Independence of perceptual and sensorimotor predictions in the size-weightillusion

The smaller of two equally weighted objects is judged to be heavier when li fted. Here we disproved a leading hypothesis that this size-weight illusion is caused by a mismatch between predicted and actual sensory feedback. We showed that when subjects repeatedly lifted equally heavy large and small o bjects in alternation, they learned to scale their fingertip forces precise ly for the true object weights and thus exhibited accurate sensorimotor pre diction. The size-weight. illusion nevertheless persisted, suggesting that the illusion can be caused by high-level cognitive and perceptual factors a nd indicating that the sensorimotor system can operate independently of the cognitive/perceptual system.