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Reflex modulation: A new method of measuring hearing in children
International Journal of Pediatric Otorhinolaryngology, @ Elsevier/North-Holland Biomedical Press
3 (1981) 79--84
79
REFLEX MODULATION: A NEW METHOD OF MEASURING HEARING IN CHILDREN
LEVI A. REITER Department of Otolaryngology. Division of Audiology, University of Kansas Medical Center, School of Health Sciences and Hospital, 39th and Rainbow Blvd., Kansas City, Kans. 66103 (U.S.A.) (Received July 29th, 1980) (Accepted September 2nd, 1980)
SUMMARY
The term reflex modulation (RM) as used here refers to an auditorially induced modification in the magnitude of a cutaneous reflex. The audiometric potential of RM was examined in two children, while they enjoyed viewing silent cartoons. Eyeblink reflexes elicited by an airpuff were reduced in amplitude or “inhibited” by a variety of audible tones presented 100 msec prior to reflex elicitation. The amount of relative blink inhibition was directly related to the intensity of the tones. The weakest tone intensities which produced reliable blink-inhibition were usually about 10 dB above voluntary threshold. Implications for testing the difficult-to-test are discussed.
INTRODUCTION
Reflex modulation (RM) refers to a general class of phenomena in which a weak, but suprathreshold, auditory, visual or tactile pre-stimulus can alter (by facilitation or inhibition) the normal or control magnitude of an elicited reflex. The principle of RM has been applied recently to the field of objective clinical audiometry with the following rationale. If the presentation of a pure tone which precedes an airpuff-elicited eyeblink is shown to inhibit the magnitude of the blink reflex, then that tone can be said to have been processed auditorially. Reiter demonstrated the audiometric potential of RM in both normal hearing [ 41 and hearing-impaired adults [ 31 while the subjects watched silent films of read material of their choice. Despite the absence of sedation or even instructions to attend to stimuli, pure tones as low as lo-15 dB sensa-
80
tion level (SL) inhibited the eyeblink reflex to an airpuff, indicating objectively the presence of hearing at that level. More recently a high degree of threshold sensitivity for RM was shown in patients manifesting pseudohypacusis and other psychological disorders [ 71. Because the pediatric population is generally the least attentive and most difficult to control behaviorally, it stands to benefit most from an objective test, especially one which is minimally sensitive to behavioral and attentional variables. The present study therefore extended the eyeblink-inhibition paradigm to children and assessed the sensitivity and general viability of a clinical RM test for patients of the pediatric group. Silent, color TV cartoons were shown during testing and RM results were compared to voluntary audiometric data. GENERAL
METHODS
Subjects
The cases of two whose audiometric nique. These were Hearing and Speech
hearing-impaired children (9 and 11 years) are presented configurations were studied in detail by the RM techreferred to the experiment by their audiologist at the Center of Rochester.
Apparatus and procedure The subjects were tested individually in a double-walled Industrial Acoustics Company chamber while seated comfortably and watching cartoons. Eyeblinks were recorded with standard electronystagmographic silver/ silver chloride surface electrodes taped 5 mm above and below the right orbit, with a ground electrode placed at mid-forehead 5 mm below the hairline. Eyeblinks were amplified on a Beckman Dynographic Recorder (Type RS), and displayed graphically via a Tektronix storage oscilloscope (5103N) from which blink amplitude could be measured in mm of beam deflection. Blinks were elicited with an airpuff, 70 msec in duration, at 0.5 lb/sq.in. (psi), which was delivered 5 mm lateral to the right eye. A lightweight velcro head strap was used to maintain the position of a plastic tube which delivered the airpuff. Compressed air