Delayed Response Following Cochlear Microphonics

-Its Characteristics and Analysis-

Abstract

Cochlear microphonics (CM) and delayed response following CM (DRCM) were investigated in 10 guinea pigs. The acoustic stimuli used were 1 kHz and 4 kHz tone pips. DRCM could be detected in all animals with a threshold less than 35 dB pe SPL in cochlear action potential (AP), but decreased or became undetectable at AP thresholds over 40 dB pe SPL. The input-output curves of DRCM revealed typical nonlinear properties and showed the saturation phenomenon at fairly low sound intensity around 60 dB pe SPL, compared to the sound level at which CM is saturated. Thus, CM and DRCM could be separated by a modification of Probst's method, taking into account their different input-output functions. DRCM differed from CM by being independent of the frequency of acoustic stimulation, although it was dependent on the phase. DRCM seemed to contain relatively low frequency ranges, 0.5 to 2.0 kHz. Therefore, DRCM evoked by 4 kHz tone pips could be separated easily from CM by high-cut filtering. The waveform of DRCM, separated by a modification of Probst's method, was quite similar to that separated by high-cut filtering. Thus, DRCM is thought to be a different evoked potential from CM.