Résumé
Here we show that a perceptual size-weight illusion can occur even when participants show
no expectation that the masses of the two objects ought to be different, calling into question
the validity of expectation-mismatch accounts of the illusion. In the critical experimental group,
participants lifted a large and small object with the same mass but different colors. Unlike a
group who lifted objects with the same colors, participants in the different color group showed
equivalent grasping dynamics for the two objects on the first lifting attempts, indicating that
they did not hold incorrect expectations about object mass. Both groups showed an equally
robust perceptual SWI over 15 repeated lifts. The results from this study are consistent with a
density-based account of the perceptual SWI according to which participants judge the
heaviness of an object based on its density relative to the norm for other members of its class.
