CLINICAL ACOUSTIC REFLEX MEASUREMENTS IN I N F A N T S
THRESHOLD
Dennis A. Abahazi Fairview General Hospital, Cleveland, Ohio
Herbert J. Greenberg Bowling Green State University, Ohio
Acoustic reflex thresholds elicited using clinical acoustic impedance techniques were obtained on normal infants between one month and one year of age. Reflex activating signals of 500, 1000, 2000 Hz, low-pass, high-pass, and white noise were used. Less intensity was required to elicit the acoustic reflex to the noise than to the pure tones, with the 500-Hz tone requiring the greatest intensity. Inference of auditory thresholds from the acoustic reflex indicated the presence of normal hearing in the infant group.
T h e r e has been an increasing interest in using electroacoustic i m p e d a n c e meas u r e m e n t devices to assist in assessing the h e a r i n g sensitivity of y o u n g children. First, it has b e e n d e m o n s t r a t e d that acoustic i m p e d a n c e m e a s u r e m e n t s can provide v a l u a b l e i n f o r m a t i o n r e g a r d i n g the status of the m i d d l e ear. Second, i n d i r e c t m e a s u r e m e n t s of the reflex contractions of the m i d d l e ear muscles provide v a l u a b l e i n f o r m a t i o n r e g a r d i n g the sensitivity of the auditory m e c h a n i s m , since u n i q u e r e l a t i o n s h i p s have been f o u n d to exist between reflex thresholds of n o r m a l a n d sensorineural h e a r i n g - i m p a i r e d ears. O n l y a few investigations have been solely concerned with acoustic reflex thresh~:~ld m e a s u r e m e n t s of infants a n d children. Robertson, Peterson, a n d L a m b (1968) o b t a i n e d reflex thresholds to p u r e tones of 500, 1000, a n d 2000 Hz for c h i l d r e n from 18 to 36 months. T h e i r results i n d i c a t e d that as age increased, less intensity of the signal was r e q u i r e d to r the reflex. Jerger et al. (1974a) r e p o r t e d a n increase in the n u m b e r of reflexes at lower intensity levels as age increased from three m o n t h s to five years. I n addition, Jerger et al. (1974b) d e m o n s t r a t e d that a decrease in intensity was r e q u i r e d to elicit reflex t h r e s h o l d from b i r t h to five years. W h i l e most research on the acoustic reflex has been concerned w i t h the response to p u r e tones, investigations have shown that the reflex occurs at lower levels for bands of noise t h a n for pure tones (Moller, 1962; H u n g a n d 514
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ABAHAZI, GREENBERG"Threshold Measurements 515 Dallos, 1972). Data on normal-hearing adults collected by Deutsch (1972) demonstrated that the acoustic reflex was approximately 20 dB lower and occurred with more consistency at lower presentation levels when bands of noise were used instead of pure tones. Niemeyer and Sesterhenn (1974) described a test designed to distinguish normal hearing from a significant hearing loss by a comparison of reflex thresholds to pure tones and white noise. Jerger et al. (1974a) have also employed this technique in the testing of adults and children and demonstrated that the technique allows an approximate prediction of the magnitude of sensorineural hearing loss. T h e main purpose of this study was the collection of infant acoustic reflex threshold data to various stimuli in a clinical setting using clinical equipment. A secondary goal was to investigate the relationship between age and the intensity of the acoustic signal required to elicit the reflex. METHOD
Subjects Impedance measurements were obtained on male and female infants from one month to one year of age. Infants were tested at a pediatrician's office as part of a routine physical examination and were judged by the pediatrician to have otoscopically normal ears. Included were those infants who had been fullterm babies with normal deliveries according to the pediatrician's records. A total of 108 infants were seen for impedance measurements. Tympanometry was used to evaluate the condition of the middle ear by obtaining a sweep tympanogram from +200 to --200 mm H20 pressure. Those infants whose tympanograms had pressure peaks beyond ___50 m m H20 were rejected. Of the original group, 46 infants were eliminated either because of failure to meet the above criteria, or excessive movement during testing. Acoustic reflexes to all of the stimuli were obtained on 23 infants. Results for less than the total number of stimuli were obtained on the remaining 39 infants.
