The effect of onset, offset and rise-decay times of tone bursts on brain stem response.

Auditory-evoked brain stem responses (BSRs) were recorded from the scalp in 4 cats and 10 human subjects. Auditory stimuli consisted of 1 kHz tone bursts and their duration, intensity and rise--decay time were varied. The BSR evoked by the tone bursts consisted of on- and off-responses. The off-responses showed different intensity--amplitude and different intensity--latency functions from the on-responses. In the feline subjects, an increase in rise time as an input resulted in an increase in the number of recorded sharp waves of the on-responses, indicating that several cycles of tone bursts during the rise time take part in generating on-responses. In both the feline and human subjects, BSRs were evoked by tone bursts with a rise time of as long as 10 msec; an increase in the rise time resulted in an increased latency and broadened waveforms of the on-responses. These demonstrated properties of BSR may provide useful information in determining input parameters, such as rise--decay time, appropriate for audiometric assessment.