was supplied by a central air compression unit and directed through a calibrated self-bleeding valve which was attached to an electrically operated air release solenoid. A 10 psi pressure meter was situated between the self-bleeding valve and solenoid, and gave a continuous pressure reading. Airpuff onset and duration were regulated by a solid state 1000 msec timer controlling the air release solenoid. The acoustic stimuli were pure tones, 70 msec in duration, with a 5 msec rise-decay time, presented via a TDH-39 earphone in a MX-41/AR cushion. Tones were chosen for each case which would reflect significant aspects of a subject’s voluntary audiometric configuration. Tonal stimuli were generated by a Hewlett Packard oscillator (241A), varied in intensity via a Daven attenuation network (Type VT 795 G), and shaped by an electronic switch before being fed to the earphone. Signal
81
intensities were measured and calibrated with a General Radio sound level meter (1561) through a General Radio earphone coupler (1560-P83). Tonal duration (70 msec) and a 100 msec tone-puff interval (onset to onset, the interval shown by Reiter and Ison [ 51 to inhibit the blink maximally) were controlled by a series of 1000 msec solid state timers. The subjects were exposed to two types of trials during the experiment: a control (C) in which the ah-puff alone was presented, and an inhibitory or pre-pulse trial (P) in which the initiation of one of several test tones preceded the airpuff by 100 msec. The C and several inhibitory P-trials were presented in quasi-random order per the method of constant stimuli. One C-trial was presented for every two to three P-trials. Subjects were given 5 full minutes in which to adapt to the head-gear and environment before testing. They were then screened for voluntary threshold at 0.25, 0.5, 1, 4, and 8 kHz. Four airpuffs were then given both to calibrate the eyeblink recording equipment and to familiarize the children with the reflex eliciting stimulus. Following this the children were instructed to “enjoy the cartoons”, the TV set was turned on, and the experiment proper was begun. The experimenter and the control and recording apparatus were all situated outside the double-walled Industrial Acoustics Company chamber. Verbal contact was possible between subject and experimenter through an intercom, and a closed circuit television system enabled the experimenter to view the subject and thus withhold trials during yawns, spontaneous blinks and position shifts. The time interval between trials (ITI) ranged from 15 to 20 set when children were sitting relatively still; otherwise it was occasionally as long as 1 or 2 min. The test session for testing three frequencies lasted 40 min. CASE
1
L.S. was a g-year-old girl with a moderate bilateral symmetrical sensorineural hearing loss showing a deep saucer-shaped configuration. Her right ear voluntary thresholds for 0.25, 1 and 8 kHz were 40, 88, and 20 dB (SPL), respectively. Reflex modulation was conducted at 0.25, 1 and 8 kHz, presented at 90,60 and 30 dB (SPL). The results for L.S. are plotted in “reverse” mm eyeblink amplitude in Fig. 1. Confidence intervals (P = 0.05, t-test) were constructed about each plotted point for visually apparent estimates of the reliability of inhibition produced by each tone. If a confidence interval does not overlap the control arrow (on the left) then that tone was reliably inhibitory and can thus be said to have been detected. Voluntary thresholds are given below the figure, and all dB values are re SPL. The saucer-shaped pattern described in the audiologist’s report is strikingly apparent in the configuration of eyeblink amplitudes noted in Fig. 1. Moreover, the reliability of this shape was supported by the presence of a
82
.25 I FREQUENCY
8 ( kHZ 1
Fig. 1. Mean reflex amplitude for a hearing-impaired child, L.S., as a function of the frequency and intensity of S1. Confidence intervals are presented with each point. Voluntary thresholds for L.S. were: 0.25 kHz = 40 dB, 1 kHz = 88 dB, 8 kHz = 20 dB, all re SPL.
