Objective assessment of frequency-specific hearing thresholds in babies

OBJECTIVE: To report on clinical experience using dichotic multiple-stimulus auditory steady-state responses (ASSRs) as an objective technique to estimate frequency-specific hearing thresholds in hearing-impaired infants. METHODS: A comparison was made between the click-evoked auditory brainstem response (ABR), auditory steady-state responses and behavioral hearing thresholds (BHTs). Both ears of 10 infants between 3 and 14 months of age were tested. ABR and ASSRs were recorded during the same test session. ABR was evoked by 100 micros clicks. ASSRs were evoked by amplitude- and frequency-modulated tones with carrier frequencies of 0.5, 1, 2 and 4 kHz and modulation frequencies ranging from 82 to 110 Hz. Eight signals (four to each ear) were presented simultaneously. ASSR thresholds were derived after separate recordings of approximately 5, 7.5 and 10 min to compare the influence of test duration. BHTs were defined in later test sessions as soon as possible after the ASSR test, dependent on medical and developmental factors. RESULTS: For the subjects tested in this study 60% of ABR thresholds and 95% of ASSR thresholds for 1, 2 and 4 kHz were found at an average age of 7 months. Only 51% of frequency-specific BHTs could be obtained but on average 5 months later. The correlation of ABR thresholds and ASSR thresholds at 2 kHz was 0.77. The correlation of ASSRs and BHTs was 0.92. The mean differences and associated standard deviations were 4 +/- 14, 4 +/- 11, -2 +/- 14 and -1 +/- 13 dB for 0.5, 1, 2 and 4 kHz, respectively. The average test duration was 45 min for ABR (one threshold in both ears) and 58 min for ASSR (four thresholds in both ears). By reducing the duration of the separate recordings of ASSR, the precision of the hearing threshold estimate decreased and the number of outlying and missing values increased. Correlation coefficients were 0.92, 0.89 and 0.83 for recordings of maximum 10, 7.5 and 5 min, respectively. A compromise between test duration and precision has to be sought. CONCLUSIONS: Multiple-frequency ASSRs offer the possibility to estimate frequency-specific hearing thresholds in babies in a time-efficient way.     

Aided auditory steady-state responses in infants

Infants with hearing loss routinely receive hearing aids several months before reliable behavioral responses to amplified sound can be observed. This necessitates objective measures to validate hearing-aid fittings. A single report has demonstrated the use of ASSRs to determine aided thresholds in children but data in young infants is still lacking. The current study explored aided ASSR compared to unaided ASSR thresholds and subsequent behavioral thresholds in a group of six young infants with hearing loss who received hearing aids between three and six months of age. Aided ASSR thresholds were obtained in 83% of frequencies where aided behavioral thresholds were obtained, with a mean threshold difference of 13+/-13 dB. The aided ASSR-based threshold estimates were within 15 dB of behavioral thresholds in 63% of cases, indicating a moderate correlation (r = 0.55). Comparing aided and unaided ASSR measurements revealed an average functional gain of 36+/-15 dB. These results indicate that ASSRs can provide the first evidence of robust hearing aid benefit in young infants several months before behavioral responses are observed.     

Aided auditory steady-state responses in infants

Infants with hearing loss routinely receive hearing aids several months before reliable behavioral responses to amplified sound can be observed. This necessitates objective measures to validate hearing-aid fittings. A single report has demonstrated the use of ASSRs to determine aided thresholds in children but data in young infants is still lacking. The current study explored aided ASSR compared to unaided ASSR thresholds and subsequent behavioral thresholds in a group of six young infants with hearing loss who received hearing aids between three and six months of age. Aided ASSR thresholds were obtained in 83% of frequencies where aided behavioral thresholds were obtained, with a mean threshold difference of 13±13 dB. The aided ASSR-based threshold estimates were within 15 dB of behavioral thresholds in 63% of cases, indicating a moderate correlation (r = 0.55). Comparing aided and unaided ASSR measurements revealed an average functional gain of 36±15 dB. These results indicate that ASSRs can provide the first evidence of robust hearing aid benefit in young infants several months before behavioral responses are observed.     

