On-line versus off-line control of rapid aiming movements.

Recent studies have shown the importance of visual feedback during the rapid initial phase of aiming movements for the control of direction (e.g., Bard, Paillard, Fleury, Hay, & Larue, 1990; Blouin, Teasdale, Bard, & Fleury, in press; Teasdale, Blouin, Bard, & Fleury, 1991). In most of these studies, visual feedback conditions were presented in blocked sessions. Consequently, higher-order processes (e.g., feedforward and/or learning processes), along with on-line processing of visual feedback, might have contributed to the better accuracy found when subjects had visual feedback of only the initial portion of the movements (compared with movements without visual feedback). To test this possibility, we studied subjects' performance of rapid arm movements under different types of presentation (random, precued, and blocked) of the visual feedback conditions of the trajectory (no vision, initial portion only, and vision of the entire trajectory). Directional errors were larger in the no-vision condition than in both conditions with visual feedback. There were no differences among the presentation conditions, suggesting that on-line processing of visual information contributed to the control of the arm movements.