When moving from a starting position to a single target, movement time is faster than when you must continue the movement to a second target (i.e., one-target advantage). Research has now shown that processes underlying both the movement integration and constraint hypotheses account for the preparation and control of sequential aiming movements. In the present study, we investigated how these processes are influenced by the sequencing of single and two target movements and prior knowledge of the number of targets. Participants performed aiming movements to one or two targets on a horizontally positioned touch screen. Three different trial sequences were administered. All movements were performed as an extension from the center of the participant outward. One and two target responses were organised as blocked (i.e., 1-1-1-2-2-2), alternating (i.e., 1-2-1-2-1-2), and random (i.e., 1,1,2,1,2,2) trial sequences. The one-target advantage emerged during the blocked and alternate conditions but not the random condition. This finding suggests that the emergence of the one-target advantage is contingent on prior knowledge of the number of targets. This finding complements previous research that has shown that reaction time increases as a function of the number of movement segments only when the number of segments is known in advance of stimulus onset. Results are discussed as they pertain to the movement constraint and movement integration hypotheses.
Keywords: one-target advantage, reaction time, movement constraint hypothesis, movement integration hypothesis