Phenomenal causality: impressions of pulling in the visual perception of objects in motion

Subjects observed computer-generated images of the five opaque rectangles arranged in a vertical column and separated by small gaps. In order from top to bottom, the rectangles began to move horizontally at intervals of a fraction of a second, at constant and identical speeds. Subjects reported a strong impression that the top object was pulling the others, despite the fact that the objects never came into contact or approached each other, moved in different planes, and had no visible connection. The impression was not much affected by speed, direction of motion, or length of delay between successive objects beginning to move. The effect was attenuated if there was prior motion in the opposite direction, if each object in turn rapidly decelerated to standstill, and if all objects began to move simultaneously. It is unlikely that this impression could be mediated by an innate visual mechanism, and it may reflect perceptual learning.