Hemispheric asymmetries: Attention to visual and auditory primitives

A computational theory of hemispheric asymmetries in perception (double fil tering by frequency) is described. Its central tenet is that the cerebral h emispheres first perform symmetric filtering of visual and auditory informa tion. Functional hemispheric asymmetry arises from a second filtering 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 wa y, the hemispheric difference becomes one of relative rather than absolute information. Behavioral deficits due to unilateral lesions in neurological patients and neuroimaging and electrophysical measures in normal subjects i mplicate posterior cortex in these hemispheric differences.