Perception and action in unimodal and crossmodal illusions: Towards a resolution of a long-standing debate in behavioural cognitive neuroscience

Behavioral perception-action dissociations are widely used to test models of high-level vision1,2, but debates concerning their interpretation have neglected a key issue. Environmental determinants of behavior are fundamentally multisensory3, and sensorimotor tasks can engage multisensory processing in fundamentally different ways in comparison to perceptual tasks. To test this idea, we compared perception and action with a well-understood size-contrast illusion, manipulating both unimodal and crossmodal stimulation as well conditions that are known to favor or hinder multisensory integration. Results demonstrate that varying such conditions can cause a visual task to be affected by the illusion, or remain fully unaffected, whereas a visuomotor task can be affected by the illusion, remain immune from the illusion, or, unexpectedly, even show a robust reverse effect. Thus, similar or dissociable effects on perception and action can be observed depending on factors that are known to affect multisensory processing. These findings provide a novel perspective on a long standing debate in behavioral cognitive neuroscience.