MODULATION OF HUMAN EXTRASTRIATE VISUAL PROCESSING BY SELECTIVE ATTENTION TO COLORS AND WORDS

The present study investigated the effect of visual selective attentio n upon neural processing within functionally specialized regions of th e human extrastriate visual cortex. Field potentials were recorded dir ectly from the inferior surface of the temporal lobes in subjects with epilepsy. The experimental task required subjects to focus attention on words from one of two competing texts. Words were presented individ ually and foveally. Texts were interleaved randomly and were distingui shable on the basis of word colour, Focal held potentials were evoked by words in the posterior part of the fusiform gyrus, Selective attent ion strongly modulated long-latency potentials evoked by words. The at tention effect co-localized with word-related potentials in the poster ior fusiform gyrus, and was independent of stimulus colour. The result s demonstrated that stimuli receive differential processing within spe cialized regions of the extrastriate cortex as a function of attention . The late onset of the attention effect and its co-localization with letter string-related potentials but not with colour-related potential s recorded from nearby regions of the fusiform gyrus suggest that the attention effect is due to top-down influences from downstream regions involved in word processing.