS IN RANK ORDER 6 1 F i g . 9- I n i t i a l s t r e n g t h of a c o u s t i c r e f l e x , .as i n d i c a t e d by the s i z e o f maximum pen d e f l e c t i o n i n the f i r s t 20 seconds o f s t i m u l a t i o n , f o r each s u b j e c t i n Group I . A, 700 Hz FT; B, 630-.-Hz. .TOBNy/and C, 500 Hz OBN. -43-55" 50-45-40-35-30-E 25-ATION (m 20-15-10--iTIMUL 5-0-L to u -O 55"+ to Q 50-O 45-y 40-35-8 30-175 25-£ 20-15-10-5--0-u-i z z o ti !S 55-& 50--£ 40-^ 35-j 30--25" x < 5 20-15-10-5-0-8 1 2 2 9 C 5 7 4 2 9 8 SUBJECTS IN RANK ORDER 3 1 F i g . 10. I n i t i a l s t r e n g t h o f a c o u s t i c : . r e f l e x , as i n d i c a t e d by the s i z e o f maximum pen d e f l e c t i o n i n the f i r s t 20 seconds o f s t i m u l a t i o n , f o r each s u b j e c t i n Group I I . A, 1400 Hz PT; B, 1250 Hz TOBN; and C, 1000 Hz OBN. -44-T a b l e IV. A n a l y s i s o f V a r i a n c e : I n i t i a l s i z e o f the a c o u s t i c r e f l e x , as a f u n c t i o n o f c o n d i t i o n f o r the n i n e s u b j e c t s i n Group I . Source of V a r i a t i o n SS d f MS F T o t a l 4724.76 26 S u b j e c t s 2952.01 8 Treatment 493.73 2 246.86 3.09 E r r o r 1279.02 16 79.94 T a b l e V. A n a l y s i s o f V a r i a n c e : I n i t i a l s i z e o f the a c o u s t i c r e f l e x , as a f u n c t i o n o f c o n d i t i o n f o r the n i n e s u b j e c t s i n Group I I . Source o f V a r i a t i o n SS d f MS F T o t a l 5352.56 26 S u b j e c t s 3252.22 8 Treatment 168.34 2 84.17 0.70 E r r o r 1931.99 16 120.75 IP-t h r e e weeks a f t e r o r i g i n a l t e s t i n g . The maximum d e f l e c t i o n was determined and compared t o the o r i g i n a l v a l u e s ( F i g u r e 11). V a r i a b i l i t y i n the r e s p o n s e s was g e n e r a l l y l e s s t h an 15 m i l l i m e t e r s . R e f l e x decay. R e f l e x decay was determined f o r each s t i m u l u s by c a l c u l a t i n g t he r a t i o o f pen d e f l e c t i o n a t 300 seconds t o maximum d e f l e c t i o n i n the f i r s t 20 seconds. When the r a t i o was l a r g e ( i . e . , c l o s e t o one), decay v/as assumed t o be s m a l l . With s m a l l decay muscle c o n t r a c t i o n remained a t a l e v e l c l o s e t o the i n i t i a l d e f l e c t i o n , i . e . , r e l a x a t i o n o f the muscle was slow. In F i g u r e 12 and 13 decay v a l u e s are p l o t t e d f o r s u b j e c t s i n Group I and Group I I , r e s p e c t i v e l y . The r a t i o f o r OBN was g r e a t e r t han the v a l u e o f the r a t i o f o r PT f o r a l l s u b j e c t s . A s i m i l a r p a t t e r n was found f o r PT and TOBN except f o r s u b j e c t s 3 and 4- i n Group I and s u b j e c t 1 i n Group I I . S t a t i s t i c a l a n a l y s e s i n d i c a t e d t h e r e was a s i g n i f i c a n t o v e r a l l d i f f e r e n c e between the decay v a l u e s f o r PT, TOBN, and OBN(Tables VI and V I I I ) . F o r Group I , a Newman-Keuls t e s t i n d i c a t e d a s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e i n decay between PT and 0BN(Table V I I ) ; f o r Group I I , t h e r e was a s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e between PT and both n o i s e s ( T a b l e I X ) . A c t i v i t y w i t h time. The r a t i o o f pen d e f l e c t i o n a t time t seconds t o maximum d e f l e c t i o n i n the f i r s t 20 seconds was c o n s i d e r e d i n d i c a t i v e o f the amount of muscle c o n t r a c t i o n -46-8 z o u LU CO O CN 55-50-45-40-35-30-25-20-I 15-"-•^lO-' 5-^ Z 0-0^55- -t j W O -Su.45--SO40.. 35--30-• 25-20-. 15--10--5--o-L Z L U X Q INITIAL TEST QJjRETEST PT TOBN OBN B PT TOBN CONDITION OBN F i g . 1 1 . C o m p a r i s o n o f o r i g i n a l a n d r e t e s t v a l u e s o f t h e i n i t i a l s t r e n g t h o f a c o u s t i c r e f l e x f o r t h r e e c o n d i t i o n s f o r S u b j e c t s A a n d B. 1.0-0.9-Q 8 g o.8-z 8 LU to o o ro Z o d z uu LO o CN I o z o t— u LU L l _ LU Q 0.7--0.6--0.5--0.4-| 0.3' x | 0.2' 0.1-§ 7 0 0 Hz FT Q 6 3 0 Hz TOBN Hz OBN 1 5 SUBJECT P i g . 12. R e f l e x d e c a y , a s i n d i c a t e d b y t h e r a t i o o f p e n d e f l e c t i o n a t 300 s e c o n d s t o maximum d e f l e c t i o n i n t h e f i r s t 20 s e c o n d s , f o r s u b j e c t s i n G r o u p I. l.O-' 0.94 18 Z <dO 0.8-o z o u U J to o CN I 0.7-§ ° 0.6-CO pz 0.5"• L U z LU -O x < O.i-0.3-• 0.2-0.1-• §1400 Hz PT Q]l250 Hz TOBN [JlOOO Hz OBN 5 SUBJECT Pig. 1 3 - Reflex decay, as indicated by. the ratio of pen deflection at 300 seconds to maximum deflection i n the f i r s t 2 0 seconds, for subjects in Group I I . T a b l e V I . A n a l y s i s o f V a r i a n c e : R e f l e x decay as a f u n c t i o n o f c o n d i t i o n f o r the', n i n e s u b j e c t s i n Group I . Source of V a r i a t i o n SS d f MS F T o t a l 1 . 5 2 26 S u b j e c t s 0.8? 8 Treatment 0.38 2 0.19 * * 11.56 E r r o r 0 . 2 7 16 0.02 T a b l e V I I . Newman-Keuls T e s t : S i g n i f i c a n c e o f d i f f e r e n c e s between r e f l e x decay f o r each c o n d i t i o n i n Group I . C o n d i t i o n PT TOBN OBN T o t a l 4 . 2 3 5.48 6 . 8 5 PT 4 . 2 3 1 . 2 5 * * 2.62 TOBN 5.48 1-37 T r u n c a t e d r 2 3 q . 9 9 ( r , 1 6 ) 7 n x MSerror 1 . 