Distribution of programming in a rapid aimed sequential movement

Studies indicate that rapid sequential movements are preprogrammed and that preprogramming increases with complexity, but more complex sequences that require on-line programming have been seldom been studied. The purpose of this investigation was to determine whether on-line programming occurs in a 7-target sequence in which there is a unique target constraint and if so, to determine how different task constraints affect the distribution of additional programming. Subjects contacted seven targets with a hand-held stylus as quickly as possible while maintaining a 90% hit rate. Initiation-band execution-timing patterns and movement kinematics were measured to determine when the additional programming took place. Results indicated that additional programming occurred before initiation and during movement to the first target when the constraint required more spatial accuracy (small target). A different type of unique target (a triple hit of one target) caused the additional programming to occur on-line one or two segments before its execution. Different positions of the unique target also affected timing patterns. Results were discussed in terms of: (1) capacity of processing; (2) control of movement variance; and (3) mean velocity as a programmed parameter in sequential aiming movements.