Effect of age on prediction of sensorineural hearing level from the acoustic reflex

To study the effect of age on prediction of hearing level from the acoustic reflex, we compared reflex prediction with the actual hearing level in 505 patients. The following three age groups were defined: 130 children aged 2 to 12 years; 158 young adults aged 20 to 40 years; and 217 old adults aged 60 to 90 years. Prediction was substantially more accurate in the children's group than in either adult group.     

Neonatal acoustic reflex —Relationship to birth weight, postnatal age

Ipsilateral acoustic reflex was tested in 75 normal neonates using a 220 H2 probe tone. The age of the neonates ranged from 24 hours to 192 hours and the birth weight from 2.5 kg to 3.8 kg. It was observed that the reflex is detectable in all neonates more than 4 days old and has a significant relationship with the birth weight. We feel that this test should be utilized routinely as one of the investigative procedures in all neonatal auditory screening programmes.     

The effects of childhood otitis media on the acoustic reflex threshold at age 15

Previous research has found that childhood otitis media leads to elevated adulthood acoustic reflex thresholds because of worsened audiometric thresholds in the stimulation ear, and abnormality of the tympanic membrane in the ear from which acoustic reflexes were measured. To confirm and expand this finding, our research utilized longitudinal data from 631 general-population-sampled children assessed between ages 5 and 15. Otitis media was assessed to age 9, audiometric thresholds were measured at age 11, and otoscopy and acoustic reflex thresholds testing were performed at age 15. Our findings support the earlier research, in that acoustic reflex threshold was higher in those with the worst experience of childhood otitis media. However, this was directly mediated not by audiometric threshold in the ear to which the stimulus was delivered, but by the amount of tympanic membrane abnormality in both the stimulus and probe ears. This appeared to have an effect independent of audiometric threshold. Furthermore, only those who suffered the worst, persistent, binaural childhood otitis media showed raised acoustic reflex thresholds.     

The effects of childhood otitis media on the acoustic reflex threshold at age 15

Previous research has found that childhood otitis media leads to elevated adulthood acoustic reflex thresholds because of worsened audiometric thresholds in the stimulation ear, and abnormality of the tympanic membrane in the ear from which acoustic reflexes were measured. To confirm and expand this finding, our research utilized longitudinal data from 631 general-population-sampled children assessed between ages 5 and 15. Otitis media was assessed to age 9, audiometric thresholds were measured at age 11, and otoscopy and acoustic reflex thresholds testing were performed at age 15. Our findings support the earlier research, in that acoustic reflex threshold was higher in those with the worst experience of childhood otitis media. However, this was directly mediated not by audiometric threshold in the ear to which the stimulus was delivered, but by the amount of tympanic membrane abnormality in both the stimulus and probe ears. This appeared to have an effect independent of audiometric threshold. Furthermore, only those who suffered the worst, persistent, binaural childhood otitis media showed raised acoustic reflex thresholds.     

Acoustic reflex amplitude and noise-induced hearing loss

Acoustic reflex maximum amplitude measurements elicited both contralaterally and ipsilaterally were obtained from subjects with noise-induced hearing loss and compared with those obtained from normal-hearing subjects. The eliciting signal was a pure tone of 1 kHz presented for 1,000 ms. The groups were matched on age, sex, static immittance and ear canal volume. Acoustic reflex amplitudes were clearly reduced in noise-impaired subjects compared with normal-hearing subjects at a frequency where their hearing thresholds were normal.     

Adaptation of the acoustic reflex

Acoustic reflex adaptation is reviewed in normal and abnormal auditory systems. The measurement variables affecting the acoustic reflex threshold are discussed with reference to the intensity level above reflex threshold at which the adaptation is measured. The effects of the activator frequency and activator intensity level on the time course of normal reflex adaptation are reviewed. The diagnostic application of acoustic reflex adaptation is discussed with reference to the different definitions of abnormality found in the literature. The acoustic reflex patterns, including absence, threshold, and adaptation of the reflex, are reported in patients with different degrees of hearing loss, in order to identify the false-positive rates associated with cochlear hearing losses. Finally, the diagnostic accuracy of acoustic reflexes is discussed in subjects having lesions of the CNVIII, brain stem, CNVII, and neuromuscular systems. In summary, a method is advocated for measuring acoustic reflex adaptation over 10 seconds, which allows analysis at both 5 and 10 seconds. Further research is needed on procedural variables including activator intensity level and ipsilateral recording methods, which may increase the diagnostic accuracy of acoustic reflex adaptation.     

