Degree of certainty modulates anticipatory processes in real time.

In the present study, we investigated how degree of certainty modulates anticipatory processes using a modified spatial cuing task in which participants made an anticipatory hand movement with the computer mouse toward one of two probabilistic targets. A cue provided information of the location of the upcoming target with 100% validity (certain condition), 75% validity (semicertain condition) or gave no information of the location (uncertain condition). We found that the degree of certainty associated with the probabilistic precue on the upcoming target location affected the spatiotemporal characteristics of the anticipatory hand movements in a systematic way. In the case of semicertainty, we found evidence that the anticipatory processes were modulated in a way consistent with a model of graded probability matching biased toward certainty. In the case of uncertainty regarding two equally likely locations, we observed large between- and within-subject variability in the patterns of anticipatory hand movements, suggesting that individual differences in the strategies employed may become relevant when the likelihoods of response options are equal.