Prognostic validity of dichotic multiple frequencies auditory steady-state responses versus distortion product otoacoustic emissions in hearing screening of high risk neonates

Objective

To determine the validity of dichotic multiple frequencies auditory steady-state responses (ASSR) as a hearing screening technique versus using distortion product otoacoustic emissions (DPOAEs) among high-risk neonates.

Methods

A cross sectional study was performed on 118 high-risk neonates by means of dichotic multiple frequencies ASSR and DPOAE for hearing screening. DPOAE results were used as the standard for hearing screening in parallel with ASSR. Dichotic multiple frequencies ASSR results were analyzed by means of F-value of less or greater than 0.05 criteria as a pass-fail for the responses. Dichotic multiple ASSR hearing screening technique was considered in two intensity levels at 40 and 70 dB HL. The ASSRs thresholds were measured in high risk neonates with and without hearing deficits as determined by DPOAES. The results of ASSR and DPOAE were compared to be gathered by contingency table in order to obtain sensitivity, specificity and other different statistical values. Average performing times for the tests were analyzed.

Results

The specificity of dichotic multiple ASSR was 92.6%, 93.8% and the sensitivity was 71.6%, 62.2% at the 70 and 40 dB hearing levels, respectively. Mean ASSR thresholds for normal-hearing infants at an average corrected age of 6 days were 32.2 ± 12.2, 29.8 ± 10.2, 26.2 ± 11.4 and 30.4 ± 10.8 dB HL for 0.5, 1, 2 and 4 kHz, respectively. The average times for performing the tests were 18.7 and 32.9 min respectively.

Conclusions

ASSR with this special paradigm is a fairly desirable method for hearing screening of high-risk neonates. There is good concordance between ASSRs and DOPAEs results among high risk neonates referred for hearing screening. The sensitivity and specificity of this test is sufficient for hearing screening in high risk neonates. This test could be valuable for rapid confirmation of normal thresholds. As long as further research have not been conducted on ASSR, great caution should be made to interpret the results of ASSR as a hearing screening technique in young infants and also additional techniques such as the tone-evoked ABRs should be used to cross-check results. It's still too soon to recommend ASSRs as a standalone electrophysiologic measure of hearing thresholds in infants.     

Hearing assessment by recording multiple auditory steady-state responses: the influence of test duration

The influence of test duration on the precision of hearing thresholds estimated by recording multiple auditory steady-state responses (ASSRs) was investigated. ASSR thresholds at four frequencies in both ears were assessed in 10 normal-hearing and 10 hearing-impaired subjects. The precision of the estimated hearing thresholds was compared for ASSR recordings of 5, 10 and 15 min per intensity level, corresponding to total test durations of approximately 30, 55 and 70 min for hearing-impaired ears. Furthermore, an intensity step size of 10 dB was compared to a step size of 5 dB. The mean difference scores averaged over the four frequencies were 15 +/- 10, 12 +/- 9 and 11 +/- 8 dB after recordings of 5, 10 and 15 min respectively. The corresponding Pearson correlation coefficients were 0.93, 0.95 and 0.96. Increasing the length of the separate recordings increases the precision of the estimates, independent of tested frequency. A compromise between both will have to be made. With a total test duration of approximately 1 h, four hearing thresholds in both ears can be estimated with a standard error of the estimate of 8 dB.     

Multiple auditory steady-state responses in children and adults with normal hearing, sensorineural hearing loss, or auditory neuropathy

