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Acoustic Reflex Measures in Normal and Sensorineural

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Acoustic Reflex Measures in Normal and Sensorineural I no,36 ACOUSTIC REFLEX MEASURES IN NORMAL AND SENSORINEURAL HEARING-IMPAIRED EARS Bradley Carl Miller A Dissertation Submitted to the Graduate School of Bowling Green State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY August 1975 Approved by j^octoral Committee ’Advisor ii ABSTRACT Three temporal parameters of the acoustic reflex were compared in 30 normal and 15 sensorineural hearing- impaired subjects. Wide-band noise and octave-band noise centered at 500, 1000, 2000 and 4000 Hz were utilized as reflex producing stimuli. The sensorineura1 group demonstrated significantly longer reflex offset times than the normal group. Estimates of probabilities of a subject having a sensori­ neural hearing loss were calculated from the frequency distribution of the reflex durations and it was found that weighted decisions about their hearing could be made with a high degree of accuracy. 1X1 ACKNOWLEDGEMENTS I wish to express my sincere appreciation to Dr. Michael Doherty, who served actively as a member of my committee and as my minor area advisor. Thanks is also extended to Dr. George Herman and Dr. Raymond Tucker who served supportively as members of my committee. I will always appreciate the concerned help of Miss Barbara Price of the Toledo School District, without whose efforts this study would have been delayed several months. I feel a particular debt of gratitude toward my chairman, Dr. Herbert Greenberg, who has related to me as a teacher, advisor, colleague and friend. Academically, he more than anyone is responsible for making my graduate studies purposeful and rewarding. My greatest debt is unquestionably to my loving wife, Nancy, who has made many personal sacrifices, but has persevered as my most vigorous supporter throughout my personal and academic endeavors. Prayerful gratitude is humbly expressed for the abilities and blessings that enabled me to undertake and complete this study and degree. iv TABLE OF CONTENTS Page INTRODUCTION....................................... 1 REVIEW OF THE LITERATURE.......................... 3 Threshold and Suprathresh©Id Properties of the Acoustic Reflex.... .....«..*..... • • 3 Temporal Response Measures of the Acoustic Reflex.... .......... 4 Statement of the Problem.................. *7 METHOD............................................. 3 Subjects.... .......................... 3 Stimuli....................................... 9 Instrumentation.... ......................... 11 Test Procedure.............. 13 Response Analysis........................... 14 RESULTS.......... 15 Measurement Reliability.15 Reflex Amplitude Validity. ................... 15 Reflex Measurements...... 16 Estimate of Probabilities of Sensori­ neural Deficit.................. 13 DISCUSSION......................................... 22 Future Research............... 26 REFERENCES..................... 28 APPENDIX...... 31 V LIST OF TABLES Page Table 1. Mean Values and Standard Deviations of Acoustic Reflex Amplitude for Normal and Sensorineural Hearing-Impaired 16 Subjects.... ........................ ........ 2. Mean Values (msec) and Standard Devia­ tions of Acoustic Reflex Onset, Dura­ tion and Offset Responses for Normal and Sensorineural Hearing-Impaired Subjects Using Various Noise Bands...................... ................... 17 3. Estimates of Probabilities of Sensori­ neural Deficit.......... ............ 20 VI LIST OF FIGURES Page Figure — 1, Block Diagram of Equipment Used for Signal Presentation and Reflex Recording. ..................... ....... ....... 12 2. Distribution of Acoustic Reflex Dura­ tion for Nonna1 and Sensorineural Hearing-Impaired Subjects19 INTRODUCTION Even though researchers have been studying the acoustic reflex for almost a century many questions about this middle ear muscle reflex still remain un­ resolved (Dallos, 1973). Recent advances in equipment technology have en­ abled investigators to study many different properties of the acoustic reflex (Holst et al., 1963). The primary concern of researchers has been the measurement of re­ flex threshold, although there have been some investi­ gations into other reflex parameters (Anderson et al,, 1970j Alberti, 1972j Norris et al., 1974a, 1974bj Colletti, 1974). There have been three main types of other reflex measurements discussed in the litera­ ture. The most commonly studied has been that of re­ flex onset where the investigators were concerned with the time interval between stimulus onset and reflex onset (Metz, 1946 j Klocfchoff, 1961> Dallos, 1964). However, more recently researchers have been studying reflex adaptation and reflex offset. Anderson et al. (1970) found that they were able to distinguish between