COGNITIVE CHANNELS COMPUTING ACTION DISTANCE AND DIRECTION

Visually guided, goal-directed reaching requires encoding action dista nce and direction from attributes of visual landmarks. We identified a cognitive mechanism that seemingly performs visual motor extension be fore action initiation and replicated and extended previous results th at identified a mechanism for visual motor mental rotation. We find th at humans systematically delay action onset while newly planning incre asingly distant arm movements beyond a visual landmark, consistent wit h an internal representation for visual motor extension. Onset times a lso changed systematically during concurrent mental rotation and visua l motor extension computations required to process new directions and distances. Visual motor extension associated with reaching slowed when participants needed to plan action direction within the same time fra me, whereas mental rotation efficiency was unaffected by concurrent ne eds to prepare action distance. In contrast to parallel direction and distance computations needed for direct aiming to a visual target, the planning of new directions and distances likely occurs at distinct ti mes. When considered with previous findings, the current results sugge st the existence of an intermediate component of motor preparation tha t engages a covert mechanism of cognitive motor planning.