Perception - action dissociations depend on factors that affect multisensory processing

Behavioral perception-action dissociations are widely used to test models of high-level vision, but debates concerning their interpretation have underestimated the role of multisensory mechanisms in such tests. Sensorimotor tasks engage multisensory processing in fundamentally different ways in comparison to perceptual tasks, and these differences can modulate the effects of illusion in specific ways in accord with the features of the experimental task. To test this idea, we compared perception and action using a well-understood size-contrast effect, the Uznadze illusion, and manipulated both unimodal and crossmodal stimulation as well as 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.