NEURAL BASIS FOR PHENOMENA SURROUNDING PRECEDENCE EFFECT

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In most natural environments, wavefronts from a single source will reach a listener through both direct and reflected paths. The direct path is the shortest distance between the source and the listener. while the reflected paths are longer and yield wavefronts that arrive at the listener from multiple directions. Despite the multiplicity of information, the listener perceives a spatially distinct sound localized at the position of the source. Because the location of the wavefront that arrives first dominates the spatial percept, the phenomenon is called the "law of the first wavefront" or the "precedence effect". Because of its importance for understanding binaural information processing in general, and the localization of sounds in reverberant environments in particular, the conditions under which the "precedence- effect" and related events occur have been extensively studied. Despite the wealth of behavioral data, there appear to be no published electrophysiological studies that explain the neural basis of the phenomena surrounding the "precedence effect". Our preliminary studies indicate that neurons in the inferior colliculus (IC) of the "awake" rabbit can show responses consistent with phenomena surrounding the "precedence effect". We propose a series of investigations predicated on our preliminary observations that capitalize on the collaborative efforts of neurophysiologists and psychoacousticians. Our goal is to elucidate the neural mechanisms and pathways that underlie several important psychoacoustic phenomena concerning the processing of successive acoustic stimuli, including the "precedence effect". To that end, single-unit recording will be made in the IC of the "awake" rabbit. We will examine the effects on these responses of chemically inactivating the dorsal nucleus of the lateral lemniscus which we hypothesize is a major source of inhibitory input to the IC.