[Effects of acoustic overstimulation of 2F1-F2 distortion product in cochlear microphonics]

The cochlear microphonics (CM) response to two-tone stimuli was measured before and after exposure to 4 kHz pure tone at 100 dB SPL or 125 dB SPL. The 2f1-f2 distortion products in the CM (CM-DPs) were markedly suppressed by the sound exposure at either intensity, although the loss of CM output at the primary frequencies was limited to 4 dB or less. The suppression of CM-DPs was greater as the intensity of primary tones decreased, especially at primary intensities below 55 dB. These results show that the active transduction process in the cochlea was affected by acoustic overstimulation. This impairment of active transduction was postulated to be an initial process in developing noise induced temporary and/or permanent threshold shift.