OBJECTIVETo estimate tone-pip auditory brainstem response (tone-pip ABR) and auditory steady-state response (ASSR) thresholds to follow the development of hearing in four groups of normal babies through the first 6 month of life and to make a comparison between the tone-pip ABR and ASSR for 0.25 - 8 kHz frequency range at different groups.

METHODSThe tone-pip ABR and ASSR were recorded in four groups of normal hearing infants (160 ears) at the age of 2 - 4 day, 6 weeks, 3-month and 6-month. Tone-pip ABR and ASSR thresholds were established in 0.25, 0.5, 1, 2, 4 and 8 kHz stimuli.

RESULTSFor click ABR, the wave latency of I, III, V and inter-wave latency of I-III, III-V and I-V decreased as the age increase. The developmental changes were obvious in wave I and III before 6 weeks and 3 months respectively. Tone-pip ABR had the similar waveform as the click ABR. With the frequency increasing, their waveforms and wave latencies of I, III and V were getting better and shorter respectively. There was significant difference between the thresholds of tone-pip ABR and ASSR (all P < 0.05). The tone-pip ABR thresholds were significantly lower than those of ASSR from 0.5 to 8 kHz. Both ASSR and tone-pip ABR had similar audiograms for different age of infants with normal hearing.

CONCLUSIONSThe longitudinal findings presented in this study suggest that with the maturational development, the wave latency of I, III, V and inter-wave latency of I-III, III-V and I-V of tone-pip ABR decrease as the age increase, while the hearing sensitivity have no changes. Both tone-pip ABR and ASSR have stable frequency specificity. Compared to the ASSR, tone-pip ABR have lower response threshold and maybe nearer to the hearing level of the infant.