PERCEPTUAL UNIT FORMATION IN SIMPLE MOTION PATTERNS

The present study investigated the proximal constraints that determine perceptual unit formation under minimal stimulus conditions. Projecti ons of three moving dots, which could form two possible two-dot config urations, were presented to naive observers.;In a forced-choice situat ion, their task was to report which two-dot configuration was perceive d as a distinct perceptual unit. The results showed that common motion s (arbitrary translations and rigid rotations in the frontoparallel pl ane) have stronger grouping power as compared to different relative mo tions (expansions/contractions, or simultaneous expansions/contraction s and deformations in the frontoparallel plane). It was found that pro ximal changes of distances between elements in two-dot structures redu ce grouping power. Changes of proximal directions, however, did not af fect unit formation in two-dot structures at all. The effect of vector algebraic combinations on grouping power in three-dot strutures was a lso investigated. Evidently, visual vector analysis splits up motion c ombinations into their constituents, and in come cases this contribute s to additive effects.