Instrumentation An American Electromedics Impedance Audiometer (Model 83) was used to perform the impedance measurements. T h e unit was coupled to the ear canal with a conventional insert tip to deliver the reflex monitoring signal of 220 Hz. T o present the reflex activating signal, a Telephonics TDH-39 earphone in an M X - - 4 1 ] A R cushion was placed over the infant's ear and held tightly in place by the mother's hand so that the earphone was over the ear canal.
Signal Presentation T h e reflex activating signals were 500, 1000, and 2000 Hz pure tones, and white noise, low-pass, and high-pass noise. T h e upper and lower cutoff fre-
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516 JOURNALOF SPEECH AND HEARING DISORDERS
XLII 514-519 1977
quency for the low- and high-pass noise was 2600 Hz as is incorporated in the impedance audiometer. T h e intensity of the reflex activating signals was calibrated daily using a General R a d i o (Model 1565-A) sound level meter and T y p e 1 coupler (Model 1560-P82). T h e selection of the ear for the reflex activating signal was alternated from infant to infant. Acoustic presentations of approximately one-sec duration began at approximately 70-dB SPL and ascended in 5-dB steps until the reflex threshold was obtained for two of three presentations. T h e ascending method was used to reduce the possibility of startle responses. Acoustic reflex thresholds were determined by a deflection of at least one unit on the impedance device's compliance change meter set at the R sensitivity setting in response to signal presentation.
Inference of Auditory Thresholds from the Acoustic Reflex Sensorineural hearing loss can be identified by a decrease in the difference between acoustic reflex thresholds to noise and pure tones (Niemeyer and Sesterhenn, 1974; Jerger et al., 1974a). In this study, two techniques were employed to calculate this difference in an a t t e m p t to support the pediatrician's diagnosis of normal hearing. T h e first procedure used was that specified by the manufacturer of the impedance measuring device (American Electromedics Corp., 1974) and included obtaining the mean of the acoustic reflex thresholds (in SPL) for 500, 1000, and 2000 Hz. T h e acoustic reflex threshold for white noise was then subtracted from this value. This score was obtained for the 23 infants from whom reflexes were obtained to these stimuli and compared to a difference score obtained on 10 normal-hearing college students. A n o t h e r difference score was determined using the Jerger et al. (1974a) method. RESULTS
Stimulus Differences in Acoustic Reflex Thresholds Pure-tone acoustic reflex thresholds were converted to sound pressure levels. T h e intensities required to elicit the acoustic reflex were pooled together across age levels for each acoustic stimulus. Duncan's multiple range test (Edwards, 1972) was used to determine the presence of significant differences between the various acoustic stimuli. Mean acoustic reflex thresholds averaged across age for the various stimuli are shown in T a b l e 1. Included also are the ranges and the n u m b e r of infants on which the averages are based. As can be noted, less intensity was required to elicit the acoustic reflex to the noise signals. Significant differences (p < 0.01) were present between the reflex thresholds to the 500 Hz stimulus and all the other acoustic stimuli. No significant differences existed between the thresholds to the 1000 and 2000 Hz stimuli, but the thresholds to these two stimuli differed significantly (p < 0.01) from all the other signals. T h e reflex
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A B A H A Z I , GREENBERG: Threshold Measurements
517
TABLE 1, Mean i n f a n t acoustic reflex thresholds in dB SPL averaged across age for pure tone and noise stimuli. Ranges and samples sizes are also included. Any two t r e a t m e n t means n o t underscored by the same line are significantly different at the 0.01 level. Any two t r e a t m e n t means underscored by the same line are not significantly different. iii i
i
i
i
i
i iii i ii
B 1000 Hz
C 2000 Hz
D Low-Pass Noise
E High-Pass Noise
F White Noise
105.3 91.5-116.5 54
97.9 87-112 51
98.9 84-114 47
90.7 70-105 48
88.3 75-105 51
84.2 65-100 64
Parameter dB SPL Range N
i
A 500 Hz
thresholds to the low-pass and high-pass stimuli did not differ significantly from each other, but differed significantly (p ~ 0.01) from the other acoustic stimuli. T h e analysis of the acoustic reflex data for white noise indicated that these thresholds differed significantly (p < 0.01) from all the other stimuli.