7 3 2.01 ** p<.01 T a b l e V I I I . A n a l y s i s o f V a r i a n c e : R e f l e x decay as a f u n c t i o n o f c o n d i t i o n f o r the n i n e s u b j e c t s i n Group I I . . Source of V a r i a t i o n SS d f MS T o t a l 2.35 26 S u b j e c t s 1.20 8 Treatment 0.83 2 0.41 * * 20.00 E r r o r 0.33 16 0.02 T a b l e IX. Newman-Keuls T e s t : S i g n i f i c a n c e o f d i f f e r e n c e s between r e f l e x decay f o r each c o n d i t i o n i n Group I I . C o n d i t i o n PT TOBN OBN T o t a l " 2.45 5.67 5.89 PT 2.45 * * 3.22 * * 3.44 TOBN 5.67 0.22 T r u n c a t e d r 2 3 q.99 (r,16)vAi x MSerror 1.73 2.01 ** p<.01 r e m a i n i n g a t time t , assuming maximum d e f l e c t i o n was e q u i v a l e n t to a r a t i o o f one. D u r i n g a c o u s t i c s t i m u l a t i o n t h e r e was a p r o g r e s s i v e d e c r e a s e i n muscle a c t i v i t y . F o r Group I ( F i g u r e 14), the degree o f muscle c o n t r a c t i o n was s i m i l a r f o r the t h r e e c o n d i t i o n s up t o 90 seconds o f s t i m u l a t i o n . A f t e r t h i s time, muscle a c t i v i t y d u r i n g PT and TOBN s t i m u l a t i o n began t o d ecrease f a s t e r than during.OBN s t i m u l a t i o n . A t w o - f a c t o r ANOV (T a b l e X) r e v e a l e d a s t a t i s t i c a l l y s i g n i f i c a n t Time x C o n d i t i o n i n t e r a c t i o n . A Newman-Keuls t e s t ( T a b l e XI) i n d i c a t e d t h a t t h e r e were no s i g n i f i c a n t d i f f e r e n c e s i n muscle a c t i v i t y f o r the t h r e e c o n d i t i o n s below 120 seconds; by 270 seconds, s t a t i 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 s began to appear. F o r Group I I , the p a t t e r n was somewhat d i f f e r e n t ( F i g u r e 15). Muscle a c t i v i t y d u r i n g PT s t i m u l a t i o n was s u b s t a n t i a l l y l e s s t han d u r i n g n o i s e s t i m u l a t i o n ; a c t i v i t y d u r i n g TOBN and OBN s t i m u l a t i o n appeared s i m i l a r . The ANOV(Table X I I I ) i n d i c a t e d t h e r e was a s i g n i f i c a n t F f o r C o n d i t i o n . The Newman-Keuls(Table XIV) r e v e a l e d a s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e i n muscle a c t i v i t y between PT and OBN and between PT and TOBN a c r o s s a l l t i m e s . The a n a l y s e s o f v a r i a n c e f o r b o t h groups i n d i c a t e d t h a t the p o i n t i n time at which the r a t i o s were c a l c u l a t e d had a s i g n i f i c a n t e f f e c t on the amount o f muscle c o n t r a c t i o n r e c o r d e d ( T a b l e s X and X I I I ) . A Newman-Keuls probe was P0.6 0.5 z z oQ 111 J J uji! 0.4 §§ 0.3-x < 0.2 0.1-' 0-20 O 700 Hz PT A 630 Hz TOBN • 500 Hz OBN 30 60 90 120 150 180 210 240 270 i ro i 300 TIME t (sec) F i g . 14. Muscle a c t i v i t y , as i n d i c a t e d by t h e r a t i o o f pen d e f l e c t i o n a t time t seconds t o maximum d e f l e c t i o n i n the f i r s t 20 seconds, as a f u n c t i o n o f time f o r PT, TOBN, and OBN c o n d i t i o n s . Each p o i n t r e p r e s e n t s the mean va l u e o f the n i n e s u b j e c t s i n Group I. T a b l e X. A n a l y s i s o f V a r i a n c e : Muscle a c t i v i t y as a f u n c t i o n of time and c o n d i t i o n f o r the n i n e s u b j e c t s i n Group I . Source of V a r i a t i o n SS d f MS F T o t a l 15.97 242 S u b j e c t s 8.10 8 Time(T) 1.19 8 0.15 * * 12.72 T x S u b j e c t s 0.75- 64 0.01 C o n d i t i o n ( G ) 0.99 2 0.50 2.16 C x S u b j e c t s 5.67 16 0.23 T x C 0.39 16 0.03 * * 3.47 T x C x S u b j e c t s 0.90 128 0.01 ** p<.01 -54-T a b l e X I . Newman-Keuls T e s t : S i g n i f i c a n c e o f d i f f e r e n c e s between c o n d i t i o n s as a f u n c t i o n o f time f o r Group I . t=300 sec C o n d i t i o n PT TOBN OBN T o t a l 4.23 5.48 6.85 PT 4.23 TOBN 5-48 T i T T 1.25 2.62 1.37 t=240 sec C o n d i t i o n PT TOBN OBN T o t a l 5-06 5-56 6.94 PT 5.06 TOBN 5-56 0.50 1.88 1.38 1 T T * * t=180 sec C o n d i t i o n T o t a l TOBN PT OBN 5.97 6.13 7.07 TOBN 5-97 PT 6.13 0.16 1.10 0.94 t=120 sec C o n d i t i o n PT TOBN OBN T o t a l 6.06 6.89 6.98 PT 6.06 TOBN 6.89 0.83 0.92 0.09 t=270 sec C o n d i t i o n PT TOBN OBN T o t a l 4.29 5.54 6.80 PT 4.29 TOBN 5.54 T7 TT 1.25 2.51 1.26^ t=210 sec PT 5-16 TOBN 5.86 t a l . 5 0 sec PT 5-73 TOBN 6.19 0.46 C o n d i t i o n PT TOBN OBN T o t a l 5-16 5.86 6.86 "TT 0.70 1.70 1.00 C o n d i t i o n PT TOBN OBN T o t a l 5-73 6.19 7.17 1.44 0.98 T r u n c a t e d r 2 3 q.99 (r,128)7n x MSerror 1.11 1.26 p<-01 Table X I I . Newman-Keuls Test: S i g n i f i c a n c e , of d i f f e r e n c e s i n muscle a c t i v i t y w i t h time f o r Group I . Time(sec) 300 270 240 210 150 180 120 90 60 T o t a l 16.56 16.63 17-56 17.88 19.09 19.17 19.93 21.37 22.38 300 16.56 0.07 1.00 1.32 * * 2.53 * * 2.61 * * 3-37 * * 4.81 ** 5.82 270 16.63 0.93 1.25 * * 2.46 * * 2.54 * * 3.30 * * 4.74 ** 5.75 240 17.56 0.32 1.53 1.61 2.37 * * 3.81 ** 4.82 210 17.88 1.21 1.29 2.05 * * 3.49 ** 4.50 150 19.09 0.08 0.84 2.28 ** 3.29 180 19.17 0.76 2.20 ** 3.21 120 19.93 1.44 ** 2.45 90 21.37 1.01 Truncated r 2 3 4 5 6 7 8 9 q.99 (r,64)V n x MSerror 1.96 2.22 2.39 2.50 2.59 2.66 2.72 2.78 ** p<.01 0.1-• OH 1 1 1 1 1 1 1 1 1 r -0-20 30 60 90 120 150 180 210 240 270 300 TIME r (sec) F i g . 