OBJECTIVES: We tested the clinical effectiveness of multiple auditory steady-state responses (ASSRs) for the objective assessment of hearing thresholds in patients with and without hearing loss, candidates for cochlear implants, and children with auditory neuropathy. METHODS: The study sample included 29 subjects with sensorineural hearing loss (SNHL), 18 candidates for cochlear implants, 11 subjects with auditory neuropathy, and 18 subjects with normal hearing thresholds. Behavioral hearing thresholds and ASSRs to carrier frequencies of 0.5, 1, 2, and 4 kHz were obtained. Special care was taken to minimize possible aliasing and high-intensity multiple stimulation effects. Differences and correlations between the ASSRs and the behavioral thresholds were determined. RESULTS: The ASSR estimation of behavioral thresholds in the normal-hearing group was elevated, whereas very close predictions were found for the SNHL group. The correlations between the two measures ranged from 0.86 at 0.5 kHz carrier frequency to 0.94 at 2 kHz. In the cochlear implant candidates and the auditory neuropathy group, the ASSR thresholds generally overestimated the behavioral audiogram. In these groups the number of detected ASSRs was higher than the number of behavioral responses, especially for the high-frequency carrier stimuli. CONCLUSIONS: Multiple ASSRs may reliably predict the behavioral threshold in subjects with SNHL and may serve as a valuable objective measure for assessing the hearing threshold across different frequencies in candidates for cochlear implants and children with auditory neuropathy.     

Thresholds determined using the monotic and dichotic multiple auditory steady-state response technique in normal-hearing subjects

Auditory steady-state responses (ASSRs) were elicited by presenting single or multiple, 77-105 Hz amplitude-modulated 0.5, 1, 2, and 4 kHz tones to one or both ears. Objectives of this study were to (i) replicate and extend previous multiple ASSR studies in a quiet double-walled sound booth, and (ii) discover differences (if any) between thresholds assessed in monotic and dichotic conditions, which ranged between 15 and 22dB SPL. The present study's behavioural and ASSR thresholds are 0-10 dB lower (better) than results of previous monotic studies. Further, there are no significant differences in ASSR thresholds between dichotic and monotic stimulus conditions. Therefore, dichotic multiple AM tone stimulation does not produce a change in the ASSR that affects threshold estimation in a clinically significant manner. Thus, at least for detecting normal hearing, the dichotic multiple ASSR technique is a feasible method for estimating hearing thresholds that would substantially reduce recording time compared to conventional single-stimulus techniques.     

Estimations of auditory sensitivity for young cochlear implant candidates using the ASSR: preliminary results

This paper presents preliminary results obtained with the use of the auditory steady-state response (ASSR) technique as part of a cochlear implant candidacy assessment protocol for infants Fifteen infants (30 ears), between 10 and 60 months of age, with severe-to-profound hearing loss participated in the study. ASSR measurements were performed for 0.5, 1, 2 and 4kHz at intensities up to 120-128dB HL. The ASSR thresholds were obtained in 74%, of the measurements, and exceeded the maximum auditory brainstem response (ABR) intensity output in 91% of cases and the maximum free-field behavioral intensity output in 84% of cases. Eighty-seven per cent of ASSR threshold measurements were measured at intensities of 100dB HL or higher, and almost half (47%) were measured at intensities of 115 dB HL and higher. Preliminary results indicate that absent ABR and behavioral thresholds do not preclude the possibility of residual hearing, making the ASSR a primary source of information regarding profound levels of hearing loss.     

Estimations of auditory sensitivity for young cochlear implant candidates using the ASSR: preliminary results

This paper presents preliminary results obtained with the use of the auditory steady-state response (ASSR) technique as part of a cochlear implant candidacy assessment protocol for infants. Fifteen infants (30 ears), between 10 and 60 months of age, with severe-to-profound hearing loss participated in the study. ASSR measurements were performed for 0.5, 1, 2 and 4 kHz at intensities up to 120–128 dB HL. The ASSR thresholds were obtained in 74% of the measurements, and exceeded the maximum auditory brainstem response (ABR) intensity output in 91% of cases and the maximum free-field behavioral intensity output in 84% of cases. Eighty-seven per cent of ASSR threshold measurements were measured at intensities of 100 dB HL or higher, and almost half (47%) were measured at intensities of 115 dB HL and higher. Preliminary results indicate that absent ABR and behavioral thresholds do not preclude the possibility of residual hearing, making the ASSR a primary source of information regarding profound levels of hearing loss.     

