Macaque area V4 neurons translate the attended features of a visual stimulus into behaviorally relevant categories

It is well known that visual attention can enhance processing of restricted regions of space or of individual objects. Recent work has shown that visual attention can also lead to selective processing of individual object features, but clear demonstrations of these feature-specific modulatory effects are still lacking at the level of single neurons. In the present study we cued two macaque monkeys to discriminate either the color or the orientation of a stimulus, while ignoring the other feature of the same stimulus. Sixteen different stimuli varying in color and orientation were presented inside the receptive field (RF) of isolated, dorsal area V4 neurons, while the animal was centrally fixating. We recorded the responses of around 150 cells in the two animals. Attending to a given feature might be expected to sharpen neural selectivity for that feature at the expense of selectivity for the other feature. We assessed this possibility by comparing selectivity for the color and the orientation of the stimuli when either feature was behaviorally relevant. Although ∼40% of the recorded cells were significantly modulated by feature-selective attention, no consistent changes in tuning were found across the cell population, in agreement with previous studies of V4. However, for about one third of the cells, while activity in an early phase post-stimulus onset mainly encoded the features of the RF stimulus, regardless of the specific feature to be attended, activity in a later phase developed to encode which of two alternative behavioral responses was required by the relevant feature of the stimulus. Thus, it appears that feature-selective attention can modulate neural activity in area V4 by translating the attended feature of a visual object into a task-relevant category, i.e., by explicitly representing only the information that is relevant to guide behavior