Comments on 'Auditory brainstem responses to middle- and low-frequency tone pips'

This article contains critical comments on data described in a recent paper dealing with differences between click- and tone-pip-evoked auditory brainstem responses (ABR) by Maurizi et al. [Audiology 23: 75-84, 1984]. The primary criticism relates to the lack of validity of comparing ABR obtained with different input filter settings. When utilizing identical input filter settings, click- and tone-pip-evoked brainstem responses exhibit similar morphologies: both consist of a slow vertex-positive wave with faster superimposed vertex-positive components.     

Auditory brainstem response (ABR) to tone pips in hearing-impaired children

The correspondence between ABR thresholds to tone pips and behavioral thresholds at 500, 1000 and 2000 Hz was studied in 13 normal and 55 hearing-impaired children, including 42 sensori-neural losses and 13 conductive losses. The children's ages ranged from 1 year 3 months to 8 years. Tone pips were provided with 2-cycle rise-fall times and 2-cycle plateaus. The correlations between the two measures were highly significant at 3 frequencies both in sensori-neural losses and conductive losses. In the subjects with sensori-neural losses, the ABR thresholds tended to be lower than the behavioral thresholds. Mean threshold differences between the ABR and behavioral audiometry at each frequency in sensori-neural losses were 1.6, 0.26 and 5.8 dB, respectively. On the other hand, in the subjects with conductive losses, the ABR thresholds were higher than the behavioral ones by 9.6, 7.8 and 7.5 dB at respective frequencies. Therefore, the hearing acuity in young children with sensori-neural losses can be predicted with accuracy from the ABR thresholds to tone-pips at 500, 1000 and 2000 Hz.     

Auditory brainstem responses to tone bursts in normally hearing subjects

Auditory brainstem responses were recorded from 20 normally hearing subjects using tone-burst stimuli that were gated with cosine-squared functions. Clear responses were observed over a wide range of frequencies and levels. These responses were highly reproducible within individual subjects and were reliably measured by two independent examiners. ABR thresholds were higher than behavioral thresholds for all frequencies, especially for lower frequencies. Intersubject variability also was greater for lower frequencies. Wave-V latencies decreased with increases in both frequency and level for frequencies from 250 to 8000 Hz and for levels from 20 to 100 dB SPL. The standard deviations seldom exceeded 10% of the mean wave-V latency for any combination of level and frequency. These latencies can be viewed as the sum of both a peripheral and a central component. Assuming that the central component is relatively independent of both frequency and level, changes of wave V latency must be related to peripheral factors, such as travel time along the cochlear partition, and to stimulus characteristics, such as rise time.     

Effects of high-pass filtering on the waveform and threshold of auditory brainstem responses to tone pips

The authors answer to the comments on their paper 'Auditory Brainstem Responses to middle-and low-frequency tone pips' by Dr. Paul Kileny. Physical characteristics of the stimuli employed, waveform and latency variations using different high-pass filtering (50 and 200 Hz) are discussed.     

40 Hz middle latency responses to low frequency tone pips in normally hearing adults

Middle latency auditory evoked potentials can be rapidly obtained using a 40/second stimulous rate, taking advantage of response periodicity to accelerate the averaging procedure. This technique was used in 31 normally hearing adults for low frequency response evaluation. Tone pips at 250, 500, and 1000 Hz were employed. The average difference between the middle latency evoked potential threshold and the subjective threshold was 17.9 dB at 250 Hz, 14.5 dB at 500 Hz, and 13 dB at 1000 Hz. The waveform of the response and the latency and amplitude of its main peaks were also analyzed. Thresholds at 500 and 1000 Hz were also determined using brainstem evoked responses in 15 of the subjects. These differed, on average, by 30 dB from subjective thresholds. The 40 Hz MLR paradigm thus appears to be an accurate and rapid method for low frequency threshold evaluation in adults, but it is greatly influenced by the state of arousal. During sleep, response amplitude decreases and threshold increases by about 15 dB. This may be of great concern when interpreting the results in children, in whom low frequency threshold evaluation is of primary importance.     

Auditory brainstem responses in perinatal asphyxia

Averaged auditory brainstem responses (ABR) elicited by unfiltered clicks were recorded from 14 asphyxiated neonates with clinical evidence of CNS suppression at 3–17 days of age, and from a group of healthy neonates matched in gestation period and weight. Statistically significant differences were found between the two groups in several ABR parameters and characteristics. In general, longer ABR component latencies and interwave intervals were the rule in the asphyxiated group. Short-term follow-up of the asphyxiated infants suggested that the ABR is sensitive to recovery trends from hypoxic encephalopathy. The results of a 6-month follow-up are also summarized. The results are discussed with regard to the histopathological and experimental information available from current literature.     

