Occlusion, symmetry, and object-based attention: Reply to Saiki (2000)

J. Saiki (2000) argued that, because the stimuli used by M. Behrmann, R. S. Zemel, and M. C. Meter (1998) were confounded by symmetry, conclusions abo ut whether amodally completed objects can benefit from object-based attenti on are unwarranted. Here, the authors examine J. Saiki's claim further and expand on their view of the mechanisms underlying object-based attention, s uggesting that perceptual organization is the process whereby features from a single object are selectively attended. In light of this, they claim tha t heuristics such as symmetry and collinearity play an important role in th e facilitation of features from a single object. In support of this claim, they present data from a further experiment using displays that exploit com mon fate, another grouping heuristic, and show that, under these conditions , the hallmark of object-based attention, a single-object advantage, is obt ained for the occluded (amodally completed) shapes.