Selective and interactive neural correlates of visual dimension changes and response changes.

In an event-related fMRI study, we investigated the neural correlates of visual dimension and response changes. We used a compound task, which required target selection by a singleton feature, a unique color or motion direction, before the appropriate motor response, which was determined by target orientation, could be selected. Both types of change elicited distinct patterns of activation, with dimension-change-related activation primarily in posterior visual areas and response-related activation primarily in motor-related areas of the parietal and frontal cortices. Response-change-related activation was delayed by about 1 s relative to dimension-change-related activation, suggesting that the latter is elicited by perceptual processes, whereas the former reflects response-related or post-response processes. Although dimension changes and response changes rely on different processes, they are not independent: response facilitation was observed for combined dimension and response repetitions, this facilitation, however, was disrupted by dimension changes.