Emergent features, attention, and object perception.

The perceptual processing of arrows and triangles and of their component angles and lines was explored in a number of different tasks. The results suggest that some analysis of shapes into simpler parts occurs preattentively, because these parts can recombine to form illusory conjunctions when attention is divided. The presence of "emergent features," such as closure or arrow junctions, was inferred from predicted correlations in the pattern of performance across tasks and across individual subjects. Thus triangles (for most subjects) and arrows (for some subjects) behave as if they had a perceptual feature that is absent from their parts and that mediates parallel detection in search and easy texture segregation. For some subjects, circles could apparently supply the additional feature (presumably closure) required to form illusory triangles from their component lines, whereas for other subjects circles had no effect. The fact that triangle lines can form illusory conjunctions with another shape makes it unlikely that triangles are perceived holistically and strengthens the interpretation that relies on emergent features.