DIRECTIONAL CONTROL OF RAPID ARM MOVEMENTS - THE ROLE OF THE KINETIC VISUAL FEEDBACK-SYSTEM

Vision has long been considered as a single feedback system providing information about the static and the dynamic features of motor behavio rs and of the environment where they take place. However, recent model s for oculomanual movements have included multichanneling of visual cu es (Goodale & Milner, 1992; Jeannerod, 1981; 1984; Paillard, 1980, 198 2). According to Paillard's model, a kinetic system, mostly sensitive to dynamic cues, provides directional information of the movement in t he rapid distance-covering phase, and a static system, highly sensitiv e to position cues, provides positional signal errors. The present exp eriment gives kinematic evidence for the significant contribution of v ision during the initial phase of rapid pointing movements when this p hase is under the control of the kinetic channel. Movements having dir ectional requirements were more accurate (directional precision) when vision of the initial portion of the trajectory was available. Times-t o-peak acceleration and velocity were all shorter and their respective amplitudes were generally higher when vision was available for the fi rst third of the trajectory than when it was not. Further, vision of t he entire trajectory did not yield better precision then when vision w as available for the initial phase of the movements only. Overall, the data support the existence of two corrective visual feedback systems.