Visual attention enhances perception of visual information important for goal-directed behavior. Numerous electrophysiological and neuroimaging studies have shown that attention to spatial location leads to enhancement of neural activity at the attended location. However, fewer studies have focussed on feature-based attention (e.g. attention to color or shape). We have recently shown using optical imaging in awake behaving monkeys that area V4, a cortical area known to be strongly modulated by attention, contains modular organization for color and orientation preference.  In this study, we examine the effect of spatial attention and feature attention on the activation of these feature-specific domains. We hypothesize two possible modes of attentional modulation—either modulation of domain response magnitude or of domain response correlation. By conducting intrinsic signal optical imaging of V4 in macaque monkeys trained to perform spatial or featurea attention tasks, we find that spatial attention is mediated via response enhancement, while feature attention is mediated via changes in response correlation. We therefore propose that spatial and feature attention are implemented via orthogonal changes in cortical network circuitry. These findings have implications for bottom up vs top down neural processes and our understanding of conditions involving specific types of attentional dysfunction.