Auditory brainstem responses and behavioural responses in pre-term infants

Auditory brainstem responses (ABRs) and behavioural thresholds were studied in 25 pre-term infants with post-conceptional ages of approximately 40 weeks to ascertain whether there were differences in the ABR between normal preterm and full-term new born infants to compare behavioural thresholds around 40 weeks of post-conceptional age and to follow changes of their behavioural thresholds in the first year of life. ABR thresholds, peak latencies of Waves I and V and the I-V peak interwave latency were measured. Behavioural audiometric thresholds to pure tones were determined through behavioural observation audiometry and conditioned orientation-reflex audiometry. The ABR thresholds of the pre-term infants, whether they were small for date (SFD) or appropriate for date (AFD), were in the normal ranges of the controls. Moreover, there were no significant differences between either the SFD or the AFD group and controls, as far as Wave I or V latency or I-V interval are concerned. Thus, the ABR was apparently unaffected by the infant being small-for dates. Behavioural audiometry disclosed that all normal full-term infants responded to pure tone stimuli, with mean thresholds of 85 dB, while only 42% of AFD and 30% of SFD would respond to pure tone stimuli at 90 dB or less. Behavioural thresholds caught up with the normal range by 12 months of age, except for a few infants.     

Auditory brainstem and middle-latency responses in Bell's palsy

Patients with acute peripheral facial palsy (Bell's palsy) were examined by auditory brainstem response (ABR) and middle-latency response (MLR) for signs of brainstem involvement. ABR data on 30 patients indicated that wave V latencies were abnormal by greater than 3 SD in only 2 patients, 1 of whom showed abnormality contralateral to the affected side. When the criterion for abnormality was reduced to 2 SD, wave V abnormality was found in only 3 of the 30 patients. All 14 patients tested by MLR showed normal responses. These findings suggest that on the basis of evoked potential measures, brainstem involvement may not be pathognomonic of Bell's palsy.     

Auditory brainstem responses to tonal stimuli in young and aging rats

The auditory brain stem response (ABR) was studied in young adult and aged rats using 3,8 and 40 kHz tone pips. The expected inverse relationship between frequency and latency was observed in the younger group for waves I, II and III, while the response to the highest frequency stimulus had the longest latency at wave V. Absolute latencies for waves I through V each showed age-related increments with more pronounced changes occurring to 3 and 40 kHz stimuli than to the frequency of maximum sensitivity (8 kHz). Threshold increases with age for the highest frequency approximately doubled those for the lower frequencies. Examination of interpeak intervals (IPI) I-III, III-V and I-V revealed aging effects. The largest IPI I-V increment occurred to 3 kHz stimulation which reflects changes at both I-III and III-V sub-intervals. These results demonstrate electrophysiological correlates of aging due to transformations in the peripheral auditory system coupled with alterations in brainstem auditory pathways.     

Development of low-frequency tone burst versus the click auditory brainstem response

Often ABR threshold testing employs clicks to assess high-frequency hearing, and low-frequency tone bursts to assess low-frequency sensitivity. While a maturation effect has been shown for click stimuli, similar data are lacking for low-frequency toneburst stimuli. Thus, 305 infants ranging in conceptional age (CA) from 33 weeks to 74 weeks were tested. Absolute latencies were measured for wave V at 55, 35, and 25 dB nHL in response to a click and for wave V500 in response to a 500 Hz tone burst. Major wave latency in response to 500 Hz tone bursts decreases with age and do not stabilize by 70 weeks CA. Likewise, waves III and V latencies in response to clicks decrease with age, as has been reported by others, and do not stabilize by 70 weeks CA. Wave I latency produced by clicks did not decrease with age, being mature by 33 weeks CA.     

Hearing-aid-processed tone pips: electroacoustic and ABR characteristics

The auditory brainstem response (ABR) recorded while wearing a hearing aid may supply supplemental information about the benefit and appropriateness of the hearing aid for certain infants. The purposes of this study were (1) to determine the effects of different output limiting circuits on the acoustics of tone-pip stimuli used for ABR recordings and (2) assess how changes in hearing-aid-processed stimuli affect ABR characteristics. Electroacoustic input/output functions to tone-pip stimuli were constructed for three different output limiting circuits (wide dynamic range compression, output compression, and linear with peak clipping) available in a programmable hearing aid. Wave V latency and amplitude functions were then measured to the same stimuli and hearing aid settings in five normal-hearing adults. Electroacoustic results showed that none of the output limiting circuits, including linear peak clipping, were effectively activated by tone pips compared to the hearing aid performance to continuous tones. Aided wave V latency and amplitude functions were asymptotic to high stimulus levels, suggesting that cochlear output was in saturation.     

Auditory brain stem responses to high-frequency tone bursts in normal-hearing subjects

ABR and behavioral thresholds and ABR latencies were measured from six normal-hearing subjects in response to tone bursts, having frequencies of 9,000 to 16,000 Hz. In general, ABR thresholds were higher than behavioral thresholds; however, the differences were typically less than those observed for lower frequencies. Wave V latency-intensity functions were less dependent on frequency for these stimuli than they were for lower frequency stimuli. This may be due to the fact that higher frequencies are represented over a very narrow area of the cochlea and that minor variability in the measurement of latencies might obscure small differences in latency as a function of frequency. In general, these data suggest that ABRs can be measured in response to high-frequency stimuli and that these measurements may have clinical utility, especially when monitoring ototoxic effects in difficult-to-test patients.     