15- Muscle a c t i v i t y , as i n d i c a t e d by the r a t i o of pen d e f l e c t i o n at time t seconds to maximum d e f l e c t i o n i n the f i r s t 20 seconds, as a f u n c t i o n of time f o r PT, TOBN, and OBN c o n d i t i o n s . Each .point r e p r e s e n t s the mean value of the nine s u b j e c t s i n Group I I . T a b l e X I I I . A n a l y s i s o f V a r i a n c e : Muscle a c t i v i t y as a f u n c t i o n o f time and c o n d i t i o n f o r the n i n e s u b j e c t s i n Group I I . Source o f V a r i a t i o n SS d f MS F T o t a l 20.61 242 S u b j e c t s 8.83 8 Time(T) 1.75 8 0.22 * * 20.35 T x S u b j e c t s 0.69 64 0.01 C o n d i t i o n ( C ) 5-54- 2 2.77 * * 14.54-0 x S u b j e c t s 3.05 16 0.19 T x G 0.08 16 O.Oi 0.94 T x C x S u b j e c t s 0.67 128 0.01 T a b l e XIV. Newman-Keuls T e s t : S i g n i f i c a n c e of. d i f f e r e n c e s between c o n d i t i o n s a c r o s s a l l times f o r Group I I . C o n d i t i o n PT TOBN OBN T o t a l 35-75 58.69 63-90 PT 35.75 * * 22.94 * * 28.15 TOBN 58.69 5.21 T r u n c a t e d r 2 3 q.99 (r,16)7n x MSerror 16.19 18.74 ** p<.01 Table XV. Newman-Keuls Test: S i g n i f i c a n c e , of d i f f e r e n c e s i n muscle a c t i v i t y w i t h time f o r Group I I . Time(sec) 500 270 240 210 180 150 120 90 60 T o t a l 14.01 15.16 15.71 16.51 17.47 18.60 19.60 20.29 20.99 300 14.01 1.15 1.70 * * 2.50 * * 3.46 * * 4.59 * * 5.59 * * 6.28 ** 6.98 270 15.16 0.55 1.35 2.31 * * 3.44 * * 4.44 * * 5.13 *•* 5.83 240 15.71 0.80 1.76 * * 2.89 * * 3.89 * * 4.58 ** 5.28 210 16.51 0.96 2.09 * * 3.0.9 * * 3-78 ** 4.48 180 17.47 1.13 2.13 * * 2.82 ** 3.52 150 18.60 1.00 1.69 ** 2.39 120 19.60 0.69 1.39 90 20.29 0.70 Truncated r 2 3 4 5 6 7 8 9 q.99 (r,64)7 n x MSerror 1.96 2.22 2.39 2.50 2.59 2 . 6 6 2.72 2.78 ** p<,01 - 5 9 -conducted t o e l u c i d a t e the d i f f e r e n c e s i n muscle a c t i v i t y , due to time, over a l l s u b j e c t s and a l l c o n d i t i o n s ( T a b l e s X I I and XV). There were s i g n i f i c a n t d i f f e r e n c e s between the f i r s t and l a s t one and a h a l f minutes o f s t i m u l a t i o n . There were no s i g n i f i c a n t d i f f e r e n c e s from 210 seconds t o 3 0 0 seconds f o r Group I or from 240 seconds t o 3 0 0 seconds f o r Group I I . R e l i a b i l i t y o f Measurements The r e l i a b i l i t y o f the measurements was e s t i m a t e d by comparing r e p e a t e d measurements on randomly chosen t r a c e s at v a r i o u s t i m e s . F o r i n t r a m e a s u r e r r e l i a b i l i t y , 100 measurements, a p p r o x i m a t e l y 10$ o f the t o t a l , were reworked, and the v a l u e s o b t a i n e d were compared t o the f i r s t v a l u e s o b t a i n e d . A P e a r s o n Product-Moment c o r r e l a t i o n c o e f f i c i e n t gave an r of 0.999889. I n t e r m e a s u r e r r e l i a b i l i t y v/as determined by comparing 60 measurements, done s e p a r a t e l y by two p e o p l e , t o the o r i g i n a l v a l u e s r e c o r d e d by the i n v e s t i g a t o r . The P e a r s o n r ' s o b t a i n e d were 0.999666 and 0.999599. In view o f the s e h i g h c o r r e l a t i o n s the r e l i a b i l i t y o f the measurements was c o n s i d e r e d t o be good. Chapter 6 D i s c u s s i o n and Conclusions T h i s r e s e a r c h was undertaken t o study middle ear muscle a c t i v i t y d u r i n g prolonged s t i m u l a t i o n . S p e c i f i c a l l y , i t was concerned w i t h comparing r e f l e x t h r e s h o l d s f o r PT, TOBN, and OBN; w i t h s t u d y i n g middle ear muscle a c t i v i t y d u r i n g f i v e minutes of s t i m u l a t i o n w i t h these s t i m u l i ; and w i t h comparing a c t i v i t y f o r s t i m u l i of d i f f e r e n t frequency. Before d i s c u s s i n g the r e s u l t s of t h i s study, i t i s a d v i s a b l e to mention some aspects of muscle a c t i v i t y , s i n c e i n p r i n c i p l e the middle ear muscles should behave i n a manner s i m i l a r to other s k e l e t a l muscles. General Muscle A c t i v i t y C o n t r a c t i o n of s k e l e t a l muscle i s c o n t r o l l e d by r e f l e x and v o l u n t a r y a c t i v i t y of the c e n t r a l nervous system(Woodbury, Gordon, and Conrad, 1965). The motor u n i t , which c o n s i s t s of one motoneuron, i t s axons, and the muscle f i b r e s i t i n n e r v a t e s , i s the fundamental u n i t ; a t w i t c h c o n t r a c t i o n of one motor u n i t i n response to one impulse i n the u n i t ' s motoneuron i s the weakest muscular response. As the frequency of impulses down a motor nerve i s i n c r e a s e d , the f o l l o w i n g occur " i n an o v e r l a p p i n g sequence: ( i ) more motor u n i t s are a c t i v a t e d ( r e c r u i t m e n t ) ; ( i i ) the a c t i v e motor u n i t s d i s c h a r g e more f r e q u e n t l y but not r a p i d l y enough f o r muscular summation ( i . e . , the response i s s u b t e t a n i c ) ; and ( i i i ) w i t h f u r t h e r i n c r e a s e of frequency, the motor u n i t t w i t c h e s summate t o form a t e t a n u s . In both stage ( i i ) and stage ( i i i ) , the more r a p i d the frequency the g r e a t e r the t e n s i o n becomes." (V/oodbury et a l , 1965, p. 132) -60-- b ' l -When a maximal s t i m u l u s i s presented t o ;a. motor nerve, a l l f i b r e s of the muscle are a c t i v e and muscle t e n s i o n reaches maximum. For s t i m u l a t i o n above maximal i n t e n s i t y , "the response w i l l not be g r e a t e r than t h a t to a maximal stimulus"(Woodbury et a l , 1965, p. 127) u n l e s s two maximal s t i m u l i are presented so c l o s e t o g e t h e r t h a t c o n t r a c t i o n from the f i r s t s t i m u l u s i s not f i n i s h e d before c o n t r a c t i o n from the second s t i m u l u s b e g i n s . When s e v e r a l s t i m u l i are presented i n r a p i d s u c c e s s i o n , each s t i m u l u s adds, i . e . , summates, to the p r e v i o u s ones u n t i l a p o i n t i s reached where there i s no f u r t h e r i n c r e a s e i n muscle t e n s i o n and c o n t r a c t i o n i s maintained. At t h i s p o i n t " a l l c o n t r a c t i l e elements are . maximally activated"(Woodbury et a l , 1965, p. 128), and the