Auditory steady-state responses for children with severe to profound hearing loss

OBJECTIVE: To investigate the clinical usefulness of the dichotic single-frequency auditory steady-state response (ASSR) for estimation of behavioral thresholds in children with severe to profound congenital sensorineural hearing loss. DESIGN: A comparative experimental research design was selected to compare behavioral and ASSR thresholds for the sample. Behavioral pure-tone audiometry served as the criterion standard. SETTING: Hearing Clinic, Department of Communication Pathology, University of Pretoria, Pretoria, South Africa. PATIENTS: A referred sample of 10 patients (20 ears), 5 girls and 5 boys aged 10 to 15 years (mean age, 13 years 4 months), with severe to profound sensorineural hearing impairment. MAIN OUTCOME MEASURES: The difference, and correlation, between 160 pure-tone behavioral and ASSR thresholds at 0.5, 1, 2, and 4 kHz. RESULTS: Mean differences between ASSR and behavioral thresholds were 6 dB for 0.5 kHz and 4 dB for 1, 2, and 4 kHz, with standard deviations varying between 8 and 12 dB. No significant differences (P<.05) were observed between ASSR and behavioral thresholds, except at 0.5 kHz, and Pearson correlation coefficients varied between 0.58 and 0.74 across the evaluated frequencies, with best correlation at 1 kHz and worst at 0.5 kHz. CONCLUSIONS: The ASSR thresholds provided reliable estimations of behavioral thresholds for children with severe to profound hearing loss and indicated an increased sensitivity for more profound hearing loss.     

Brain stem and cortical mechanisms underlying the binaural masking level difference in humans: an auditory steady-state response study

OBJECTIVE: The behavioral binaural masking level difference (BMLD) is believed to reflect brain stem processing. However, this conflicts with transient auditory evoked potential research that indicates the auditory brain stem and middle latency responses do not demonstrate the BMLD. The objective of the present study is to investigate the brain stem and cortical mechanisms underlying the BMLD in humans using the brain stem and cortical auditory steady-state responses (ASSRs). DESIGN: A 500-Hz pure tone, amplitude-modulated (AM) at 80 Hz and 7 (or 13) Hz, was used to elicit brain stem and cortical ASSRs, respectively. The masker was a 200-Hz-wide noise centered on 500 Hz. Eleven adult subjects with normal hearing were tested. Both ASSR (brain stem and cortical) and behavioral thresholds for diotic AM stimuli (when the signal and noise are in phase binaurally: SoNo) and dichotic AM stimuli (when either the signal or noise is 180 degrees out-of-phase between the two ears: SpiNo, SoNpi) were investigated. ASSR and behavioral BMLDs were obtained by subtracting the threshold for the dichotic stimuli from that for the diotic stimuli, respectively. Effects for modulation rate, signal versus noise phase changes, and behavioral versus ASSR measure on the BMLD were investigated. RESULTS: Behavioral BMLDs (mean = 8.5 to 10.5 dB) obtained are consistent with results from past research. The ASSR results are similar to the pattern of results previously found for the transient auditory brain stem responses and the N1-P2 cortical auditory evoked potential, in that only the cortical ASSRs (7 or 13 Hz) demonstrate BMLDs (mean = 5.8 dB); the brain stem ASSRs (80 Hz) (mean = 1.5 dB) do not. The ASSR results differ from the previous transient N1-P2 studies, however, in that the cortical ASSRs show a BMLD only when there is a change in the signal interaural phase, but not for changes of noise interaural phase. CONCLUSIONS: Results suggest that brain processes underlying the BMLD occur either in a different pathway or beyond the brain stem auditory processing underlying the 80-Hz ASSR. Results also suggest that the cortical ASSRs have somewhat different neural sources than the transient N1-P2 responses, and that they may reflect the output of neural populations that previous research has shown to be insensitive to binaural differences in noise.     

