Abstract
Single-unit recording studies in the macaque have carefully documented
the modulatory effects of attention on the response properties of
visual cortical neurons. Attention produces qualitatively different
effects on firing rate, depending on whether a stimulus appears alone
or accompanied by distracters. Studies of contrast gain control in
anesthetized mammals have found parallel patterns of results when
the luminance contrast of a stimulus increases. This finding suggests
that attention has co-opted the circuits that mediate contrast gain
control and that it operates by increasing the effective contrast
of the attended stimulus. Consistent with this idea, microstimulation
of the frontal eye fields, one of several areas that control the
allocation of spatial attention, induces spatially local increases
in sensitivity both at the behavioral level and among neurons in
area V4, where endogenously generated attention increases contrast
sensitivity. Studies in the slice have begun to explain how modulatory
signals might cause such increases in sensitivity.
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