Temporal dynamics of early perceptual processing.

Recordings of electrical and magnetic brain responses to sensory stimulation provide high-resolution measures of the time course of early perceptual processing. Spatio-temporal analyses of brain activity patterns during the first 200 ms after stimulus presentation have characterized the timing of attentional selection processes and different stages of feature encoding and pattern analyses. Recent studies that incorporate blood flow neuroimaging techniques provide support for mechanisms of early selection of attended visual inputs in extrastriate cortical pathways. The spatial tuning properties of early auditory selection have also been delineated. Electrical and magnetic responses that index the encoding of higher-order pattern information have been identified in both visual and auditory modalities and localized to specific cortical areas.