Effects of an acute acoustic trauma on the representation of a voice onset time continuum in cat primary auditory cortex

Here we show that hearing loss associated with an impairment of speech recognition causes a decrease in neural temporal resolution. In order to assess central auditory system changes in temporal resolution, we investigated the effect of an acute hearing loss on the representation of a voice onset time (VOT) and gap-duration continuum in primary auditory cortex (AI) of the ketamine-anesthetized cat. Multiple single-unit activity related to the presentation of a /ba/-/pa/ continuum - in which VOT was varied in 5-ms step from 0 to 70 ms - was recorded from the same sites before and after an acoustic trauma using two 8-electrode arrays. We also obtained data for gaps, of duration equal to the VOT, embedded in noise 5 ms after the onset. We specifically analyzed the maximum firing rate (FRmax), related to the presentation of the vowel or trailing noise burst, as a function of VOT and gap duration. The changes in FRmax for /ba/-/pa/ continuum as a function of VOT match the psychometric function for categorical perception of /ba/-/pa/ modeled by a sigmoid function. An acoustic trauma made the sigmoid fitting functions shallower, and shifted them toward higher values of VOT. The less steep fitting function may be a neural correlate of an impaired psychoacoustic temporal resolution, because the ambiguity between /ba/ and /pa/ should consequently be increased. The present study is the first one in showing an impairment of the temporal resolution of neurons in AI caused by an acute acoustic trauma. (C) 2004 Elsevier B.V. All rights reserved.