Age Differences in Acoustic Reflex Thresholds Figure 1 presents the results of the effects of age on the acoustic reflex
t2C | SO0 Hz 9 1000 Hz 9 2000 Hz
.I
s_ ~1(l m m
~
"3 109
80 t)
0
70-
1
I
,
....i
,
I
,
,
,
1-2
2-3
3-4
4-S
5-6
6-7
7-8
8-9
i 9-10
10-11
11-12
Age (Months)
Figure 1. Mean infant acoustic reflex thresholds as a function of age for pure tones and white noise.
threshold. Mean thresholds are shown for pure tones and white noise as a function of maturation. T h e sample size varied from one subject at nine to 10 months to 11 subjects at three to four months. These data suggest a possible age trend in the acoustic reflex threshold with slightly less signal intensity required at 12 months.
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518
JOURNAL OF SPEECH AND HEARING DISORDERS
Prediction
XLll
514-519 1977
of Auditory Thresholds from the Acoustic Reflex
T h e complete data obtained on 23 infants, that is, the acoustic reflex thresholds for all of the pure tones and for the white-noise stimulus, were analyzed to determine if the difference between the pure-tone and white-noise acoustic reflex thresholds were indicative of normal hearing sensitivity. T h e acoustic reflex threshold difference for pure tones and white noise was 21 dB for the infants, compared to 17 dB for the adult comparison group. Both methods of calculation, the equipment manufacturer's technique, and the technique reported by Jerger et al. (1974a) produced identical results, thus reinforcing probability of the absence of any sensorineural pathology in the infant group.
DISCUSSION As has been previously demonstrated, this investigation determined that lesser signal intensity was required to elicit the infant's acoustic reflex to noise signals than to pure tones. T h e data obtained in this study are approximately 5 dB higher for pure tones and about 10 dB higher for white noise as compared to the most recent study of the infant's acoustic reflex threshold (Margolis and Popelka, 1975). These differences can be attributed to the clinical measurement system used in this study and the criterion adopted for reflex response identification. This study suggested that as age increased, less intensity of the signal was required to elicit the acoustic reflex. Previous research has suggested a relationship between the age of the subject and the intensity of the acoustic signal required to elicit the reflex. However, the differences between age groups found in the present study were slight and might be due to variations in sample size and variability in the behavior of the infants as well as to neurological maturation. This investigation also demonstrated that the inference of auditory thresholds from the acoustic reflex is possible in norlnal-hearing infants. It is obvious that, especially in infants, errors in inferring hearing loss are likely to occur. Some investigators may suggest the prediction of the severity and slope of a hearing loss from the reflexes. While these calculations have been shown to be valuable with adult subjects with sensorineural pathologies, it would be nmre prudent to use a comparison of reflexes to pure tones and noise to determine the presence or absence of normal hearing. This is desirable until such time that longitudinal data have confirmed or denounced the predictive accuracy of this technique on infants. T h e difficulties in obtaining impedance measurements on this population are obvious. The resistance to any foreign object in the ear canal reduced the sample size considerably, and no doubt this has accounted for the paucity of large scale investigations on this age group. T h e very young infants (one to three months) offered little resistance to testing, and some of the infants near
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ABAHAZI, GREENBERG: Threshold Measurements 519
o n e y e a r of age e x h i b i t e d q u i e t b e h a v i o r . I m p e d a n c e m e a s u r e m e n t s s h o u l d c e r t a i n l y be a t t e m p t e d for i n f a n t s in t h e age r a n g e s s t u d i e d . H o w e v e r , i n t h e p r e s e n t s t u d y , a c o u s t i c reflexes to t h e t h r e e p u r e tones a n d t h r e e noises c o u l d be o b t a i n e d o n o n l y 2 1 % of t h e c h i l d r e n . T h e use o[ several test sessions s h o u l d be c o n s i d e r e d b e [ o r e a n a c c u r a t e p r e d i c t i v e a s s e s s m e n t of h e a r i n g c a n be m a d e . I n a d d i t i o n , t h e use of s t r i p c h a r t r e c o r d i n g s of t h e a c o u s t i c reflex s h o u l d be c o n s i d e r e d to i n c r e a s e the a c c u r a c y of t h e r e s p o n s e m e a s u r e m e n t .
