Perceived surface shape not features determines correspondence strength in apparent motion.

Previous psychophysical studies have revealed that shape similarity can affect apparent motion correspondence. Such results however, do not specify the level of representation, at which shape similarity is defined. We sought to understand this question by using a 2 x 2 competitive apparent motion paradigm. We manipulated the binocular disparity of the motion stimuli (tokens) relative to adjacent squares to selectively change the internal surface representation of the tokens while keeping early filtered representation intact. When two sets of differently oriented tokens (45 degrees,-45 degrees bars) were used, there was a preference for seeing motion between tokens having the same orientation. However, such a motion bias was reduced when tokens became part of a large surface square seen either as amodally occluded in the background or as a transparent surface modally completed in front. Since shape differences at the early filtering level remain essentially intact (i.e. + 45 degrees vs -45 degrees) our findings support the surface level hypothesis. Perceived surface shape rather than shape defined by early filters largely determines motion correspondence.