Final Report Summary - VISUAL ATTENTION (Revealing the neural mechanisms of attentional selection in the human visual cortex) Imagine you are watching a soccer game, carefully attending to the player on your favorite team to determine which direction he will go. In studies on visual perception, the player is considered an “object”, which has multiple features: direction of motion, the color of his outfit, etc. Can you voluntarily restrict attention to just the player’s direction of motion, the feature that is relevant for your decision, or does your attention unintentionally spread to also enhance the particular shade of orange in his shirt? Major theories of visual attention assume that attending to one feature of a visual object automatically results in selection of the whole object, including task-irrelevant features, but are they correct in assuming that the complete object comprises the basic unit of selection? The overall aim of this research is to reveal the neural mechanisms of selective attention by addressing this issue. We focus on three major research questions: what is the unit of selective attention, how does selective attention affect early visual response properties, and how does selective attention impact perceptual learning? We address these questions using a combination of behavioral, theoretical and neuroimaging techniques, together with novel “decoding” methods to analyze brain activity patterns. Our results indicate that top-down attention is capable of selectively enhancing the processing of a single task-relevant visual feature, without spreading to task-irrelevant features. We furthermore find that the way that attention impacts neural responses depends on the type of attention being deployed. Finally, we show that extensive training on a perceptual task can refine the neural representation of behaviorally relevant information, and that visual attention may play a critical mediating role in revealing these training-based effects. These results provide important new insights into the neural basis of selective attention, with significant implications for theories of visual attention and theories of cortical visual function.