The acoustic reflex and loudness recruitment

Loudness balance and acoustic reflex tests were conducted on 11 hearing impaired patients. At all frequencies tested, equal loudness judgments made by each patient occurred at acoustic reflex threshold levels in each ear. Test results were classified into three general patterns and a Difference Ratio Quotient (DRQ) expressed the relationship between binaural acoustic reflex and pure tone thresholds. Additional information was derived from the DRQ formula to permit more accurate quantification of recruitment.     

Influence of the acoustic reflex on vowel recognition

Computer synthesized vowels of 50- and 300-ms duration were presented to normal-hearing listeners at a moderate and high sound pressure level (SPL). Presentation at the high SPL resulted in poor recognition accuracy for vowels of a duration (50 ms) shorter than the latency of the acoustic stapedial reflex. Presentation level had no effect on recognition accuracy for vowels of sufficient duration (300 ms) to elicit the reflex. The poor recognition accuracy for the brief, high intensity vowels was significantly improved when the reflex was preactivated. These results demonstrate the importance of the acoustic reflex in extending the dynamic range of the auditory system for speech recognition.     

Early development of the acoustic reflex

Acoustic reflex testing was conducted on 2-day-old and on 6-week-old infants to determine how frequently, if at all, the acoustic reflex occurs, if it can be reliably observed, and also to determine what is the mean normal acoustic reflex threshold for pure tones and broad-band noise in these populations. Twenty normal infants were tested in each group. Each infant was considered to be normal by the following criteria: full term, normal pregnancy normal pregnancy and delivery, birth weight greater than 2500 g, 5-min Apgar of 7 or greater, and considered to be not at risk for hearing loss by the absence of any high risk factors. Subjects were tested following feedings. Acoustic reflexes were obtained from subjects with normal tympanograms (+/- 50 mm H2O) for 500, 1,000, 2,000, and 4,000 Hz and broad-band noise stimuli. Behavioral responses were common, requiring quieting pauses in testing and repeated stimulation for habituation of the behavioral component. Acoustic reflexes were observed, and normative reflex threshold data were obtained. The number of reflexes obtained and the mean acoustic reflex thresholds for these age-groups are reported.     

Temporal summation of the acoustic reflex

A signal-averaging technique was used to minimize acoustic reflex measurement system noise while preserving temporal fidelity. In normal listeners, the interaction of signal intensity and signal duration was explored at visual detection threshold (VDT) and at varying suprathreshold signal levels. Reflex amplitude increases, with signal intensity, at a rate which changes as a function of signal duration, a finding which complicates the interpretation of temporal summation data based on VDT. A theoretical model is proposed to explain the complex interactions of signal intensity, duration, and band width on the amplitude of the acoustic reflex.     

The sensitization of acoustic stapedius reflex

The acoustic stapedius reflex, which normally occurs at a hearing level of about 85 dB, can be detected at lower levels by means of sensitization. The technique is to apply reflex-eliciting tone and the facilitating tone stimulation. The high-frequency acoustic stapedius reflex can then be detected in this procedure under low-frequency facilitating. When hearing is normal, significant difference can be demonstrated between conventional and facilitated reflex threshold. There is a great amount of reflex threshold improvement with sensitization. Sensorineural hearing loss allowed small or no reflex threshold change with sensitization.     

Temporal characteristics of the acoustic reflex

Temporal aspects of the acoustic reflex response were estimated for normally hearing subjects, subjects with noise-induced hearing loss and children with sensorineural hearing impairment. Onset latency and rise/fall times of admittance change were measured from the averaged responses (8 presentations) to tone bursts of 250 ms durations and 10 ms rise/fall time. Tone burst frequency was varied from 500 to 4 000 Hz. No differences between groups were observed for onset responses. Compared to the data from normally hearing subjects, the offset responses were slightly longer for subjects with noise-induced hearing loss and were considerably longer for hearing-impaired children. Due to the prolongation seen for noise-exposed subjects, it is difficult to interpret these data in terms of site of lesion. Still, the differences between hearing-impaired children and normal subjects suggest that acoustic reflex offset latency may be a useful screening device.     

Influence of stimulus duration and intensity on acoustic reflex parameters

Four acoustic reflex parameters (latency, duration, amplitude, recruitment time) in response to stimuli lasting 1 000 to 50 msec with an initial intensity of 95 dB SPL p.e. were studied in four sets of experiments. In each set of experiments, each halving of the stimulus duration was accompanied by a 3, 4, 5 and 6 dB SPL p.e. increase respectively (exchange rates: 3, 4, 5 and 6 dB SPL p.e.). It was found that latency was dependent on the threshold only and unaffected by either duration and intensity. Amplitude and recruitment time were mainly determined by energy content of the stimulus, whereas duration of contraction was solely dependent on the stimulus duration. These experiments also demonstrate that, with reference to stimuli employed, an increase of 3 dB SPL p.e. each halving of the stimulus duration is unable to maintain unchanged the environmental acoustic energy reaching the inner ear.     

