The golf-ball illusion: evidence for top-down processing in weight perception.

Theories of weight illusions have traditionally emphasised either the primary contribution of low-level sensory cues or the role of expectation based on knowledge and past experience. Current models of weight illusions lean quite strongly towards sensory-based interpretations. The current experiment raises a problem for such approaches by generating a weight illusion that is difficult to explain other than by the participants' knowledge. Golfers (who expect a weight difference between ball types) reliably judged practice golf balls to weigh more than real golf balls of the same weight. In contrast, non-golfers (who expect no weight difference between ball types) judged practice and real balls of equal weigh to weight the same. Furthermore, within the group of golfers, those who expected the weights of the two ball types to be the most discrepant prior to lifting tended to report the strongest illusions subsequent to lifting. Because there is no low-level sensory cue between ball types that on its own would signal a weight difference, the current finding suggests that there is a top-down component to weight perception that is based on experience with specific objects.