Residual effects in monaural temporary threshold shifts to pure tones

Temporary threshold shifts (TTS), of the cochlear action potential in the guinea pig, caused by a high frequency exposure tone could be reduced by a prior exposure at the same frequency but lower intensity. The TTS caused by the initial, low intensity exposure tone was allowed to recover to levels where the thresholds were not significantly different from normal thresholds. Re-exposure at the high intensity now resulted in less TTS being recorded, both at the half-octave point and across the range of frequencies affected by the pure tone, when compared to exposure to the high intensity tone without such priming. This protective effect of prior exposure was not affected by intraperitoneal injections of strychnine, distinguishing it from recent reports of protective mechanisms operative during TTS.