ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

2pPP9. Contralateral stimulation and the masking overshoot effect.

Christopher W. Turner

Rebecca Waite

Karolyn Cummings

Melanie Rosen

Syracuse Univ., Program in Commun. Sci. and Disord. and Inst. for Sensory Res., 805 South Crouse Ave., Syracuse, NY 13244

Overshoot is the increase in masked threshold for a short signal presented at the onset of a masker compared to the threshold for a signal presented in the temporal center of the masker. One hypothesis to explain this effect is the slow onset time for masker-stimulated ipsilateral efferent activity to influence the response to the masked signal. Recent physiological experiments have shown that noise presented to the contralateral ear, which provides an increment in efferent activity, can increase the neural detectability of short tones masked by noise [Kawase et al., J. Neurophys. 70, 2533--2549 (1993)]. The present behavioral experiment took advantage of these findings and measured the amount of overshoot under conditions where a brief contralateral noise was presented prior to the masker onset, in an attempt to ``prime'' the efferent system prior to the masker onset. All measurements were conducted using insert earphones, which provide approximately 80 dB of interaural attenuation. The preceding contralateral noise reduced or eliminated the overshoot across a wide range of masker levels. Possible mechanisms for the overshoot effect will be discussed. [Work supported by NIDCD.]