Perceptual decisions about object shape bias visuomotor coordination during rapid reaching and interception

Visual processing in parietal areas of the dorsal stream facilitates sensorimotor transformations for rapid movement. This action-related visual processing is hypothesized to play a distinct functional role from the perception-related processing in the ventral stream. However, it is unclear how the two streams interact when perceptual identification is a prerequisite to executing an accurate movement. In the current study, we investigated how perceptual decision-making involving the ventral stream influences eye and arm movement strategies. Participants (N = 26) moved a robotic manipulandum using right whole-arm movements to rapidly reach a stationary object or intercept a moving object on a virtual display. On some blocks of trials, participants needed to identify the shape of the object (circle or ellipse) as a cue to either hit the object (circle) or move to a pre-defined location away from the object (ellipse). We found that interception movements were initiated sooner and performed less accurately than reaches, a difference that increased in trials when perceptual decisions about object shape were made. Faster hand reaction times were correlated with a deliberate strategy to adjust the movement post-initiation - this strategy was more prominent during interception, when there is a greater perceived urgency to act. Saccadic reaction times were faster and initial smooth pursuit lags and gains greater during decisions, suggesting an interference between how eye movements are used for perception and for guiding limb movements. Together, our findings suggest that the extent to which ventral stream information is incorporated in into visuomotor planning depends on imposed (or perceived) task demands.