ACKNOWLEDGMENT This article is based in part on a doctoral dissertation completed at Bowling Green State University (1975) under the supervision of the second author. Send requests for reprints to 9 Herbert J. Greenberg, Communication Sciences Laboratory, Bowling Green State University, Bowling Green, Ohio 43403. REFERENCES
DEu'rscH, L., The threshold of the stapedius reflex for pure tones and noise stimuli. Acta Oto-lar., 74, 248-251 (1972). EowAlu)s, A., Experimental Design in Psychological Research. New York: Holt, Rinehart and Winston (1972). HUNG, I., and DALLOS, P., Study of the acoustic reflex in human beings. I. Dynamic characteristics. J. acoust. Soc. Am., 52, 1168-1180 (1972). JEk(;ER, J., BURNEY, P., MAULmN, L., and CRUMe, B., Predicting hearing loss from the acoustic reflex. J. Speech Hearing Dis., 39, 11-22 (1974a). Jr:RGra, S., Jr:RcrR, J., MAULOIN, L., and SVCAL, P., Studies in impedance audiometry. II. Children less than 6 years ohl. Archs Otolar., 99, 1-9 (1974b). Manual ]or Impedance Audiometer, Model 83. Dobbs Ferry, N.Y.: American Electromedics Corporation (1974). MAR(;OHS, R. H., and POI'ELKA, G. R., Static and dynamic acoustic impedance measurements in infant ears. J. Speech Hearing Res., 18, 435--443 (1975). MOLLEg, A. R., Acoustic reflex in man. J. acoust. Soc. Am., 15, 1524-1534 (1962). NIEMEYER, W., and SESTERHENN,G., Calculating the hearing threshold from the stapedius reflex threshold for different sound stimuli. Audiology, 13, 421-427 (1974). ROBEkTSON, E., Pr:rE~tSON, j., and LAMB, L., Relative impedance measurements in young children. Archs Otolar., 88, 162-I68 (1968). Received May 18, 1976. Accepted April 18, 1977.
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THRESHOLD
Dennis A. Abahazi Fairview General Hospital, Cleveland, Ohio
Herbert J. Greenberg Bowling Green State University, Ohio
Acoustic reflex thresholds elicited using clinical acoustic impedance techniques were obtained on normal infants between one month and one year of age. Reflex activating signals of 500, 1000, 2000 Hz, low-pass, high-pass, and white noise were used. Less intensity was required to elicit the acoustic reflex to the noise than to the pure tones, with the 500-Hz tone requiring the greatest intensity. Inference of auditory thresholds from the acoustic reflex indicated the presence of normal hearing in the infant group.
