Hemispheric Asymmetries

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Abstract
A computational theory of hemispheric asymmetries in perception (double filtering by frequency) is described. Its central tenet is that the cerebral hemispheres first perform symmetric filtering of visual and auditory information. Functional hemispheric asymmetry arises from a second filtering stage (containing filters skewed in different directions in the two hemispheres). The first stage selects a range of task-relevant spatial or auditory frequencies from the absolute values. This range is passed to the asymmetric filters. In this way, the hemispheric difference becomes one of relative rather than absolute information. Behavioral deficits due to unilateral lesions in neurological patients and neuroimaging and electrophysiological measures in normal subjects implicate posterior cortex in these hemispheric differences.