Establishing normal hearing with the dichotic multiple-frequency auditory steady-state response compared to an auditory brainstem response protocol

OBJECTIVE: To determine the clinical usefulness of the dichotic multiple-frequency (MF) auditory steady-state response (ASSR) technique for estimating normal hearing compared to a 0.5-kHz tone burst and broadband click auditory brainstem response (ABR) protocol in a sample of adults. MATERIAL AND METHODS: A comparative experimental research design was selected in order to compare estimations of normal hearing obtained with the dichotic ASSR technique at 0.5, 1, 2 and 4 kHz with a 0.5-kHz tone burst and broadband click ABR protocol. The recording times required for each procedure were also compared. Normal-hearing subjects (n = 28) were selected according to immittance values within normal limits and pure-tone behavioural thresholds of < 25 dB HL across frequencies. RESULTS: The dichotic MF ASSR estimated normal hearing to be, on average, 30-34 dB HL across the range 0.5-4 kHz. The mean estimate of normal hearing for 0.5 kHz using tone burst ABRs was 30 dB nHL and the mean click ABR threshold was 16 dB nHL, i.e. 14-18 dB better than the ASSR thresholds. The dichotic MFASSR technique recorded 8 thresholds (4 in each ear) in a mean time of 23 min. The ABR protocol recorded 4 thresholds (2 in each ear) in a mean time of 25 min. CONCLUSION: Both the dichotic MF ASSR and ABR protocols provided a time-efficient estimation of normal hearing. There was no significant difference between the tone burst ABR and MF ASSR techniques in terms of estimation of normal hearing at 0.5 kHz. The dichotic MF ASSR technique proved more time-efficient by determining more thresholds in a shorter time compared to the ABR protocol.     

声场中记录的听性稳态助听反应阈与行为测试助听听阈的相关性

目的 应用多频听觉稳态反应(ASSR)Chirp刺激信号在声场中测试助听反应阈,观察其阈值与行为测试助听听阈的相关性,探讨多频听觉稳态反应Chirp刺激信号声场测试评估助听器补偿效果的临床意义.方法 选取22例(39耳)重度感音神经性听力损失、已配戴助听器的患儿(听障组)和16例(32耳)听力正常儿童(对照组)为研究对象.应用国际听力Eclipse EP25型多频稳态诱发电位仪及美国GSI-61型听力计,分别对听障组在声场中使用两种仪器测试助听听阈;对对照组进行裸耳行为听阈与声场中听觉稳态反应阈测试.结果 在0.5、1、2、4 kHz处,听障组ASSR助听反应阈与行为助听听阈的相关系数分别为0.65、0.68、0.77和0.82,P值均<0.01,显示两种测试结果有相关性;对照组裸耳行为听阈与声场中记录的听觉稳态反应阈在0.5、1、2、4 kHz配对t检验均呈显著差异(P<0.01),ASSR声场反应阈高于行为听阈20～30 dB HL.结论 应用多频听觉稳态反应Chirp刺激信号声场测试进行助听器补偿效果评估在临床上具有可行性.     

Hearing assessment by recording multiple auditory steady-state responses: the influence of test duration

The influence of test duration on the precision of hearing thresholds estimated by recording multiple auditory steady-state responses (ASSRs) was investigated. ASSR thresholds at four frequencies in both ears were assessed in 10 normal-hearing and 10 hearing-impaired subjects. The precision of the estimated hearing thresholds was compared for ASSR recordings of 5, 10 and 15 min per intensity level, corresponding to total test durations of approximately 30, 55 and 70 min for hearing-impaired ears. Furthermore, an intensity step size of 10 dB was compared to a step size of 5 dB. The mean difference scores averaged over the four frequencies were 15±10, 12±9 and 11±8 dB after recordings of 5, 10 and 15 min respectively. The corresponding Pearson correlation coefficients were 0.93, 0.95 and 0.96. Increasing the length of the separate recordings increases the precision of the estimates, independent of tested frequency. A compromise between both will have to be made. With a total test duration of approximately 1 h, four hearing thresholds in both ears can be estimated with a standard error of the estimate of 8dB.     

The auditory steady-state response: comparisons with the auditory brainstem response

Two studies are reported in which the threshold estimates from auditory steady-state response (ASSR) tests are compared to those of click- or toneburst-evoked auditory brainstem responses (ABRs). The first, a retrospective review of 51 cases, demonstrated that both the click-evoked ABR and the ASSR threshold estimates in infants and children could be used to predict the pure-tone threshold. The second, a prospective study of normal-hearing adults, provided evidence that the toneburst-evoked ABR and the modulated tone-evoked ASSR thresholds were similar when both were detected with an automatic detection algorithm and that threshold estimates varied with frequency, stimulus rate, and detection method. The lowest thresholds were obtained with visual detection of the ABR. The studies illustrate that ASSRs can be used to estimate pure-tone threshold in infants and children at risk for hearing loss and also in normal-hearing adults.     

