Neural Correlates of Discriminative Processing in the Human Visual System

Abstract:
Previous studies of visual processing in humans using event-related potentials (ERP) have demonstrated that the modulation of an early component called "N1" (140-200ms) reflects the operation of a discrimination process within the focus of attention. The present study was designed to localize the neuroanatomical sources of this component by means of combined magnetoencephalographic (MEG) and ERP recordings. In two experiments, discrimination processes based on color and movement cues were investigated. Source localization in individual subjects using their anatomical MR scans revealed highly reliable and focused activity in the left and right inferior occipital temporal cortex. Furthermore, electromagnetic source activity for color- and movement-based discriminations arose from similar cortical origins. These findings are consistent with the proposal that the earliest measurable correlates of discriminative operations in the visual system appear as cue-independent neural activity in circumscribed regions of the ventral processing stream.