T h e r e has been an increasing interest in using electroacoustic i m p e d a n c e meas u r e m e n t devices to assist in assessing the h e a r i n g sensitivity of y o u n g children. First, it has b e e n d e m o n s t r a t e d that acoustic i m p e d a n c e m e a s u r e m e n t s can provide v a l u a b l e i n f o r m a t i o n r e g a r d i n g the status of the m i d d l e ear. Second, i n d i r e c t m e a s u r e m e n t s of the reflex contractions of the m i d d l e ear muscles provide v a l u a b l e i n f o r m a t i o n r e g a r d i n g the sensitivity of the auditory m e c h a n i s m , since u n i q u e r e l a t i o n s h i p s have been f o u n d to exist between reflex thresholds of n o r m a l a n d sensorineural h e a r i n g - i m p a i r e d ears. O n l y a few investigations have been solely concerned with acoustic reflex thresh~:~ld m e a s u r e m e n t s of infants a n d children. Robertson, Peterson, a n d L a m b (1968) o b t a i n e d reflex thresholds to p u r e tones of 500, 1000, a n d 2000 Hz for c h i l d r e n from 18 to 36 months. T h e i r results i n d i c a t e d that as age increased, less intensity of the signal was r e q u i r e d to r the reflex. Jerger et al. (1974a) r e p o r t e d a n increase in the n u m b e r of reflexes at lower intensity levels as age increased from three m o n t h s to five years. I n addition, Jerger et al. (1974b) d e m o n s t r a t e d that a decrease in intensity was r e q u i r e d to elicit reflex t h r e s h o l d from b i r t h to five years. W h i l e most research on the acoustic reflex has been concerned w i t h the response to p u r e tones, investigations have shown that the reflex occurs at lower levels for bands of noise t h a n for pure tones (Moller, 1962; H u n g a n d 514
Downloaded From: https://jshd.pubs.asha.org/ by a Univ of Auckland User on 03/31/2018 Terms of Use: https://pubs.asha.org/ss/rights_and_permissions.aspx
ABAHAZI, GREENBERG"Threshold Measurements 515 Dallos, 1972). Data on normal-hearing adults collected by Deutsch (1972) demonstrated that the acoustic reflex was approximately 20 dB lower and occurred with more consistency at lower presentation levels when bands of noise were used instead of pure tones. Niemeyer and Sesterhenn (1974) described a test designed to distinguish normal hearing from a significant hearing loss by a comparison of reflex thresholds to pure tones and white noise. Jerger et al. (1974a) have also employed this technique in the testing of adults and children and demonstrated that the technique allows an approximate prediction of the magnitude of sensorineural hearing loss. T h e main purpose of this study was the collection of infant acoustic reflex threshold data to various stimuli in a clinical setting using clinical equipment. A secondary goal was to investigate the relationship between age and the intensity of the acoustic signal required to elicit the reflex. METHOD
Subjects Impedance measurements were obtained on male and female infants from one month to one year of age. Infants were tested at a pediatrician's office as part of a routine physical examination and were judged by the pediatrician to have otoscopically normal ears. Included were those infants who had been fullterm babies with normal deliveries according to the pediatrician's records. A total of 108 infants were seen for impedance measurements. Tympanometry was used to evaluate the condition of the middle ear by obtaining a sweep tympanogram from +200 to --200 mm H20 pressure. Those infants whose tympanograms had pressure peaks beyond ___50 m m H20 were rejected. Of the original group, 46 infants were eliminated either because of failure to meet the above criteria, or excessive movement during testing. Acoustic reflexes to all of the stimuli were obtained on 23 infants. Results for less than the total number of stimuli were obtained on the remaining 39 infants.
Instrumentation An American Electromedics Impedance Audiometer (Model 83) was used to perform the impedance measurements. T h e unit was coupled to the ear canal with a conventional insert tip to deliver the reflex monitoring signal of 220 Hz. T o present the reflex activating signal, a Telephonics TDH-39 earphone in an M X - - 4 1 ] A R cushion was placed over the infant's ear and held tightly in place by the mother's hand so that the earphone was over the ear canal.
Signal Presentation T h e reflex activating signals were 500, 1000, and 2000 Hz pure tones, and white noise, low-pass, and high-pass noise. T h e upper and lower cutoff fre-
Downloaded From: https://jshd.pubs.asha.org/ by a Univ of Auckland User on 03/31/2018 Terms of Use: https://pubs.asha.org/ss/rights_and_permissions.aspx
516 JOURNALOF SPEECH AND HEARING DISORDERS
XLII 514-519 1977
quency for the low- and high-pass noise was 2600 Hz as is incorporated in the impedance audiometer. T h e intensity of the reflex activating signals was calibrated daily using a General R a d i o (Model 1565-A) sound level meter and T y p e 1 coupler (Model 1560-P82). T h e selection of the ear for the reflex activating signal was alternated from infant to infant. Acoustic presentations of approximately one-sec duration began at approximately 70-dB SPL and ascended in 5-dB steps until the reflex threshold was obtained for two of three presentations. T h e ascending method was used to reduce the possibility of startle responses. Acoustic reflex thresholds were determined by a deflection of at least one unit on the impedance device's compliance change meter set at the R sensitivity setting in response to signal presentation.