response i s known as t e t a n u s . I n summary, the o v e r a l l t e n s i o n e x e r t e d on the tendons of a muscle at a p a r t i c u l a r time i s the sum of the t e n s i o n s produced by the i n d i v i d u a l motor u n i t s at t h a t time. Threshold of the A c o u s t i c R e f l e x For s u b j e c t s i n t h i s study, t h r e s h o l d s were h i g h e r f o r pure tones than n o i s e ; but the d i f f e r e n c e between these s t i m u l i was o n l y s t a t i s t i c a l l y s i g n i f i c a n t f o r PT and OBN f o r Group I I s u b j e c t s . I t i s d i f f i c u l t to compare r e s u l t s of t h i s study w i t h others s i n c e many r e p o r t t h r e s h o l d s i n 3L not SPL. Pure tone t h r e s h o l d s evidenced by s u b j e c t s i n t h i s study are h i g h e r than t h r e s h o l d s r e p o r t e d by Hung and Dallos(1972) u s i n g the -62-impedance method, and are lower than t h r e s h o l d s r e p o r t e d by Weiss, Mundie, C a s h i n , and Shinabarger(1962) u s i n g tympanometry. Few s t u d i e s have determined t h r e s h o l d s f o r OBN. U s i n g s t i m u l i o f d i f f e r e n t f r e q u e n c i e s , D j u p e s l a n d e t a l(1966) r e p o r t e d OBN t h r e s h o l d s f o r t h r e e s u b j e c t s which were lower than t h r e s h o l d s o b t a i n e d i n t h i s s t u d y . A l t h o u g h t h r e s h o l d v a l u e s o b t a i n e d i n o t h e r s t u d i e s are not d i r e c t l y comparable, most s t a p e d i u s r e f l e x t h r e s h o l d s r e p o r t e d were lower f o r n o i s e t h a n f o r pure t o n e s ( D e u t s c h , 1972; D j u p e s l a n d e t a l , 1966); t h i s f i n d i n g agrees w i t h t h e r e s u l t s o f t h i s s t u d y . S t i m u l u s bandwidth may be a f a c t o r t o be c o n s i d e r e d i n n o t i n g the d i f f e r e n c e s between PT, TOBN, and OBN, s i n c e t h r e s h o l d s were seen t o d e c r e a s e as bandwidth i n c r e a s e d . I t i s known t h a t wide band s t i m u l i e x c i t e a l a r g e r a r e a o f the b a s i l a r membrane th a n narrow band s t i m u l i ; c o n s e q u e n t l y i t may be assumed t h a t n o i s e s t i m u l a t i o n would a c t i v a t e more nerve f i b r e s and motor u n i t s t h a n pure tone s t i m u l a t i o n a t the same i n t e n s i t y . G i v e n t h a t a c e r t a i n degree o f muscle c o n t r a c t i o n i s n e c e s s a r y to produce a d e t e c t a b l e impedance change, i t f o l l o w s t h a t n o i s e s t i m u l a t i o n would produce t h i s amount of c o n t r a c t i o n b e f o r e t o n a l s t i m u l a t i o n s i n c e n o i s e would a c t i v a t e the r e q u i s i t e number of motor u n i t s at a lower i n t e n s i t y . R e f l e x A c t i v i t y F o r most o f the s u b j e c t s i n t h i s study, maximum muscle r e s p o n s e ( i n d i c a t e d by pen d e f l e c t i o n ) o c c u r r e d - c o -i n t he f i r s t 20 seconds a f t e r onset o f s t i m u l a t i o n ; t h i s a g r ees w i t h d a t a r e p o r t e d by McBay(1971). The s i z e o f the maximum response v a r i e d w i d e l y between s u b j e c t s ( 9 m i l l i m e t e r s to 55 m i l l i m e t e r s ) and l e s s w i t h i n s u b j e c t s ( g e n e r a l l y l e s s t han 20 m i l l i m e t e r s ) . U n expectedly l a r g e c o n t r a c t i o n s ( i . e . , c o n t r a c t i o n s f o r one s t i m u l u s much l a r g e r t h a n f o r the o t h e r two) were r e c o r d e d i n t h i s study from s u b j e c t s who i n d i c a t e d t h a t t h e y "were not l o o k i n g forward" t o the s t i m u l u s and "knew i t would be a w f u l " , o r from s u b j e c t s who p r e s e n t e d a s t a r t l e r e a c t i o n ( S u b j e c t 1 PT, and S u b j e c t 9 TOBN i n F i g u r e 6; and S u b j e c t 1 TOBN i n F i g u r e 7). Djupesland(1964, 1965) has r e p o r t e d t h a t the middle e a r muscles may c o n t r a c t i n a n t i c i p a t i o n o f a l o u d s t i m u l u s and t h a t the t e n s o r tympani muscle w i l l c o n t r a c t w i t h p r e s e n t a t i o n o f a l o u d , u n p l e a s a n t s t i m u l u s e s p e c i a l l y i f t h a t s t i m u l u s i s unexpected. The l a r g e i n d i v i d u a l c o n t r a c t i o n s n o t e d i n t h i s study may r e p r e s e n t t e n s o r c o n t r a c t i o n i n a d d i t i o n t o normal s t a p e d i u s c o n t r a c t i o n . I t i s p o s s i b l e t h a t the n o i s e exposure h i s t o r y o f a s u b j e c t c o u l d a f f e c t the s t r e n g t h o f muscle c o n t r a c t i o n . I f , f o r example, a s u b j e c t was exposed t o n o i s e d u r i n g the day of t e s t i n g , muscle response would p r o b a b l y be s m a l l s i n c e i t may be assumed t h a t the system i s a l r e a d y i n a s t a t e o f f a t i g u e . Such a sequence o f even t s , was noted on one o c c a s i o n , f o r one s u b j e c t . That i s , a f t e r working i n a n o i s y environment d u r i n g the day, minimal changes i n impedance were found i n response to a c o u s t i c s t i m u l a t i o n ; but i n the absence of a n o i s y environment f o r 24 hours p r e c e d i n g t e s t i n g , muscle response was of normal s i z e . E f f e c t s of a t t e n t i o n , m o t i v a t i o n , and g e n e r a l body f a t i g u e on the a c o u s t i c r e f l e x are not known at p r e s e n t ; but these f a c t o r s c ould a f f e c t the s i z e of muscle response. Analyses of data f o r both groups of s u b j e c t s r e v e a l e d no s t a t i 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 