strong quadratic orthogonal trend (F = 68.31, df = 1, 8, P < 0.001). The relatively greater inhibition produced at 8 kHz than at 1 kHz (and to a lesser extent 0.25 kHz) is also a reliable observation (supported by a linear trend across frequency, F = 7.35, df = 1, 8, P = 0.027), and accurately reflects the configuration of voluntary thresholds. Reflex modulation’s ability to follow the relative physical intensity of audible acoustical stimuli is apparent in the proper ordinal positions of the 90, 60 and 30 dB curves (for a linear trend for SPL, F = 15.31, df = 1,8, P = 0.004). Thus, as was true for hearingimpaired adults [ 31, the configurations present in the RM curves are reliable indicators of the relative extent and location of conventionally measured hearing losses. In examining the confidence intervals about each point, RMs sensitivity to stimuli at lo-15 dB SL becomes evident; however, the adverse effects of the high variability in behavior noted while testing L.S. also emerge. For example, there is a widening of the confidence intervals and a consequent decrease in the sensitivity of RM. Thus, while the 60 dB (SPL), 0.25 kHz pip was 20 dB above voluntary threshold, the extremely broad confidence interval surrounding that point overlapped the C level (indicated by an arrow at the ordinate), and thus prevented its reliable detection by RM. While the same discrepancy seems to be present at 30 dB for the 8 kHz stimulus, a more precise, correlated t-test between inhibited and corresponding C eyeblink amplitudes revealed inhibition by that acoustical stimulus to be reliable (t = 2.09, df = 8, P < 0.05, one-tailed). Except for the 0.25 kHz stimulus at 60 dB, RM was still sensitive to stimuli at about 10 dB above their voluntary threshold levels. CASE 2
K.Z. was an 11-year-old
boy with mild bilateral
sensorineural
hearing loss.
83
FREQUENCY
( kHZ )
Fig. 2. Mean reflex amplitude for a hearing-impaired child, K.Z., as a function of the frequency and intensity of S1. Confidence intervals are presented with each point. The uninhibited control level is indicated by an arrow at the ordinate. Voluntary thresholds for K.Z. were: 0.25 kHz = 49 dB, 1 kHz = 40 dB, 4 kHz = 55 dB, all re SPL.
His voluntary thresholds obtained about 5 min prior to the experiment for 0.25,1 and 4 kHz were 49,40 and 55 dB (SPL), respectively. For RM, 0.25, 1 and 4 kHz were presented to the right ear at 90,60 and 30 dB (SPL). Fig. 2 shows the results for K.Z. plotted again in “reversed” mm eyeblink amplitude. Voluntary thresholds (re SPL) are listed beneath the figure. The configuration of data points shown in Fig. 2 is characteristic of the generally shallow downward sloping pattern of K.Z.‘s voluntary audiogram. There was no main effect for frequency in the data. The tendency for RM to follow the relative intensities of the acoustical stimuli was supported statistically by a linear effect for SPL (F = 9.38, df = 1,8, P = 0.016). The greater spacing of inhibited blink amplitudes between 90 and 60 dB than between 60 and 30 dB (SPL), reflects the relative closeness of the three voluntary thresholds to 60 dB. This differential spacing is reliable and is described statistically by a quadratic trend for SPL (F = 6.35, df = 1, 8, P = 0.036). Thus, the RM pattern obtained during television viewing revealed the topographical characteristics of the underlying audiometric function. An individual points analysis done on the basis of the confidence intervals for K.Z. shows that RM was consistently sensitive to the presence of acoustical stimuli at 10 dB above voluntary threshold. All tones presented at 90 dB (SPL) were both audible on the voluntary measure and inhibitory on the reflex measure. At 60 dB the same is true for 0.25 kHz, which was only 11 dB above threshold, and for 1 kHz. Although 4 kHz was also audible it was but 5 dB above threshold at 60 dB, and was thus not reliably inhibitory. Finally, at 30 dB (SPL) the tones were neither audible nor inhibitory with respect to the reflex. CONCLUSIONS
Reflex modulation
was studied in two hearing-impaired children. Evi-
a4
dence of hearing of the test signals was provided by RM as low as lo-15 dB SL. In addition to this, the relative sensory impact or ‘loudness’ of each stimulus was represented objectively by the relative magnitude of reflex inhibition. This latter potentiality was shown by Reiter and Ison [6] to enable the charting of loudness growth and, in pathological cases, to permit diagnosis of loudness recruitment to be made. It is interesting that these results were obtained with RM even though subjects during testing were engaged in a distracting activity, e.g. watching television. The fact that so little in the way of voluntary cooperation or attention to the stimuli was required for proper evaluation by RM, encourages the prospects of its being used successfully as an audiometric test for the more ‘difficult-to-test’ child or adult. It is worth noting that reliable RM results have recently been observed in cases of functional hearing disorder [ 71 and in infants [ 21. Of further significance is that RM sensitivity was about equivalent (at lo-15 dB SL) for low, e.g. 0.25 kHz, as well as high frequency auditory stimulation, e.g. 4 kHz. Since the audiometric sensitivity of the other current objective techniques, e.g. brainstem audiometry and electrocochleography, drops off sharply below about 2 kHz [ 11, the good low frequency sensitivity of RM is a rather unique and important attribute. ACKNOWLEDGEMENTS