Determining the upper limits of stimulation for auditory steady-state response measurements

OBJECTIVE: To determine the maximum stimulus levels at which a measured auditory steady-state response (ASSR) can be assumed to be a reliable measure of auditory thresholds. DESIGN: ASSR thresholds were measured at octave frequencies from 500 to 4000 Hz in 10 subjects with profound hearing loss. These subjects provided no behavioral responses to sound at the limits of pure-tone audiometers and at the limits of the stimulus levels produced by the ASSR device. Subjects were divided into two groups of five, with repeated measures obtained within the same session in one group and repeated measures obtained in a separate session on a different day in the other group. RESULTS: ASSR thresholds were observed in all 10 subjects at each of four frequencies and in both trials. On average, these ASSR thresholds were observed at 100 dB HL (SD = 5 dB). Because these responses were at least 18 to 22 dB below the limits of the equipment where all subjects had no behavioral responses, it is reasonable to conclude that the ASSRs were not generated by the auditory system. CONCLUSIONS: An artifact or distortion may be present in the recording of ASSRs at high levels. These data bring into question the view that there is a wider dynamic range for ASSR measurements compared with auditory brain stem response measurements, at least with current implementation.     

Evaluation of residual hearing in cochlear implants candidates using auditory steady-state response

Conclusion: The correlations between behavioral and auditory steady-state response (ASSR) thresholds were significant at 500, 1000, 2000, and 4000 Hz. ASSR presented high sensitivity and specificity in the detection of residual hearing in cochlear implant candidates when compared with warble-tone audiometry. Objectives: To assess residual hearing in cochlear implant candidates by comparing the electrophysiological thresholds obtained in dichotic single-frequency ASSR with behavioral thresholds at 500, 1000, 2000, and 4000 Hz. Methods: This was a comparative study between ASSR and warble-tone audiometry thresholds in 40 cochlear implant candidates (80 ears) before cochlear implantation with bilateral severe-to-profound sensorineural hearing loss. Results: Thresholds were obtained in 62.5% of all frequencies evaluated in warble-tone audiometry and in 63.1% in the ASSR. ASSR sensitivity was 96% and specificity was 91.6%. Mean differences between behavioral and ASSR thresholds did not reach significance at any frequencies. Strong correlations between behavioral and ASSR thresholds were observed in 500, 1000, and 2000 Hz and moderate in 4000 Hz, with correlation coefficients varying from 0.65 to 0.81. On 90% of occasions, ASSR thresholds were acquired within 10 dB of behavioral thresholds.     

正常听力成人骨导听性稳态反应的研究

目的①通过正常听力成人乳突和耳后听性稳态反应（auditory steady--state response,ASSR）测试信号行为阈值的测试,研究骨振器位置与反应阈的关系并建立该信号骨导的正常听力级;②通过单频及多频刺激方式骨导ASSR的反应幅值及阈值的比较,研究刺激方式对骨导ASSR的影响。方法ASSR测试信号为0．5、1、2、4kHz短音（0．5kHz的上升／下降时间为4ms,1、2和4kHz为2ms,无平台）,其重复速率分别为77、87、93、101Hz,经B71骨振器给出。将正常听力成人分为两组,实验1组（30人）,分别记录0．5、1、2、4kHz ASSR测试信号在乳突、耳后的骨导行为阈值;实验2组（12人）,分别采用单、多频刺激方式,记录其0．5、1、2、4kHz的反应阈以及刺激强度为50dBnHL时的反应幅值。结果①骨振器位于乳突与耳后的骨导行为阈值无显著性差异,0．5、1、2、4kHz的骨导行为反应阈分别为62．6&#177;4．8、47．1&#177;4．8、46．8&#177;6．2、32．4&#177;5．1dB re：1μN（ppe）,取该反应阈的均值作为本研究所使用信号的骨导正常听力级,记作0dBnHL;②在刺激强度为50dBnHI。时,不同刺激方式间反应幅值差异有显著统计学意义;③单、多频刺激方式间骨导ASSR阈值差异无统计学意义,0．5、1、2、4kHz阈值分别为96．7&#177;9．7、70．3&#177;11．6、60．6&#177;7．4、52．8&#177;7．2dBr e：1μN（ppe）,各频率间差异有显著统计学意义。结论①骨振器位于乳突与耳后对行为阈值没有显著性影响;②在刺激强度为50dB nHL时,单、多频刺激方式的反应幅值差异有显著统计学意义;③单、多频刺激方式下,骨导ASSR阈值差异无统计学意义。     

