Attention modulates contextual influences in the primary visual cortex of alert monkeys

The response properties of cells in the primary visual cortex (V1) were mea sured while the animals directed their attention either to the position of the neuron's receptive field (RF), to a position away from the RF (focal at tention), or to four locations in the visual field (distributed attention). Over the population, varying attentional state had no significant effect o n the response to an isolated stimulus within the RF but had a large influe nce on the facilitatory effects of contextual lines. We propose that the at tentional modulation of contextual effects represents a gating of long rang e horizontal connections within area V1 by feedback connections to V1 and t hat this gating provides a mechanism for shaping responses under attention to stimulus configuration.