This research was done in partial fulfillment of the degree of Doctor of Philosophy awarded by the University of Rochester, and was supported by research grants from the National Institute of Neurological and Communication and Disorders and Stroke, NS 12443 and 1 F32 NS05918-01. The author would like to thank Drs. Cornelius P. Goetzinger and James R. Ison for their advise and encouragement. REFERENCES 1 Davis, J., Principles of electric response audiometry, Ann. Otol. (St. Louis) 28, Suppl. (1976) 85. 2 Marsh, R.R., Hoffman, H.S. and Stitt, C.L., Reflex inhibition audiometry: a new technique, Acta oto-laryng. (Stockh.), 85 (1978) 336-341. 3 Reiter, L.A., Development and Evaluation of Reflex Modulation as an Objective Audiometric Procedure. Doctoral Dissertation, University of Rochester, 1977, Dissert. Abstr., 24 (1978). 4 Reiter, L.A., Experiments re: the clinical application of reflex modulation audiometry, J. Speech Hear. Res., in press. 5 Reiter, L.A. and Ison, J.R., Inhibition of the human eyeblink reflex: evaluation of the sensitivity of the Wendt-Yerkes method for threshold detection, J. exp. Psychol., 3 (1977) 325-336. 6 Reiter, L.A. and Ison, J.R., Reflex modulation and loudness recruitment, J. audit. Res., in press. 7 Reiter, L.A., Goetzinger, C.P. and Press, S.R., Reflex modulation audiometry: a hearing test for the difficult-to-test, J. Speech Hear. Dis., in press.
3 (1981) 79--84
79
REFLEX MODULATION: A NEW METHOD OF MEASURING HEARING IN CHILDREN
LEVI A. REITER Department of Otolaryngology. Division of Audiology, University of Kansas Medical Center, School of Health Sciences and Hospital, 39th and Rainbow Blvd., Kansas City, Kans. 66103 (U.S.A.) (Received July 29th, 1980) (Accepted September 2nd, 1980)
SUMMARY
The term reflex modulation (RM) as used here refers to an auditorially induced modification in the magnitude of a cutaneous reflex. The audiometric potential of RM was examined in two children, while they enjoyed viewing silent cartoons. Eyeblink reflexes elicited by an airpuff were reduced in amplitude or “inhibited” by a variety of audible tones presented 100 msec prior to reflex elicitation. The amount of relative blink inhibition was directly related to the intensity of the tones. The weakest tone intensities which produced reliable blink-inhibition were usually about 10 dB above voluntary threshold. Implications for testing the difficult-to-test are discussed.
INTRODUCTION
Reflex modulation (RM) refers to a general class of phenomena in which a weak, but suprathreshold, auditory, visual or tactile pre-stimulus can alter (by facilitation or inhibition) the normal or control magnitude of an elicited reflex. The principle of RM has been applied recently to the field of objective clinical audiometry with the following rationale. If the presentation of a pure tone which precedes an airpuff-elicited eyeblink is shown to inhibit the magnitude of the blink reflex, then that tone can be said to have been processed auditorially. Reiter demonstrated the audiometric potential of RM in both normal hearing [ 41 and hearing-impaired adults [ 31 while the subjects watched silent films of read material of their choice. Despite the absence of sedation or even instructions to attend to stimuli, pure tones as low as lo-15 dB sensa-
80
tion level (SL) inhibited the eyeblink reflex to an airpuff, indicating objectively the presence of hearing at that level. More recently a high degree of threshold sensitivity for RM was shown in patients manifesting pseudohypacusis and other psychological disorders [ 71. Because the pediatric population is generally the least attentive and most difficult to control behaviorally, it stands to benefit most from an objective test, especially one which is minimally sensitive to behavioral and attentional variables. The present study therefore extended the eyeblink-inhibition paradigm to children and assessed the sensitivity and general viability of a clinical RM test for patients of the pediatric group. Silent, color TV cartoons were shown during testing and RM results were compared to voluntary audiometric data. GENERAL
METHODS
Subjects
The cases of two whose audiometric nique. These were Hearing and Speech
hearing-impaired children (9 and 11 years) are presented configurations were studied in detail by the RM techreferred to the experiment by their audiologist at the Center of Rochester.
