Curved Apparent Motion Initiated by a Causal Launch

When objects collide, observers perceive not only the motion but also causal relations, such as which objects caused which others to move. The present study investigated whether such causal interpretations can influence the perceived path of apparent motion. We presented a display of two alternately flashing motion tokens on the ends of a semicircular occluder, and two additional “context objects” placed immediately above the tokens moved upward at each token onset. In such a display the motion token was seen as moving along the curved path behind the occluder, deviating from the default shortest straight path. This finding suggested that observers spontaneously attributed the vertical displacement of the context object to collision by the motion token, which affected the percept of the path of the colliding token. To rule out a potential alternative explanation based on motion priming, a subsequent experiment tested new displays in which the spatial or temporal pattern of context events was altered in ways that preserved or strengthened motion priming, but weakened the causal interpretation. We found that curved apparent motion was observed far more often when it was consistent with a causal launch than when it was not, regardless of priming, suggesting that curved motion is indeed induced by the causal interpretation placed on the collision. In sum, our results suggest that perceived causality is not merely a summary interpretation imposed upon motions already determined by perceptual processes, but rather may make a fundamental contribution to the disambiguation of the underlying sensory signal itself