normal and VIII nerve lesion ears by measuring the re­ flex adaptation to a stimulus of 10 seconds duration. Norris et al. (1974a) and Colletti (1974) found they were able to differentiate normal from sensorineural 2 hearing-impaired individuals by observing reflex offset to a short duration pulsed stimulus. The most recent study to date (Norris et al., 1974b) examined several reflex parameters in normal and sensorineural hearing- impaired populations. They found differences between these two populations in reflex offset but not in re­ flex onset. However, only a 1 KHz pure tone of 250 msec duration was used as the stimulus to elicit the acoustic reflex. A more extensive stimulus plan should certainly be used to study and compare the temporal characteristics of the acoustic reflex in these groups. This study is therefore designed to assess several temporal parameters of the acoustic reflex of normal and sensorineural hearing-impaired ears using various octave bands of white noise. 3 REVIEW OF THE LITERATURE This literature review includes research in­ vestigations in two major areas: (1) threshold and suprathreshold properties of the acoustic reflex, and (2) temporal response measures of the acoustic reflex, i.e., reflex onset, reflex adaptation and reflex offset. Threshold and Suprathreshold Properties of the Acoustic Reflex The acoustic reflex (AR) in man has been studied using acoustic impedance techniques since the early l930*s. A thorough history and description of the acoustic re­ flex is presented in Moller (1972) and Jepsen (1963). Deutsch (1972) measured the acoustic reflex in 30 normal hearing young adults. Pure tones of 250 Hz, 2 KHz, and bursts of narrow-band noise centered at 2 KHz and 4 KHz were employed to elicit an AR. He found that the mean reflex threshold for pure tones was 81 dBSL and the mean for noise was 62 dBSL. He reported that noise stimuli elicited a more stable reflex than did pure tones. Other investigators (Metz, 1946 > Djupes- land, 1964j Danaher and Pickett, 1974) also reported that noise stimuli were considerably more effective than pure tones in eliciting the AR in normal and sensorineural ears. 4 Very little information is available with regard to the measurement of reflex thresholds on a sensori­ neural hearing-impaired population. Keating et al. (1972) used an audiometer with a maximum output of 110 dBHL to investigate the AR thresholds of students at a school for the deaf. They examined 133 children classified as otologically normal and obtained reflex thresholds on only 22 of these subjects. Danaher and Pickett (1974) studied 15 congenitally deaf students with marked-to-severe sensorineural hearing-impair­ ments. They employed a signal source with maximum output of 130 dBSPL and found the range of reflex thresholds to be from 100 to 130 dBSPL. They suggested the use of broad-band noise rather than pure tones in eliciting the reflex since pure tones were not as effective a stimulus for this population. Since the AR was elicited at lower levels with a noise stimulus, fewer cross-over problems were encountered. Temporal Response Measures of the Acoustic Reflex Reflex Onset Reflex onset refers to the time interval between stimulus onset and initial reflex onset. For a given sound pressure level, the reflex onset is shorter for noise than for pure tones around l KHz, and longest 5 for pure tones lower than 300 Hz (Hung and Dallos, 1972). This study also reported that the reflex onset was shortened by increasing the stimulus intensity. Dallos (1964) and Djupesland (1964) reported similar findings, although Djupesland observed a more rapid change in impedance for low frequency stimuli than for high fre­ quency stimuli when the stimulus intensity was increased. Norris et al. (1974b) observed slight differences in reflex onset between a normal and a sensorineural hearing- impaired group, however, no significant differences were found. Reflex Adaptation Dallos (1964) pointed out that at high stimulus levels a sustained muscle reflex is observed due to the involvement of many neurons; at medium levels the re­ sponse rapidly achieves an initial peak and then steadily decreases; and, near threshold it peaks and then is rapidly extinguished. He observed these re­ sponses when stimuli of up to 120 seconds in duration were employed. Anderson et al. (1970) studied this adaptation phenomenon of the acoustic reflex with normal and VIII nerve lesion subjects. They used a 10 second stimulus at 10 dB above their reflex thres­ hold, Their results showed that VIII nerve lesion 6 subjects have much faster adaptation than the normals, even in cases when they have normal audiometric thresholds. Together, these two studies suggested that a reflex elicited by a stimulus above the AR threshold and of sufficient duration (at least 3 seconds) is influenced by neural
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