The neural basis of biased competition in human visual cortex

A typical scene contains many different objects that compete for neural rep resentation due to the limited processing capacity of the visual system. At the neural level, competition among multiple stimuli is evidenced by the m utual suppression of their visually evoked responses and occurs most strong ly at the level of the receptive field. The competition among multiple obje cts can be biased by both bottom-up sensory-driven mechanisms and top-down influences, such as selective attention. Functional brain imaging studies r eveal that biasing signals due to selective attention can modulate neural a ctivity in visual cortex not only in the presence, but also in the absence of visual stimulation. Although the competition among stimuli for represent ation is ultimately resolved within visual cortex, the source of top-down b iasing signals likely derives from a distributed network of areas in fronta l and parietal cortex. Attention-related activity in frontal and parietal a reas does not reflect attentional modulation of visually evoked responses, but rather the attentional operations themselves. Published by Elsevier Sci ence Ltd.