Motion and color generate coactivation at postgrouping identification stages

Response times (RTs) were measured in a postgrouping visual identification task. Shapes composed of multiple elements were distinguished by color, motion, orientation, and spatial frequency alone or in pairwise conjunctions. The largest amount of redundancy gain, requiring coactivation as revealed by a race model analysis, was obtained with color-motion conjunctions. In contrast, RTs for a pregrouping detection task using the same target shape as in the identification task, distinguished by color, motion, or a conjunction of these features, showed no evidence for coactivation. The results provide psychophysical evidence for coactivation of color and motion signals in cortical regions specialized for grouping and object identification, as opposed to separate processing of these features in cortical area V1, believed to limit performance in visual search and pregrouping detection.