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Activity in the Visual Cortex is Modulated by Top–Down Attention Locked to Reaction Time

California Institute of Technology, University of Zürich, Swiss Federal Institute of Technology, Zürich

Reprint requests should be sent to Farshad Moradi, Computation and Neural Systems Program, California Institute of Technology, Pasadena, CA 91125, M/C 139-74, or via e-mail: farshadm{at}caltech.edu.

We studied the correlation between perception and hemodynamic activity in the visual cortex in a change detection task. Whenever the observer perceived the location of a change, rightly or wrongly, the blood oxygenation level-dependent signal increased in the primary visual cortex and the nearby extrastriate areas above the baseline activity caused by the visual stimulation. This non-sensory-evoked activity was localized and corresponded to the perceived location of the change. When a change was missed, or when observers attended to a different task, the change failed to evoke such a response. The latency of the nonsensory component increased linearly with subjects' reaction time, with a slope of one, and its amplitude was independent of contrast. Control experiments are compatible with the hypothesis that the nonsensory hemodynamic signal is mediated by top-down spatial attention, linked to (but separate from) awareness of the change.

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