Emergence of spontaneous anticipatory hand movements in a probabilistic environment

In this article, we present a novel experimental approach to the study ofanticipation in probabilistic cuing. We implemented a modified spatial cuingtask in which participants made an anticipatory hand movement toward one of twoprobabilistic targets while the (x,y)-computer mouse coordinates of their hand movements weresampled. This approach allowed us to tap into anticipatory processes as theyoccurred, rather than just measuring their behavioral outcome through reactiontime to the target. In different conditions, we varied the participants’ degreeof certainty of the upcoming target position with probabilistic pre-cues. Wefound that participants initiated spontaneous anticipatory hand movements in allconditions, even when they had no information on the position of the upcomingtarget. However, participants’ hand position immediately before the target wasaffected by the degree of certainty concerning the target’s position. Thismodulation of anticipatory hand movements emerged rapidly in most participantsas they encountered a constant probabilistic relation between a cue and anupcoming target position over the course of the experiment. Finally, we foundindividual differences in the way anticipatory behavior was modulated with anuncertain/neutral cue. Implications of these findings for probabilistic spatialcuing are discussed.