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Auditory Brainstem Responses at 6 and 8 kHz in Infants With Normal Hearing.

PURPOSE
Normative auditory brainstem response (ABR) data for infants and young children are available for 0.25-4 kHz, limiting clinical assessment to this range. As such, the high-frequency hearing sensitivity of infants and young children remains unknown until behavioral testing can be completed, often not until late preschool or early school ages. The purpose of this study was to obtain normative ABR data at 6 and 8 kHz in young infants.


METHOD
Participants were 173 full-term infants seen clinically for ABR testing at 0.4-6.7 months chronological age (M = 1.4 months, SD = 1.0), 97% of whom were ≤ 12 weeks chronological age. Stimuli included 6 and 8 kHz tone bursts presented at a rate of 27.7/s or 30.7/s using Blackman window gating with six cycles (6 kHz) or eight cycles (8 kHz) rise/fall time and no plateau. Presentation levels included 20, 40, and 60 dB nHL. The ABR threshold was estimated in 5- to 10-dB steps.


RESULTS
As previously observed with lower frequency stimuli, ABR waveforms obtained in response to 6 and 8 kHz tone bursts decreased in latency with increasing intensity and increasing age. Latency was shorter for 8-kHz tone bursts than 6-kHz tone bursts. Data tables are presented for clinical reference for infants ≤ 4 weeks, 4.1-8 weeks, and 8.1-12 weeks chronological age including median ABR latency for Waves I, III, and V and the upper and lower boundaries of the 90% prediction interval. Interpeak Latencies I-III, III-V, and I-V are also reported.


CONCLUSION
The results from this study demonstrate that ABR assessment at 6 and 8 kHz is feasible for young infants within a standard clinical appointment and provide reference data for clinical interpretation of ABR waveforms for frequencies above 4 kHz.