s i n maximum d e f l e c t i o n f o r s t i m u l a t i o n w i t h PT, TOBN, and OBN. For s t i m u l a t i o n w i t h 1000 and 4000 Hz octave band n o i s e s , p r e s e n t e d at 105 dB SPL, Brasher et al(1970) a l s o found s i m i l a r degrees of c o n t r a c t i o n . On the ot h e r hand, Djupesland et al(1966) r e p o r t e d l a r g e r c o n t r a c t i o n s f o r t o n a l s t i m u l a t i o n of low frequency, than f o r t o n a l s t i m u l a t i o n of h i g h frequency, when s u b j e c t s were presented w i t h s t i m u l i at the same i n t e n s i t y r e l a t i v e t o r e f l e x t h r e s h o l d . Although the s i z e of the maximum impedance change f o r both low and h i g h frequency tones was the same, t h i s maximum change occurred at a h i g h e r SL f o r h i g h frequency t o n e s ( a p p r o x i m a t e l y 28 dB SL) than f o r low frequency t o n e s ( a p p r o x i m a t e l y 18 dB S L ) . Since no s i g n i f i c a n t d i f f e r e n c e s were found between e i t h e r pure tones and no i s e i n the present i n v e s t i g a t i o n or between low and h i g h frequency n o i s e i n Brasher et a l ' s study, i t c o u l d be hypothesized t h a t the i n t e n s i t y of the s t i m u l i used was such t h a t the muscles were i n t e t a n u s . -65-In o t h e r words, the s i z e o f c o n t r a c t i o n was s i m i l a r f o r the d i f f e r e n t s t i m u l i because the muscles were maximally c o n t r a c t e d . R e s u l t s r e p o r t e d by D j u p e s l a n d e t a l do n o t n e c e s s a r i l y r e f u t e t h i s h y p o t h e s i s . The i n t e n s i t y ( i n SPL) which produced maximum impedance changes f o r the d i f f e r e n t t o n e s , c o u l d have been s i m i l a r f o r i n d i v i d u a l s u b j e c t s ; but t h i s SPL cannot be determined s i n c e the d a t a p r e s e n t e d r e p r e s e n t s a mean v a l u e f o r 20 s u b j e c t s . I t would be o f i n t e r e s t t o determine the SPL and SL, f o r v a r i o u s pure t o n e s and n o i s e , which might produce s i m i l a r and maximum c o n t r a c t i o n o f the muscles. Such an i n v e s t i g a t i o n would enable, comparison of. r e s u l t s from v a r i o u s s t u d i e s , and u n d o ubtedly t h e s e r e s u l t s would add t o p r e s e n t knowledge o f the a c o u s t i c r e f l e x . As r e p o r t e d above, middle e a r muscle a c t i v i t y d e c r e a s e d , i . e . , the muscles r e l a x e d , p r o g r e s s i v e l y d u r i n g s t i m u l a t i o n w i t h pure t o n e s and n o i s e ; t h i s f i n d i n g i s i n agreement w i t h o t h e r s t u d i e s ( D a l l o s , 1964; D j u p e s l a n d e t a l , 1966; Kobrak e t a l , 1941; McBay, 1971). I t has been g e n e r a l l y assumed t h a t t h i s r e l a x a t i o n of the muscles i s due t o a d a p t a t i o n i n the e a r ( K r y t e r , 1970; Metz, 1951; M i l l e r , 1961), and t h a t a d a p t a t i o n " i s p r o b a b l y a c e n t r a l phenomenon(at l e a s t c e n t r a l to the h a i r c e l l s ) " ( W a r d , 1966, p. 484), i . e . , a d a p t a t i o n i s concerned w i t h the a c t i v i t y o f n e r v e s . As e a r l y as 1955, D e r b y s h i r e and D a v i s r e c o r d e d e l e c t r i c a l a c t i v i t y from the a u d i t o r y nerve of the c a t and r e p o r t e d t h a t a c t i o n p o t e n t i a l s d e c r e a s e d i n s i z e d u r i n g -bb-the f i r s t seven minutes of continuous pure tone s t i m u l a t i o n . Seven to t e n minutes a f t e r onset of s t i m u l a t i o n , D erbyshire and Davis r e p o r t e d t h a t the a c t i o n p o t e n t i a l s reached a steady l e v e l . Subsequent r e s e a r c h a l s o demonstrated a decrease i n the response of the a u d i t o r y nerve d u r i n g s u s t a i n e d s t i m u l a t i o n ( D a y a l , 1972; Galambos and D a v i s , 1943). I n 1970, E l l i o t t and E r a s e r r e p o r t e d t h a t n e u r a l responses decreased r a p i d l y and reached a s t a b l e l e v e l a f t e r t h r e e minutes of s t i m u l a t i o n . I t should be noted, however, t h a t i n 1963 S t a r r and L i v i n g s t o n recorded e l e c t r i c a l a c t i v i t y from v a r i o u s p l a c e s along the a u d i t o r y pathway i n c a t s and r e p o r t e d t h a t a c t i v i t y from the round window to i n f e r i o r c o l l i c u l u s i n c r e a s e d d u r i n g s t i m u l a t i o n and reached a s t a b l e l e v e l approximately on e - h a l f hour a f t e r onset of s t i m u l a t i o n . I n 1963, Garmel and S t a r r recorded EMG a c t i v i t y from the middle ear muscles and e l e c t r i c a l a c t i v i t y from the a u d i t o r y pathway d u r i n g two hours of s t i m u l a t i o n w i t h broad spectrum white n o i s e at 85 dB SPL. Carmel and S t a r r found an abrupt r i s e i n EMG a c t i v i t y at onset of s t i m u l a t i o n , f o l l o w e d by a r a p i d decrease i n a c t i v i t y d u r i n g the f i r s t few minutes, and a g r a d u a l decrease d u r i n g the subsequent 30 to 90 minutes of s t i m u l a t i o n . In agreement w i t h the f i n d i n g s of S t a r r and L i v i n g s t o n (1963), Carmel and S t a r r r e p o r t e d an i n c r e a s e i n e l e c t r i c a l a c t i v i t y along the a u d i t o r y pathway which m i r r o r e d EMG a c t i v i t y . Carmel and S t a r r concluded: -by-" R e s u l t s i n d i c a t e t h a t m i d d l e - e a r muscle a c t i v i t i e s a re not s o l e l y determined by the p h y s i c a l c h a r a c t e r i s t i c s