INTERACTION OF COGNITIVE AND SENSORIMOTOR MAPS OF VISUAL SPACE

Studies of saccadic suppression and induced motion have suggested sepa rate representations of visual space for perception and visually guide d behavior. Because these methods required stimulus motion, subjects m ight have confounded motion and position. We separated cognitive and s ensorimotor maps without motion of target, background, or eye, with an ''induced Roelofs effect'': a target inside an off-center frame appea rs biased opposite the direction of the frame. A frame displayed to th e left of a subject's center line, for example, will make a target ins ide the frame appear farther to the right than its actual position. Th e effect always influences perception, but in half of our subjects it did not influence pointing. Cognitive and sensorimotor maps interacted when the motor response was delayed; all subjects now showed a Roelof s effect for pointing, suggesting that the motor system was being fed from the biased cognitive map. A second experiment showed similar resu lts when subjects made an open-ended cognitive response instead of a f ive-alternative forced choice. Experiment 3 showed that the results we re not due to shifts in subjects' perception of the felt straight-ahea d position. In Experiment 4, subjects pointed to the target and judged its location on the same trial. Both measures showed a Roelofs effect , indicating that each trial was treated as a single event and that th e cognitive representation was accessed to localize this event in both response modes.