Auditory brain-stem response and acoustic reflex test

Auditory brain-stem response (ABR) and acoustic reflex test (ART) results were reviewed for 30 patients with cerebellopontile angle tumors and for 30 patients without tumor. Patients included in the nontumor group were selected to match the audiometric configurations for individual patients in the tumor group. The ABR waveforms were abnormal for all but one of the patients with tumor and for seven of the patients without tumor. The ART results were abnormal for 25 of the patients with tumor and two of the patients without tumor. Patients without tumor yielding abnormal ABR results usually had more severe hearing losses than the patients without tumor who demonstrated normal ABR waveforms. The ABR and ART merit continued use in the audiologic examination of patients suspected of having retrocochlear lesions, but obviously, degree of hearing loss and other medical information must be considered also when retrocochlear lesions are suspected.     

Safety and clinical performance of acoustic reflex tests

OBJECTIVE: Safety and effectiveness of acoustic reflex tests are important issues because these tests are widely applied to screen for retrocochlear pathology. Previous studies have reported moderately high sensitivity and specificity for detection of acoustic neuroma. However, there have been reports of possible iatrogenic hearing loss resulting from acoustic reflex threshold (ART) and decay (ARD) tests. This study assessed safety and clinical performance of ART tests for detection of acoustic neuroma. DESIGN: We report a case in which ARD testing resulted in a significant bilateral permanent threshold shift. This case was the impetus for us to investigate the clinical utility of ART and ARD tests. We analyzed sensitivity and specificity of ART, as well as asymmetry in pure-tone thresholds (PTT) for detection of acoustic neuroma in 56 tumor and 108 non-tumor ears. RESULTS AND CONCLUSIONS: Sensitivity and specificity were higher for PTT asymmetry than for ART. Ipsilateral ART at 1000 Hz had poor sensitivity and specificity for detection of acoustic neuroma, and involves some potential risk to residual hearing for presentation levels higher than 115 dB SPL. Approximately half of the acoustic neuroma group had ipsilateral ARTs that would require administration of ARD tests at levels exceeding 115 dB SPL. Therefore, we conclude that PTT asymmetry is a more effective test for detection of acoustic neuroma, and involves no risk to residual hearing. Future studies of contralateral reflex threshold and ARD in combination with PTT asymmetry are recommended.     

The importance of acoustic reflex for communication

Purpose

The purpose of the study was to compare the speech recognition capacity between listeners with and without acoustic reflex using different types of noises and intensities.

Materials and methods

We studied 18 women allocated to 2 groups: acoustic reflex present (20 ears) and absent (16 ears). They were presented with 180 disyllable words (90 to each ear), emitted randomly at a fixed intensity of 40 dB above the pure tone average hearing level. At the same time, 3 types of noises were presented ipsilaterally (white, pink, and speech), one at a time, at 3 intensities: 40, 50, and 60 dB above the pure tone average hearing level.

Results

The ages and auditory thresholds were statistically equal between the groups. There was a significant difference in mean number of hits between the 2 groups for the 3 types of noises used. There was also a significant difference in mean number of hits for noise type and intensity when white and pink noise was used at 40 and 50 dB and for all the intensities when speech was used.

Conclusion

Acoustic reflex helps communication in high-noise environments and is more efficient for speech sounds.     

The time course of the acoustic reflex

The time course of the impedance changes caused by the contralateral acoustic reflex was investigated in five normal hearing, young adult subjects The acoustic reflex function was measured with equipment having a time constant of 15 milliseconds which permitted precise temporal measures. Temporal intervals from signal onset and termination to various portions of the acoustic reflex function were derived using an analysis procedure based on the slope function underlying the acoustic reflex response. These temporal intervals are related to physiological events underlying the acoustic reflex.     

Normative characteristics of ipsilateral acoustic reflex adaptation

Contralateral and ipsilateral acoustic reflex adaptation (decay) were examined using 500-, 1000-, and 2000-Hz tonal activators for stimulation periods of 30 seconds in 30 normal subjects. For these normal subjects, ipsilateral adaptation always exceeded contralateral adaptation, although differences between the two conditions were not significant. In addition, contralateral and ipsilateral acoustic reflex adaptation of four subjects with varying degrees of sensorineural hearing loss were compared to the normative data. Results for these impaired ears indicated that a longer period of activation may be necessary to distinguish between normal reflex adaptation and adaptation which may occur in cochlear pathology. Further, in three normal ears and two ears with cochlear pathology, ipsilateral adaptation equaled or exceeded 50% of the initial value within 10 seconds of activation. This finding suggests that the same criterion which is used for establishing abnormal contralateral adaptation cannot be used for abnormal ipsilateral adaptation.