Apparatus and procedure The subjects were tested individually in a double-walled Industrial Acoustics Company chamber while seated comfortably and watching cartoons. Eyeblinks were recorded with standard electronystagmographic silver/ silver chloride surface electrodes taped 5 mm above and below the right orbit, with a ground electrode placed at mid-forehead 5 mm below the hairline. Eyeblinks were amplified on a Beckman Dynographic Recorder (Type RS), and displayed graphically via a Tektronix storage oscilloscope (5103N) from which blink amplitude could be measured in mm of beam deflection. Blinks were elicited with an airpuff, 70 msec in duration, at 0.5 lb/sq.in. (psi), which was delivered 5 mm lateral to the right eye. A lightweight velcro head strap was used to maintain the position of a plastic tube which delivered the airpuff. Compressed air was supplied by a central air compression unit and directed through a calibrated self-bleeding valve which was attached to an electrically operated air release solenoid. A 10 psi pressure meter was situated between the self-bleeding valve and solenoid, and gave a continuous pressure reading. Airpuff onset and duration were regulated by a solid state 1000 msec timer controlling the air release solenoid. The acoustic stimuli were pure tones, 70 msec in duration, with a 5 msec rise-decay time, presented via a TDH-39 earphone in a MX-41/AR cushion. Tones were chosen for each case which would reflect significant aspects of a subject’s voluntary audiometric configuration. Tonal stimuli were generated by a Hewlett Packard oscillator (241A), varied in intensity via a Daven attenuation network (Type VT 795 G), and shaped by an electronic switch before being fed to the earphone. Signal
81
intensities were measured and calibrated with a General Radio sound level meter (1561) through a General Radio earphone coupler (1560-P83). Tonal duration (70 msec) and a 100 msec tone-puff interval (onset to onset, the interval shown by Reiter and Ison [ 51 to inhibit the blink maximally) were controlled by a series of 1000 msec solid state timers. The subjects were exposed to two types of trials during the experiment: a control (C) in which the ah-puff alone was presented, and an inhibitory or pre-pulse trial (P) in which the initiation of one of several test tones preceded the airpuff by 100 msec. The C and several inhibitory P-trials were presented in quasi-random order per the method of constant stimuli. One C-trial was presented for every two to three P-trials. Subjects were given 5 full minutes in which to adapt to the head-gear and environment before testing. They were then screened for voluntary threshold at 0.25, 0.5, 1, 4, and 8 kHz. Four airpuffs were then given both to calibrate the eyeblink recording equipment and to familiarize the children with the reflex eliciting stimulus. Following this the children were instructed to “enjoy the cartoons”, the TV set was turned on, and the experiment proper was begun. The experimenter and the control and recording apparatus were all situated outside the double-walled Industrial Acoustics Company chamber. Verbal contact was possible between subject and experimenter through an intercom, and a closed circuit television system enabled the experimenter to view the subject and thus withhold trials during yawns, spontaneous blinks and position shifts. The time interval between trials (ITI) ranged from 15 to 20 set when children were sitting relatively still; otherwise it was occasionally as long as 1 or 2 min. The test session for testing three frequencies lasted 40 min. CASE
1
L.S. was a g-year-old girl with a moderate bilateral symmetrical sensorineural hearing loss showing a deep saucer-shaped configuration. Her right ear voluntary thresholds for 0.25, 1 and 8 kHz were 40, 88, and 20 dB (SPL), respectively. Reflex modulation was conducted at 0.25, 1 and 8 kHz, presented at 90,60 and 30 dB (SPL). The results for L.S. are plotted in “reverse” mm eyeblink amplitude in Fig. 1. Confidence intervals (P = 0.05, t-test) were constructed about each plotted point for visually apparent estimates of the reliability of inhibition produced by each tone. If a confidence interval does not overlap the control arrow (on the left) then that tone was reliably inhibitory and can thus be said to have been detected. Voluntary thresholds are given below the figure, and all dB values are re SPL. The saucer-shaped pattern described in the audiologist’s report is strikingly apparent in the configuration of eyeblink amplitudes noted in Fig. 1. Moreover, the reliability of this shape was supported by the presence of a
82
.25 I FREQUENCY
8 ( kHZ 1
Fig. 1. Mean reflex amplitude for a hearing-impaired child, L.S., as a function of the frequency and intensity of S1. Confidence intervals are presented with each point. Voluntary thresholds for L.S. were: 0.25 kHz = 40 dB, 1 kHz = 88 dB, 8 kHz = 20 dB, all re SPL.