o f sound s t i m u l i but r a t h e r they appear t o be governed by a wide v a r i e t y o f dynamic c e n t r a l nervous system p r o c e s s e s . " (p. 6-14) The s t u d i e s r e p o r t e d thus f a r , suggest t h a t a t l e a s t two f a c t o r s , i . e . , a d a p t a t i o n and c e n t r a l mechanisms, are i n v o l v e d i n the dec r e a s e i n middle ear muscle a c t i v i t y d u r i n g p r o l o n g e d s t i m u l a t i o n . C e n t r a l mechanisms might be r e s p o n s i b l e f o r a c e r t a i n degree of r e l a x a t i o n i n the muscles, r e g a r d l e s s o f the a p p l i e d s t i m u l u s ; and a d a p t a t i o n , f o r a d i f f e r e n c e i n r a t e o f r e l a x a t i o n d u r i n g s t i m u l a t i o n w i t h pure tones and n o i s e . In the p r e s e n t study, i t was observed t h a t muscle a c t i v i t y d e c r e a s e d l e s s r a p i d l y ( i . e . , r e f l e x decay was s m a l l e r ) f o r n o i s e s t i m u l a t i o n t han f o r t o n a l s t i m u l a t i o n . Thus i t would appear t h a t d u r i n g n o i s e s t i m u l a t i o n , more motor u n i t s o f the muscle remained a c t i v e t h a n d u r i n g pure tone s t i m u l a t i o n . F o r such a c o n d i t i o n t o oc c u r , e l e c t r i c a l a c t i v i t y i n the a u d i t o r y pathway must be m a i n t a i n e d t o a g r e a t e r degree by n o i s e , t han by pure t o n e s . T h i s d i f f e r e n c e c o u l d p o s s i b l y be accounted f o r by the n a t u r e o f the two sounds. Pure t o n e s c o n s t a n t l y e x c i t e the same r e g i o n o f the b a s i l a r membrane; c o n s e q u e n t l y the same nerve f i b r e s are a c t i v a t e d d u r i n g the p e r i o d o f s t i m u l a t i o n . S i n c e n o i s e v a r i e s i n f r e q u e n c y and i n t e n s i t y , no s i n g l e r e g i o n of the b a s i l a r membrane i s c o n s t a n t l y e x c i t e d , i . e . , the e x c i t a t i o n p a t t e r n v a r i e s . I n d i v i d u a l f i b r e s are a c t i v a t e d at d i f f e r e n t times and f o r d i f f e r e n t -68-p e r i o d s of time , t h e r e f o r e the f i b r e s adapt more s l o w l y . With s u s t a i n e d a c t i v i t y i n the nerve f i b r e s , impulses t o the muscle are maintained and the muscle remains c o n t r a c t e d . An i n t e r e s t i n g d i f f e r e n c e between the two groups of s u b j e c t s i s i l l u s t r a t e d i n F i g u r e s 14 and 15- Muscle a c t i v i t y decreased l e s s r a p i d l y d u r i n g s t i m u l a t i o n w i t h a 7 0 0 Hz pure tone(Group I ) than d u r i n g s t i m u l a t i o n w i t h a 1400 Hz tone(Group I I ) . I t i s p o s s i b l e t h a t t h i s d i f f e r e n c e i n r a t e of r e f l e x decay c o u l d be a t t r i b u t e d t o d i f f e r e n c e s among s u b j e c t s . I t should be noted, however, t h a t r e f l e x decay was s i m i l a r f o r both groups d u r i n g n o i s e s t i m u l a t i o n . Wever (1949) has r e p o r t e d : "low tones are not s u b j e c t t o f a t i g u e , or o n l y when presented at e x t r a o r d i n a r y l e v e l s of i n t e n s i t y . " ( p . 326). D e f i n i t i v e c o n c l u s i o n s about the r a t e of r e f l e x decay d u r i n g s t i m u l a t i o n w i t h low and h i g h frequency pure tones cannot be drawn from t h i s study; although the r e s u l t s undoubtedly suggest p o s s i b l e d i f f e r e n c e s . I n order t o v e r i f y such a d i f f e r e n c e , the same group of s u b j e c t s would have t o be exposed to tones of v a r i o u s f r e q u e n c i e s . Conclusions B e a r i n g i n mind the l i m i t a t i o n s of t h i s study, the the f o l l o w i n g r e s u l t s are i n d i c a t e d : (a) Obtained t h r e s h o l d s f o r pure tones were l a r g e r than obtained t h r e s h o l d s f o r n o i s e . (b) Pure t o n e s , o n e - t h i r d octave band n o i s e and octave band n o i s e were seen to e l i c i t muscle c o n t r a c t i o n s of s i m i l a r s i z e when s t i m u l i were presented at 1-14 dB SPL. -69-(c) Muscle a c t i v i t y was seen to decrease during f i v e minutes of sti m u l a t i o n f o r a l l s t i m u l i . (d) Group I subjects demonstrated s i g n i f i c a n t l y more r e f l e x decay f o r st i m u l a t i o n with pure tone than fo r s t i m u l a t i o n with octave band noise; Group I I subjects demonstrated s i g n i f i c a n t l y more decay f o r s t i m u l a t i o n with pure tone than f o r stimulation with octave and one-third octave band noises. (e) Reflex decay was noted to be less f o r stimulation with a 700 Hz pure tone than f o r sti m u l a t i o n with a 1400 Hz pure tone, and was s i m i l a r f o r stimulation with 500 and 1000 Hz octave band noises and f o r stim u l a t i o n with 630 and 1250 Hz one-third octave band noises. S e l e c t e d B i b l i o g r a p h y Brasher, P. P., Co l e s , R. R. A., Elwood, M. A.,, and P e r r e s , H. M. (1970). "The I n f l u e n c e of Middle-Ear Muscle A c t i v i t y on A u d i t o r y Threshold S h i f t s Induced by Noise," Army P e r s o n n e l Research E s t a b l i s h m e n t Research Memorandum S/3, .Parnborough, U. K. Bruning, J . L., and K i n i t z , B.L. (1968). Computional Hand- book of S t a t i s t i c s ( S c o t t , Poresman and Company, Glenview, 111.), pp. 4-3-54. ^ Carmel, P. W., and S t a r r , A. (1963). " A c o u s t i c and Nonacoustic F a c t o r s M o d i f y i n g Middle-Ear Muscle A c t i v i t y i n Waking Cats," J . N e u r o p h y s i o l . 