Abstract
The vertex-positive brain stem responses (BSR) to tone pips were recorded on 20 adult subjects with normal hearing. The overall frequency response of the amplifier system was 0.5 to 3000 Hz. No high-pass filter was used in the recording system. Tone pips at 500, 1000, 2000 and 4000 Hz with 2-cycle rise-decay times and one-cycle peak were delivered to the subjects at intervals of 75 msec. The BSR was detected in 53 to 73% of the tests at 10 dB SL and 89 to 100% at 20 dB SL. No significant difference was found in the response detectability between four test tones of 500 to 4000 Hz. Mean latency of the response as an inverse function of test frequency was proved to be linear and could be resolved into regression equations: y=4.56x+8.16 (10 dB SL), y=3.77x+7.76 (20 dB SL), y=2.81x+7.63 (30 dB SL), where y and x indicated a mean latency and one cycle duration of a test frequency, respectively. This result suggested that the responses were elicited through the regions on the basilar membrane proper to each nominal frequency. The detectability of the response in the present study differs from that of previous reports which showed a significant decrease in the detectability of the response at 500 Hz. The discrepancy of the results is very likely ascribable to a high-pass filter used in the recording system of the previous papers.