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.

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.