Dividing attention between color and shape revisited: redundant targets coactivate only when parts of the same perceptual object.

When a single perceptual object provides two different reasons for a particular decision (by containing two qualitatively different targets), detailed analyses of the response-time distributions have shown that the two different reasons are jointly responsible for the final decision. The question is whether this coactivation occurs because the two targets contained by the object were from separate dimensions (e.g., color and shape) or were parts of the same perceptual object. Early work argued in favor of dimensions, implying that the types of information being processed is critical, as opposed to their sources; more recent work has argued in favor of objects. Experiment 1 in the present paper corrected for a potential bias in the design of some recent studies and found additional evidence in favor of objects. Two additional experiments directly manipulated whether redundant targets would be perceived as parts of one or two perceptual objects (while holding all else constant) and produced the strongest evidence to date that coactivation requires that the redundant targets be parts of one object. This reverses the original conclusion and suggests that the sources of information are critical, as opposed to the types. Two specific versions of the object-based model are discussed.