Peripheral constraint versus on-line programming in rapid aimed sequentialmovements

The purpose of this investigation was to examine how the programming and co ntrol of a rapid aiming sequence shifts with increased complexity. One obje ctive was to determine if a preprogramming/peripheral constraint explanatio n is adequate to characterize control of an increasingly complex rapid aimi ng sequence, and if not, at what point on-line programming better accounts for the data. A second objective was to examine when on-line programming oc curs. Three experiments were conducted in which complexity was manipulated by increasing the number of targets from I to 11. Initiation- and execution -timing patterns, probe reaction time (RT), and movement kinematics were me asured. Results supported the peripheral constraint/pre-programming explana tion for sequences up to 7 targets if they were executed in a blocked fashi on. For sequences executed in a random fashion (one length followed by a di fferent length), preprogramming did not increase with complexity, and on-li ne programming occurred without time cost. Across all sequences there was e vidence that the later targets created a peripheral constraint on movements to previous targets. We suggest that programming is influenced by two fact ors: the overall spatial trajectory, which is consistent with Sidaway's sub tended angle (SA) hypothesis (1991), and average velocity, with the latter established based on the number of targets in the sequence. As the number o f targets increases, average velocity decreases, which controls variability of error in the extent of each movement segment. Overall the data support a continuous model of processing, one in which programming and execution co -occur, and can do so without time cost. (C) 2001 Elsevier Science B.V. All rights reserved.