This project will clarify neural mechanisms important for auditory scene analysis by examining electrophysiological responses in monkey auditory cortex. Scene analysis is a fundamental process whereby speech and other overlapping environmental sounds are perceptually segregated into discrete sources, or merged into unified auditory images. Dysfunction of scene analysis may be a cause of developmental language disorders in many people. Relating these deficits to dysfunction of specific neural events requires an understanding of normal processes best accomplished by intracranial recordings not generally feasible in humans. Monkeys are a superior model because they share many features of sound perception and auditory cortical anatomy with humans. Measures include multiunit activity, evoked potentials, current source density, and frequency-specific electroencephalographic changes. These measures yield stable indices of the synchronized neural activity required for sound encoding, and afford linkage with homologous responses in humans. Substrates of scene analysis will be examined in the framework of a critical appraisal of the dual-stream hypothesis for sound processing, which proposes two discrete auditory cortical pathways that preferentially encode the nature (""""""""what"""""""") and location (""""""""where"""""""") of sounds. Neural representation of three sound attributes critical for scene analysis will be evaluated: 1) common temporal onsets of stimulus components, 2) inharmonicity of stimulus components, and 3) spatial location. The dual-stream hypothesis predicts differential representation of these attributes along the two pathways. Experiments will address the specific aims of this project, which are to test the following hypotheses: (1) Context- dependent activity present at the earliest levels of cortical processing helps shape scene analysis, and (2) Dual cortical pathways differentially represent spatial and non-spatial sound features. This project will enhance understanding of how sound information crucial for perception is processed within auditory cortex. Identifying neural mechanisms involved in scene analysis will clarify normal hearing processes, and serve as a benchmark to evaluate dysfunctional mechanisms associated with abnormal language development. ? ? ?
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