strong quadratic orthogonal trend (F = 68.31, df = 1, 8, P < 0.001). The relatively greater inhibition produced at 8 kHz than at 1 kHz (and to a lesser extent 0.25 kHz) is also a reliable observation (supported by a linear trend across frequency, F = 7.35, df = 1, 8, P = 0.027), and accurately reflects the configuration of voluntary thresholds. Reflex modulation’s ability to follow the relative physical intensity of audible acoustical stimuli is apparent in the proper ordinal positions of the 90, 60 and 30 dB curves (for a linear trend for SPL, F = 15.31, df = 1,8, P = 0.004). Thus, as was true for hearingimpaired adults [ 31, the configurations present in the RM curves are reliable indicators of the relative extent and location of conventionally measured hearing losses. In examining the confidence intervals about each point, RMs sensitivity to stimuli at lo-15 dB SL becomes evident; however, the adverse effects of the high variability in behavior noted while testing L.S. also emerge. For example, there is a widening of the confidence intervals and a consequent decrease in the sensitivity of RM. Thus, while the 60 dB (SPL), 0.25 kHz pip was 20 dB above voluntary threshold, the extremely broad confidence interval surrounding that point overlapped the C level (indicated by an arrow at the ordinate), and thus prevented its reliable detection by RM. While the same discrepancy seems to be present at 30 dB for the 8 kHz stimulus, a more precise, correlated t-test between inhibited and corresponding C eyeblink amplitudes revealed inhibition by that acoustical stimulus to be reliable (t = 2.09, df = 8, P < 0.05, one-tailed). Except for the 0.25 kHz stimulus at 60 dB, RM was still sensitive to stimuli at about 10 dB above their voluntary threshold levels. CASE 2
K.Z. was an 11-year-old
boy with mild bilateral
sensorineural
hearing loss.
83
FREQUENCY
( kHZ )
Fig. 2. Mean reflex amplitude for a hearing-impaired child, K.Z., as a function of the frequency and intensity of S1. Confidence intervals are presented with each point. The uninhibited control level is indicated by an arrow at the ordinate. Voluntary thresholds for K.Z. were: 0.25 kHz = 49 dB, 1 kHz = 40 dB, 4 kHz = 55 dB, all re SPL.