Auditory brainstem and middle latency responses in non-human primates

Auditory brainstem (ABR) and middle latency responses (MLR) were obtained from each ear in 8 crab-eating macaques, 4 white-handed gibbons, 4 siamangs and 2 orangutans. Macaques ranged in age from 5 days to 15 years with the 6 older animals in age-matched, male-female pairs. From each animal, latency-intensity functions were obtained and multiple MLR recordings were measured at 60 and 70 dB. Latency-intensity functions, interwave intervals, thresholds and percent detectability were calculated for ABR waveforms. Waves II and IV were largest in amplitude and were most consistently detected at low stimulus intensities in all species tested. Waves I and II had adult latencies in the youngest animal tested (5-day-old macaque), while waves III and IV were prolonged in comparison to the 15-month-old macaque, in whom latencies had reached adult values. There were no apparent sex differences in evoked potentials in the age-matched, male-female pairs. A broad, negative MLR at 7-13 ms was observed in all animals. Longer latency MLRs varied among animals of the same species, but were replicable in some individuals, including the youngest macaque (5 days) and orangutan (7 months). These data were compared to responses obtained in humans, other primates and other vertebrates.     

Auditory brainstem responses after radiotherapy for nasopharyngeal carcinoma

The effect of irradiation for nasopharyngeal carcinoma on auditory brainstem responses and hearing was investigated in 19 otologically normal patients undergoing standard fractionated megavoltage radiotherapy. Auditory brainstem responses and pure tone audiometry were performed before radiotherapy, and at 3 and 12 months after completion of radiotherapy. There were no significant changes in the wave I–III and III–V interpeak intervals, or in sensorineural hearing thresholds (bone conduction at 4 kHz and average of bone conduction at 0.5, 1, 2 and 4 kHz), after radiotherapy. In contrast to previous studies, we found no evoked potential evidence of subclinical brainstem damage arising from irradiation for nasopharyngeal carcinoma.     

Auditory brainstem responses in noise-induced permanent hearing loss

Fifty-four patients (108 ears) with presumed noise-induced hearing loss, were subjected to tonal and speech audiometry, impedance tests and measurements of auditory brainstem responses (ABR), in order to check for possible retrocochlear involvement. ABR data indicated that latency values of waves I, III and V, as well as III-I, V-III and V-I intervals fell within the normal range in all cases (M +/- 2 SD), even for fast repetition rates (51 stim/s). Poor waveform resolution of early components, particularly of wave I, was found in 12 ears (11.1%) and a total absence of evoked potentials not always related to the hearing loss, occurred in 5 ears (4.6%).     

Auditory brainstem evoked responses and attention. Contribution to a controversial subject

The clinical usefulness of the brainstem evoked response (BAER) derives from the high inter- and intra-subject reproducibility of V-wave latency. Attentiveness represents one possible cause of variation. To evaluate the effect of auditory or visual attention tasks and their repetition, we recorded BAERs during six repetitions of each of these two tasks. Each BAER was evoked by 2 000, 40 dB Hearing Level clicks. The results show that, at the 0.05 level, the difference in V-wave latency for auditory and for visual tasks is not significant. Moreover, repetition of the attention tasks fails to bring about any significant (p less than 0.05) change in this difference. In agreement with some researchers, but not with others, we show that attentiveness has little effect on BAER V-wave latency.     

Auditory brainstem responses of the cat: on- and off-responses

The auditory brainstem on- and off-responses evoked by tone and noise bursts have been studied in the cat. The number and amplitude of the off-response waves are proportional to the frequency specificity of the on-response, being greatest for the 4-kHz tone burst and smallest for the noise burst. The threshold of the 0.5-kHz off-response is lower than that of the on-response, but the amplitude of the former does not increase at higher stimulus levels. Derived-band studies show that at 4 kHz the on-and off-responses have identical frequency content, the 0.5-kHz off-response is restricted to the 2- to 8-kHz frequency band, while the noise burst off-response is entirely high frequency. The off-response is an on-response and is evoked by acoustic transients from the loudspeaker transducer.     

Auditory brainstem responses to single-slope stimuli. The influence of steepness and polarity

Click polarity has little influence on brainstem potentials. We applied an auditory stimulus similar to a step function generated in a closed acoustic system. The influence of stimulus onset steepness (comprising rise time and intensity) on wave V latency and amplitude was investigated. A remarkable latency prolongation was observed for condensation (C) compared with rarefaction (R), if a sharp bend at the foot of the slope was avoided. The C latency lag was nearly the amount of rise time. The effect can be explained by cochlear travel time. Wave V amplitude for R slopes was significantly enhanced. At high intensity and short rise time, it reached twice the values found with C slopes, or with clicks of either polarity. Although the explanations found are not yet satisfactory, a clinical application in cochlear diagnosis is predictable.