Loss and recovery processes operative at the level of the cochlear microphonic during intermittent stimulation.

Abstract

It has become increasingly apparent that the ear's behavior in response to intermittent stimulation is complex. In order to study the loss processes operative at the most peripheral level, CM sensitivity at the round window was monitored in a series of acute experiments on 150 cat ears as they were exposed to intermittent or continuous 5.0-kHz pure-tone stimulation. Stimuli were delivered at a SPL either 10 or 30 dB above that intensity necessary to produce a maximum CM output. Stimuli were on a 20% duty cycle with on-times varying from 10 msec to 2 min. Recovery processes taking place between stimuli were also measured. At all but the shortest on-times, loss was bimodally distributed, i.e., ears lost either much more or much less sensitivity than ears exposed to equivalent amounts of continuous stimulation. The shortest on-times, in contrast, tended to produce predominantly large losses. An early recovery process at the level of the CM was explored and found to have the following properties: it proceeded in log-time and the amount of recovery was proportional to the log of the on-time but was unrelated to the amount of residual sensitivity shift. The data were interpreted as showing the possibility that large losses to intermittent stimuli were likely to result when successive stimuli in the intermittent train interrupted the early recovery process before it has run to completion. These data were compared with TTS data from the human ear and parallels noted.