Stimulus-specific competitive selection in macaque extrastriate visual area V4.

Macaque visual area V4 has been implicated in the selective processing of stimuli. Prior studies of selection in area V4 have used spatially separate stimuli, thus confounding selection of retinotopic location with selection of the stimulus at that location. We asked whether V4 neurons can selectively respond to one of two differently colored stimuli even when they are spatially superimposed. We find that delaying one of the two stimuli leads to selective processing of the delayed stimulus by area V4 neurons. This selective processing persists when the stimuli move together across the visual field, thereby successively activating different populations of neurons. We also find that this effect is not a spatially global form of feature-based selection. We conclude that selective processing in area V4 is neither exclusively spatial nor feature-based and may thus be surface- or object-based.