ASA 125th Meeting Ottawa 1993 May

2aPP1. Physiological correlates of the precedence effect: Implications for neural models.

Tom C. T. Yin

Ruth Y. Litovsky

Dept. of Neurophysiol., Univ. of Wisconsin, Madison, WI 53706

The precedence effect is an illusion whereby two similar sounds, delivered from different locations and in quick succession, are perceived as a single auditory event whose apparent location is dominated by the leading sound. Physiological correlates of the precedence effect have been looked for in the responses of single cells in the inferior colliculus (IC) of anesthetized cats. Studies were conducted in both dichotic and free-field conditions by simulating click pairs with variable interclick delays. Almost all cells show a form of echo suppression, whereby the response to a lagging click is suppressed to half-maximal value for interclick delays of 3--150 ms (mode of 29 ms). This result dictates an important role for inhibition in the binaural circuits of the brainstem. It may also provide a resolution for the paradox in which Colburn's models of the medial superior olive (MSO) need no inhibition yet there is strong anatomical evidence for the presence of inhibitory synapses in both MSO and IC. [Work supported by NIH DC00116 and NRSA DC00078.]