Inference of Auditory Thresholds from the Acoustic Reflex Sensorineural hearing loss can be identified by a decrease in the difference between acoustic reflex thresholds to noise and pure tones (Niemeyer and Sesterhenn, 1974; Jerger et al., 1974a). In this study, two techniques were employed to calculate this difference in an a t t e m p t to support the pediatrician's diagnosis of normal hearing. T h e first procedure used was that specified by the manufacturer of the impedance measuring device (American Electromedics Corp., 1974) and included obtaining the mean of the acoustic reflex thresholds (in SPL) for 500, 1000, and 2000 Hz. T h e acoustic reflex threshold for white noise was then subtracted from this value. This score was obtained for the 23 infants from whom reflexes were obtained to these stimuli and compared to a difference score obtained on 10 normal-hearing college students. A n o t h e r difference score was determined using the Jerger et al. (1974a) method. RESULTS
Stimulus Differences in Acoustic Reflex Thresholds Pure-tone acoustic reflex thresholds were converted to sound pressure levels. T h e intensities required to elicit the acoustic reflex were pooled together across age levels for each acoustic stimulus. Duncan's multiple range test (Edwards, 1972) was used to determine the presence of significant differences between the various acoustic stimuli. Mean acoustic reflex thresholds averaged across age for the various stimuli are shown in T a b l e 1. Included also are the ranges and the n u m b e r of infants on which the averages are based. As can be noted, less intensity was required to elicit the acoustic reflex to the noise signals. Significant differences (p < 0.01) were present between the reflex thresholds to the 500 Hz stimulus and all the other acoustic stimuli. No significant differences existed between the thresholds to the 1000 and 2000 Hz stimuli, but the thresholds to these two stimuli differed significantly (p < 0.01) from all the other signals. T h e reflex
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A B A H A Z I , GREENBERG: Threshold Measurements
517
TABLE 1, Mean i n f a n t acoustic reflex thresholds in dB SPL averaged across age for pure tone and noise stimuli. Ranges and samples sizes are also included. Any two t r e a t m e n t means n o t underscored by the same line are significantly different at the 0.01 level. Any two t r e a t m e n t means underscored by the same line are not significantly different. iii i
i
i
i
i
i iii i ii
B 1000 Hz
C 2000 Hz
D Low-Pass Noise
E High-Pass Noise
F White Noise
105.3 91.5-116.5 54
97.9 87-112 51
98.9 84-114 47
90.7 70-105 48
88.3 75-105 51
84.2 65-100 64
Parameter dB SPL Range N
i
A 500 Hz
thresholds to the low-pass and high-pass stimuli did not differ significantly from each other, but differed significantly (p ~ 0.01) from the other acoustic stimuli. T h e analysis of the acoustic reflex data for white noise indicated that these thresholds differed significantly (p < 0.01) from all the other stimuli.
Age Differences in Acoustic Reflex Thresholds Figure 1 presents the results of the effects of age on the acoustic reflex
t2C | SO0 Hz 9 1000 Hz 9 2000 Hz
.I
s_ ~1(l m m
~
"3 109
80 t)
0
70-
1
I
,
....i
,
I
,
,
,
1-2
2-3
3-4
4-S
5-6
6-7
7-8
8-9
i 9-10
10-11
11-12
Age (Months)
Figure 1. Mean infant acoustic reflex thresholds as a function of age for pure tones and white noise.
threshold. Mean thresholds are shown for pure tones and white noise as a function of maturation. T h e sample size varied from one subject at nine to 10 months to 11 subjects at three to four months. These data suggest a possible age trend in the acoustic reflex threshold with slightly less signal intensity required at 12 months.