26, 598-616. D a l l o s , P.J. (1964). "Dynamics of the A c o u s t i c R e f l e x : Phenomenological Aspects," J . Acoust. Soc. Amer. 36, 2175-2183-D a y a l , V. S. (1972). "A Study of Crossed O l i v o c o c h l e a r Bundle on A d a p t a t i o n of A u d i t o r y A c t i o n P o t e n t i a l s , " Laryngoscope 82, 693-711. D e r b y s h i r e , A. J . , and Da v i s , H. (1935). "The A c t i o n P o t e n t i a l s of the A u d i t o r y Nerve," Amer. J . P h y s i o l . 113, 476-504. Deutsch, L. J . (1972). "The Threshold of the Stapedius R e f l e x f o r Pure Tone and Noise S t i m u l i , " A c t a O t o l a r y n g . ,74, 248-251. Djupesland, G. (1964). "Middle Ear Muscle R e f l e x e s E l i c i t e d by A c o u s t i c and Nonacoustic S t i m u l a t i o n , " A c t a O t o l a r y n g ( S t o c k ) S u p p l . 188, 287-292. Djupesland, G. (1965). "Electromyography of the Tympanic Muscles i n Man," I n t . Audio1. 4, 34-41. Djupesland, G., F l o t t o r p , G., and Winther, P. 0. (1966). "Size and D u r a t i o n of A c o u s t i c a l l y E l i c i t e d Impedance Changes i n Man," Act a O t o l a r y n g . ( S t o c k ) Suppl. 224, 220-228. E l l i o t t , D. N., and F r a s e r , W. (1970). "Fatigue and Ada p t a t i o n , " i n Foundations of Modern A u d i t o r y Theory, J . V. Tob i a s , Ed. (Academic, New Y o r k ) , V o l . I , Chap. 4. E u s t a c h i u s , B. (1564). Opuscula anatomica, V e n e t i i s , pp. 148-164. -70-- 7 1 -Feldman, A. S., and Z w i s l o c k i , J . ( 1 9 6 5 ) . " E f f e c t s of the Acoustic Reflex on the Impedance at the Eardrum," J . Speech. Hear. Res. 8, 2 1 3 - 2 2 2 . F i s c h , U., and Schulthess, G. v. ( 1 9 6 3 ) . "Electromyographic Studies on the Human Stapedial Muscle," Acta Otolaryng. 56, 287-297-F l e e r , R. (1962). "Protection Against Impulsive Noise by Voluntary Contraction of the Middle Ear Muscles," i n Middle Ear Punction Seminar, J . L. Fletcher, Ed. U. S. Army Med. Res. Lab., Rep., Ft . Knox, Ky., No. 5 7 6 . Fletcher, J . L. ( 1 9 6 1 ) . "TTS Following Prolonged Exposure to Acoustic Reflex E l i c i t i n g S t i m u l i , " J . Aud. Res. 1, 242-246. Fletcher, J . L. (1961). "Prolongation of the Action of the Acoustic Reflex," J . Aud. Res. 1, 3 0 6 - 3 1 0 . F l e t c h e r , J . L. (1962). "Reflex Response of Middle Ear Muscles: P r o t e c t i o n of the Ear from Noise," Sound 1, 1 7 - 2 3 . Fletcher, J . L., and Loeb, M. (1962). "The Influence of Diff e r e n t A c o u s t i c a l S t i m u l i on the Threshold of the Co n t r a l a t e r a l Ear: A Pos s i b l e Index of Attenuation of the Intratympanic Reflex," Acta Otolaryng. 5 4 , 3 3 - 3 7 . Gacek, R. R. ( 1 9 7 2 ) . "Neuroanatomy of the Auditory System," i n Foundations of Modern Auditory Theory, J . V. Tobias, Ed. (Academic, New York), V o l . I I , Chap. 6». Galambos, R"., and Davis, H. ( 1 9 4 3 ) . "The Response of Single Auditory-Nerve Fibers to Acoustic Stimulation," J . Neurophysiol. 6, 3 9 - 5 7 . Galambos, R., and Rupert, A. ( 1 9 5 9 ) . "Action of the Middle Ear Muscles i n Normal Cats," J . Acoust. Soc. Amer. 3 1 , 3 4 9 - 3 5 5 . Gjaevenes, K., and Sohoel, Th. (1966). "Reactivating the Acoustic Stapedius Muscle Reflex by Adding a Second Tone," Acta Otolaryng. 62, 213-216. Hoist, H. S., Ingelstedt, S., and Ortegren, U. ( 1 9 6 3 ) . "Ear Drum Movements Following Stimulation of the Middle Ear Muscles," Acta Otolaryng.(Stock) Suppl. 182, 7 3 - 8 9 . Hung, I. J . , and Dal l o s , P. ( 1 9 7 2 ) . "Study of the Acoustic Reflex i n Human Beings. I . Dynamic C h a r a c t e r i s t i c s , " J . Acoust. Soc. Amer. 5 2 , 1168-1180. J e p s e n , 0. (1965). " M i d d l e - E a r Muscle R e f l e x e s i n Man," i n Modern Developments i n A u d i o l o g y , J . J e r g e r , Ed. (Academic, New Y o r k ) , Chap. 67 Johansson, B., K y l i n , B., and Langfy, M. (1967). " A c o u s t i c R e f l e x as a T e s t of I n d i v i d u a l S u s c e p t i b i l i t y to N o i s e , " A c t a O t o l a r y n g . 64, 256-262. K l o c k h o f f , I . (1961). "Middle E a r Muscle R e f l e x e s i n Man," A c t a O t o l a r y n g . ( S t o c k ) S u p p l . 164, 1-92. Kobrak, H. G. (1959). The Mi d d l e E a r ( U n i v e r s i t y o f Chicago P r e s s , C h i c a g o ) . Kobrak, H. G., L i n d s a y , J . R., and Perlman, H. B. (1941). " E x p e r i m e n t a l O b s e r v a t i o n s on the Q u e s t i o n o f A u d i t o r y P a t i g u e , " Laryngoscope 51, 798-810. K r y t e r , K. D. (1970). The E f f e c t s o f Noise on Man (Academic, New Y o r k ) , Chap. 3. L i l l y , D. J . (1964). "Some P r o p e r t i e s o f the A c o u s t i c R e f l e x i n Man," J . A c o u s t . Soc. Amer. 36, 2007. Loeb, M., and P l e t c h e r , J . L. (1963). "Temporary T h r e s h o l d S h i f t i n S u c c e s s i v e S e s s i o n s f o r S u b j e c t s Exposed t o Continuous and P e r i o d i c I n t e r m i t t e n t N o i s e , " J . Aud. Res. 3, 213-220. L i i s c h e r , E . (1929). "Die P u n k t i o n des Musculus S t a p e d i u s beim Menschen," Z. H a l s . Nas. Ohren. h e i l k 23, 105-132. Mendelson, E. S. (1957). "A S e n s i t i v e Method f o r R e g i s t r a t i o n of Human I n t r a t y m p a n i c Muscle R e f l e x e s , " J . A p p l . P h y s i o l . 11, 499-502. Metz, 0. (1951). " S t u d i e s on the C o n t r a c t i o n o f the Tympanic Muscles as I n d i c a t e d by Changes i n the Impedance of the E a r , " A c t a O t o l a r y n g . 