SPATIAL ATTENTION EFFECTS IN MACAQUE AREA V4

Focal visual attention typically produces enhanced perceptual processi ng at the psychological level and relatively stronger neural responses at the physiological level. A longstanding mechanistic question is wh ether these attentional effects pertain specifically to the attended ( target) object or to the region of space it occupies, We show here tha t attentional response enhancement in macaque area V4 extends to behav iorally irrelevant objects in the vicinity of the target object, indic ating that focal attention has a strong spatial component at the physi ological level, In addition, we find that spatial attention effects ty pically show a striking directional asymmetry. The direction of the as ymmetry varies between cells, so that some cells respond best when att ention is directed to the left of the stimulus, some when attention is directed to the right, etc, Thus, attention involves not only enhance d responses to behavioral targets but also a complex modulation of res ponses to other stimuli in the surrounding visual space.