Normal ipsilateral/contralateral asymmetries in infant multiple auditory steady-state responses to air- and bone-conduction stimuli

OBJECTIVES: Two-channel recordings of infants' air- and bone-conduction auditory brainstem responses to brief tones show ipsilateral and contralateral (to the stimulated ear) asymmetries which may be used to isolate which cochlea is the primary contributor to the response. The objective of this study was to determine whether similar ipsilateral/contralateral asymmetries are also present in the air- and bone-conduction "brainstem" (77 to 101 Hz) auditory steady-state responses (ASSRs) of infants. DESIGN: Two-channel ASSRs were recorded in infants (2 to 11 mo) and adults (18 to 40 yr) with normal hearing. Multiple stimuli (carrier frequencies: 500 to 4000 Hz; amplitude/frequency modulated) were presented using a B-71 oscillator on the temporal bone or an ER3-A insert earphone. Bone-conduction ASSR amplitudes, phase delays, and thresholds were obtained for the electroencephalographic (EEG) channels ipsilateral and contralateral to the oscillator temporal-bone placement. Bone-conduction ASSRs were also obtained to the stimulus presented to the opposite temporal bone (at 40 dB HL only). Air-conduction ASSR amplitudes and phase delays were obtained at 60 dB HL in each ear for the EEG channels ipsilateral and contralateral to the transducer. RESULTS: Infants showed more ipsilateral/contralateral asymmetries in both air- and bone-conduction ASSRs compared with adults. Mean bone-conduction ASSR thresholds in infants were 13 to 15 dB higher (i.e., poorer) in the contralateral EEG channel compared with the ipsilateral EEG channel for 500 to 4000 Hz. In adults, there were no large differences (i.e., within 1 dB) between ipsilateral and contralateral ASSR thresholds. Based on ipsilateral/ contralateral threshold differences in infants, interaural attenuation for bone-conducted stimuli was estimated to be at least 10 to 30 dB for most infants. In contrast, most adults showed little interaural attenuation for bone-conducted stimuli. ASSR amplitudes are larger and phase delays are shorter in the ipsilateral EEG channel. For infants, the difference in air-conduction ASSR amplitude between EEG channels was twice that observed for adults. Infants also had greater ASSR amplitude differences between EEG channels for bone-conduction stimuli compared with adults, but the difference was less than that seen for air-conduction stimuli. For air-conduction stimuli, infants had significantly longer phase delays in the contralateral EEG channel compared with the ipsilateral EEG channel. Adults showed no significant differences in air-conduction ASSR phase delay between EEG channels. For bone-conduction stimuli, both infants and adults had significantly longer phase delays in the contralateral EEG channel compared with the ipsilateral EEG channel; the differences in ASSR phase delays between EEG channels were much smaller in infants compared with adults and fewer adults had absent responses in the contralateral EEG channels compared with infants (12% versus 34%). When the transducers were switched to the opposite ear/mastoid, the infant and adult ipsilateral/contralateral asymmetries also switched. CONCLUSIONS: Ipsilateral/contralateral asymmetries in air- and bone-conduction ASSRs are clearly present more often and are larger in infants compared with adults. Our findings also suggest that most infants have at least 10 to 30 dB of interaural attenuation to bone-conducted stimuli. These asymmetries in the bone-conduction ASSR have potential as a clinical tool for isolating the cochlea that is contributing to the response in infants.