His voluntary thresholds obtained about 5 min prior to the experiment for 0.25,1 and 4 kHz were 49,40 and 55 dB (SPL), respectively. For RM, 0.25, 1 and 4 kHz were presented to the right ear at 90,60 and 30 dB (SPL). Fig. 2 shows the results for K.Z. plotted again in “reversed” mm eyeblink amplitude. Voluntary thresholds (re SPL) are listed beneath the figure. The configuration of data points shown in Fig. 2 is characteristic of the generally shallow downward sloping pattern of K.Z.‘s voluntary audiogram. There was no main effect for frequency in the data. The tendency for RM to follow the relative intensities of the acoustical stimuli was supported statistically by a linear effect for SPL (F = 9.38, df = 1,8, P = 0.016). The greater spacing of inhibited blink amplitudes between 90 and 60 dB than between 60 and 30 dB (SPL), reflects the relative closeness of the three voluntary thresholds to 60 dB. This differential spacing is reliable and is described statistically by a quadratic trend for SPL (F = 6.35, df = 1, 8, P = 0.036). Thus, the RM pattern obtained during television viewing revealed the topographical characteristics of the underlying audiometric function. An individual points analysis done on the basis of the confidence intervals for K.Z. shows that RM was consistently sensitive to the presence of acoustical stimuli at 10 dB above voluntary threshold. All tones presented at 90 dB (SPL) were both audible on the voluntary measure and inhibitory on the reflex measure. At 60 dB the same is true for 0.25 kHz, which was only 11 dB above threshold, and for 1 kHz. Although 4 kHz was also audible it was but 5 dB above threshold at 60 dB, and was thus not reliably inhibitory. Finally, at 30 dB (SPL) the tones were neither audible nor inhibitory with respect to the reflex. CONCLUSIONS
Reflex modulation
was studied in two hearing-impaired children. Evi-
a4
dence of hearing of the test signals was provided by RM as low as lo-15 dB SL. In addition to this, the relative sensory impact or ‘loudness’ of each stimulus was represented objectively by the relative magnitude of reflex inhibition. This latter potentiality was shown by Reiter and Ison [6] to enable the charting of loudness growth and, in pathological cases, to permit diagnosis of loudness recruitment to be made. It is interesting that these results were obtained with RM even though subjects during testing were engaged in a distracting activity, e.g. watching television. The fact that so little in the way of voluntary cooperation or attention to the stimuli was required for proper evaluation by RM, encourages the prospects of its being used successfully as an audiometric test for the more ‘difficult-to-test’ child or adult. It is worth noting that reliable RM results have recently been observed in cases of functional hearing disorder [ 71 and in infants [ 21. Of further significance is that RM sensitivity was about equivalent (at lo-15 dB SL) for low, e.g. 0.25 kHz, as well as high frequency auditory stimulation, e.g. 4 kHz. Since the audiometric sensitivity of the other current objective techniques, e.g. brainstem audiometry and electrocochleography, drops off sharply below about 2 kHz [ 11, the good low frequency sensitivity of RM is a rather unique and important attribute. ACKNOWLEDGEMENTS
This research was done in partial fulfillment of the degree of Doctor of Philosophy awarded by the University of Rochester, and was supported by research grants from the National Institute of Neurological and Communication and Disorders and Stroke, NS 12443 and 1 F32 NS05918-01. The author would like to thank Drs. Cornelius P. Goetzinger and James R. Ison for their advise and encouragement. REFERENCES 1 Davis, J., Principles of electric response audiometry, Ann. Otol. (St. Louis) 28, Suppl. (1976) 85. 2 Marsh, R.R., Hoffman, H.S. and Stitt, C.L., Reflex inhibition audiometry: a new technique, Acta oto-laryng. (Stockh.), 85 (1978) 336-341. 3 Reiter, L.A., Development and Evaluation of Reflex Modulation as an Objective Audiometric Procedure. Doctoral Dissertation, University of Rochester, 1977, Dissert. Abstr., 24 (1978). 4 Reiter, L.A., Experiments re: the clinical application of reflex modulation audiometry, J. Speech Hear. Res., in press. 5 Reiter, L.A. and Ison, J.R., Inhibition of the human eyeblink reflex: evaluation of the sensitivity of the Wendt-Yerkes method for threshold detection, J. exp. Psychol., 3 (1977) 325-336. 6 Reiter, L.A. and Ison, J.R., Reflex modulation and loudness recruitment, J. audit. Res., in press. 7 Reiter, L.A., Goetzinger, C.P. and Press, S.R., Reflex modulation audiometry: a hearing test for the difficult-to-test, J. Speech Hear. Dis., in press.