The Influence of Premovement Visual Information on Manual Aiming

Abstract

Three experiments were conducted to determine whether a visual representation of the movement environment, useful for movement control, exists after visual occlusion. In Experiment 1 subjects moved a stylus to small targets in five different visual conditions. As in other studies (e.g. Elliott and Allard, 1985), subjects moved to the targets in a condition involving full visual information (lights on) and a condition in which the lights were extinguished upon movement initiation (lights off). Subjects also pointed to the targets under conditions in which the lights went off 2, 5 and 10 sec prior to movement initiation. While typical lights-on-lights-off differences in accuracy were obtained in this experiment (Keele and Posner, 1968), the more striking finding was the influence of the pointing delay on movement accuracy. Specifically, subjects exhibited a twofold increase in pointing error after only 2 sec of visual occlusion prior to movement initiation. In Experiment 2, we were able to replicate our 2-sec pointing delay effect with a between-subjects design, providing evidence that the results in Experiment 1 were not due to asymmetrical transfer effects. In a third experiment, the delay effect was reduced by making the target position visible in all lights-off situations. Together, the findings provide evidence for the existence of a brief (< 2 sec) visual representation of the environment useful in the control of aiming movements.