Downloaded From: https://jshd.pubs.asha.org/ by a Univ of Auckland User on 03/31/2018 Terms of Use: https://pubs.asha.org/ss/rights_and_permissions.aspx
518
JOURNAL OF SPEECH AND HEARING DISORDERS
Prediction
XLll
514-519 1977
of Auditory Thresholds from the Acoustic Reflex
T h e complete data obtained on 23 infants, that is, the acoustic reflex thresholds for all of the pure tones and for the white-noise stimulus, were analyzed to determine if the difference between the pure-tone and white-noise acoustic reflex thresholds were indicative of normal hearing sensitivity. T h e acoustic reflex threshold difference for pure tones and white noise was 21 dB for the infants, compared to 17 dB for the adult comparison group. Both methods of calculation, the equipment manufacturer's technique, and the technique reported by Jerger et al. (1974a) produced identical results, thus reinforcing probability of the absence of any sensorineural pathology in the infant group.
DISCUSSION As has been previously demonstrated, this investigation determined that lesser signal intensity was required to elicit the infant's acoustic reflex to noise signals than to pure tones. T h e data obtained in this study are approximately 5 dB higher for pure tones and about 10 dB higher for white noise as compared to the most recent study of the infant's acoustic reflex threshold (Margolis and Popelka, 1975). These differences can be attributed to the clinical measurement system used in this study and the criterion adopted for reflex response identification. This study suggested that as age increased, less intensity of the signal was required to elicit the acoustic reflex. Previous research has suggested a relationship between the age of the subject and the intensity of the acoustic signal required to elicit the reflex. However, the differences between age groups found in the present study were slight and might be due to variations in sample size and variability in the behavior of the infants as well as to neurological maturation. This investigation also demonstrated that the inference of auditory thresholds from the acoustic reflex is possible in norlnal-hearing infants. It is obvious that, especially in infants, errors in inferring hearing loss are likely to occur. Some investigators may suggest the prediction of the severity and slope of a hearing loss from the reflexes. While these calculations have been shown to be valuable with adult subjects with sensorineural pathologies, it would be nmre prudent to use a comparison of reflexes to pure tones and noise to determine the presence or absence of normal hearing. This is desirable until such time that longitudinal data have confirmed or denounced the predictive accuracy of this technique on infants. T h e difficulties in obtaining impedance measurements on this population are obvious. The resistance to any foreign object in the ear canal reduced the sample size considerably, and no doubt this has accounted for the paucity of large scale investigations on this age group. T h e very young infants (one to three months) offered little resistance to testing, and some of the infants near
Downloaded From: https://jshd.pubs.asha.org/ by a Univ of Auckland User on 03/31/2018 Terms of Use: https://pubs.asha.org/ss/rights_and_permissions.aspx
ABAHAZI, GREENBERG: Threshold Measurements 519
o n e y e a r of age e x h i b i t e d q u i e t b e h a v i o r . I m p e d a n c e m e a s u r e m e n t s s h o u l d c e r t a i n l y be a t t e m p t e d for i n f a n t s in t h e age r a n g e s s t u d i e d . H o w e v e r , i n t h e p r e s e n t s t u d y , a c o u s t i c reflexes to t h e t h r e e p u r e tones a n d t h r e e noises c o u l d be o b t a i n e d o n o n l y 2 1 % of t h e c h i l d r e n . T h e use o[ several test sessions s h o u l d be c o n s i d e r e d b e [ o r e a n a c c u r a t e p r e d i c t i v e a s s e s s m e n t of h e a r i n g c a n be m a d e . I n a d d i t i o n , t h e use of s t r i p c h a r t r e c o r d i n g s of t h e a c o u s t i c reflex s h o u l d be c o n s i d e r e d to i n c r e a s e the a c c u r a c y of t h e r e s p o n s e m e a s u r e m e n t .
ACKNOWLEDGMENT This article is based in part on a doctoral dissertation completed at Bowling Green State University (1975) under the supervision of the second author. Send requests for reprints to 9 Herbert J. Greenberg, Communication Sciences Laboratory, Bowling Green State University, Bowling Green, Ohio 43403. REFERENCES
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