MOVEMENT VARIABILITY AS A FUNCTION OF ACCURACY DEMAND IN PROGRAMMED SERIAL AIMING RESPONSES

Recent research suggests that when a response comprises a series of ta rgets, programming time may be a function of the target within the res ponse that imposes the greatest accuracy demand (Sidaway, Schoenfelder -Zohdi, & Moore, 1990). If this accuracy demand affects the programmin g process, one might expect to find evidence of this demand in the con sequent response execution. Of primary interest in the present researc h was the dispersion of target contacts on the first target, in a sequ ence of two targets, when the accuracy demand of the second target was changed. Two experiments are reported that required subjects to rapid ly strike two targets in series within a simple reaction time paradigm . The size of the first target was kept constant, whereas the size of the second target was varied and was always smaller than the first. Ex periment 1 did not require any direction change in the responses, but in Experiment 2, subjects had to make a 90 degrees direction change in the responses. In both experiments, the dispersion and location of st ylus contacts on the first target was a function of the size of the se cond target. When the size of the second target was reduced, the dispe rsion of the first target contacts decreased and the mean location of those contacts moved closer to the second target. Reaction time increa sed as the size of the second target decreased. These findings suggest that the maximal accuracy demand of a serial response influences both the programming and execution phases of the response.