39, 397-405-McBay^ H. D. (1971). I n f l u e n c e o f P h o n a t i o n on H i g h - I n t e n s i t y  Sound T r a n s m i s s i o n i n the A u d i t o r y System (U n p u b l i s h e d Master's T h e s i s , U n i v e r s i t y of B r i t i s h Columbia). F i l l e r , A. R. (1958). " I n t r a - A u r a l Muscle C o n t r a c t i o n i n Man, Examined by Measuring A c o u s t i c Impedance of the E a r , " Laryngoscope 68, 48-62. M 0 l l e r , A. R. (1961). " C o n t r a c t i o n o f the M i d d l e - E a r Muscles i n Man," J . A c o u s t . Soc. Amer. 33, 1669-M i l l s , J . H., and L i l l y , D. J . (1969). "Some E f f e c t s o f the A c o u s t i c R e f l e x Upon TTS," J . Ac o u s t . Soc. Amer. 46, 80. -75-M i l l s , J . H., and L i l l y , D. J . (1971). "Temporary T h r e s h o l d S h i f t s P r oduced "by Pure Tones and by Noise i n the Absence o f an A c o u s t i c R e f l e x , " J . A c o u s t . Soc. Amer. 50, 1556-1558. Perlman, H. B. (1938). " H y p e r a c u s i s , " Ann. O t o l . R h i n . L a r y n g . 4-7, 947-953-Perlman, H. B., and Case, I . J . (1939). " L a t e n t P e r i o d o f the C r o s s e d S t a p e d i u s R e f l e x i n Man," Ann. O t o l . R h i n . L a r y n g . 48, 663-675. P o t t e r , A. B. (1936). " F u n c t i o n o f the S t a p e d i u s Muscle," Ann. O t o l . R h i n . L a r y n g . 45, 638-643. S t a r r , A., and L i v i n g s t o n , R. B. (1963). " L o n g - L a s t i n g Nervous System Responses t o P r o l o n g e d Sound S t i m u l a t i o n i n Waking C a t s , " J . N e u r o p h y s i o l . 26, 416-431. Smith, R. P., Loeb, M., F l e t c h e r , J . L., and Thomas, D. M. (1966). "The E f f e c t o f Moderate Doses o f Curare on C e r t a i n A u d i t o r y F u n c t i o n s , " A c t a O t o l a r y n g . 62, 101-108. T i e t z e , G. (1969). "Zum Zeitverhacttten des A k u s t i s c h e n R e f l e x e s b e i Reizung m it Dauertonen," A r c h . k l i n . exp. Ohr.-, Nas.- u. K e h l k . Heilk. ' 1 9 3 , 43-52. Towe, A. L. (1965). " A u d i t i o n and the A u d i t o r y Pathway," i n P h y s i o l o g y and B i o p h y s i c s , T. C. Ruch and H. D. P a t t o n , E d s . (V/. B. Saunders, P h i l a d e l p h i a ) , Chap. 18. V a r o l i u s , C. (1591). Anatomiae s i v e de r e s o l u t i o n e c o r p o r i s humani, l i b r i I I I , F r a n c o f u r t i . Ward, W. D. (1961). " S t u d i e s on the A u r a l R e f l e x . I . C o n t r a l a t e r a l Remote Masking as an I n d i c a t o r o f R e f l e x A c t i v i t y , " J . A c o u s t . Soc. Amer. 33, 1034-1045-Ward, W. D. (1962 a ) . " S t u d i e s on the A u r a l R e f l e x . I I . R e d u c t i o n o f Temporary T h r e s h o l d S h i f t from I n t e r m i t t e n t N o i s e by R e f l e x A c t i v i t y ; I m p l i c a t i o n s f o r Damage-Risk C r i t e r i a , " J . A c o u s t . Soc. Amer. 34, 234-241. Ward, W. D. (.1962 b ) . "Damage-Risk C r i t e r i a f o r L i n e S p e c t r a , " J . A c o u s t . Soc. Amer. 34, 1610-1619. Ward, W. D. (1963). " A u d i t o r y F a t i g u e and Masking," i n Modern Developments i n A u d i o l o g y , J . J e r g e r , Ed. (Academic, New Y o r k ) , Chap. 7» Ward, W. D. (1966). "Temporary T h r e s h o l d S h i f t i n Males and Females," J . Ac o u s t . Soc. Amer. 40, 478-485-Ward," V/. D. (1967). " F u r t h e r O b s e r v a t i o n s on C o n t r a l a t e r a l Remote Masking and R e l a t e d Phenomena," J . A c o u s t . Soc. Amer. 42, 593-600. Ward, W. D., G l o r i g , A., and S k l a r , D. L. (1959). "Temporary T h r e s h o l d S h i f t from Octave-Band N o i s e : A p p l i c a t i o n s t o Damage-Risk C r i t e r i a , " J . A c o u s t . Soc. Amer. 31, 522-528. Weiss, H. S., Mundie, J . R., C a s h i n , J . L., and S h i n a b a r g e r , E. W. (1962). "The Normal Human I n t r a - A u r a l Muscle R e f l e x i n Response t o Sound," A c t a O t o l a r y n g . 55, 505-515. Wever, E. G. (1949). Theory o f H e a r i n g (John Wiley & Sons, New Y o r k ) , pp. 319-326. Wever, E. G., and Lawrence, M. (1954). P h y s i o l o g i c a l A c o u s t i c s ( P r i n c e t o n U n i v e r s i t y P r e s s , P r i n c e t o n ) , p. 5« Winer, B. J . (1962). S t a t i s t i c a l P r i n c i p l e s i n E x p e r i m e n t a l  D e s i g n ( M c G r a w - H i l l , New Y o r k ) , Chap. 4. Woodbury, J . W., Gordon, A. M., and Conrad, J . T. (1965). "Muscle," i n P h y s i o l o g y and B i o p h y s i c s , T. C. Ruch and H. D. P a t t o n , Eds. (W. B. Saunders, P h i l a d e l p h i a ) , Chap. 5. Z e m l i n , W. R. (1968). Speech and H e a r i n g S c i e n c e ( P r e n t i c e -H a l l , Englewood C l i f f s , New J e r s e y ) . -75-A p p e n d i x  I n s t r u c t i o n s to the S u b j e c t s The purpose of t h i s t e s t i s to study some of the p r o p e r t i e s of the middle ear muscles. The t e s t w i l l l a s t approximately 15 minutes. T h i s rubber p l u g w i l l be i n s e r t e d i n t o your l e f t / r i g h t ear and w i l l remain t h e r e d u r i n g the e n t i r e t e s t . You w i l l hear a low frequency tone i n the ear w i t h the p l u g throughout the t e s t i n g . The t e s t s t i m u l u s w i l l be p r e s e n t e d through the earphone to your r i g h t / l e f t ear. For one minute you w i l l hear o n l y the low frequency tone. You w i l l hear the t e s t s t i m u l u s and low frequency tone f o r the next f i v e minutes; then the tone alone f o r two minutes. I w i l l warn you 1 0 seconds before the t e s t s t i m u l u s i s removed. P l e a s e r e f r a i n from coughing, yawning, b o d i l y movements, and e x c e s s i v e swallowing as these w i l l adverse a f f e c t the r e c o r d i n g . Do you have any questions? 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0101252/manifest

Comment

Related Items