Sensory biases produce alternation advantage found in sequential saccadic eye movement tasks.

In two-choice reaction time tasks, participants respond faster when the correct decision switches across consecutive trials. This alternation advantage has been interpreted as the guessing strategies of participants. Because the participants expect that the correct decision will switch across consecutive trials, they respond faster when this expectation is confirmed and they respond more slowly when it is disconfirmed. In this study, we evaluated the veracity of this expectancy interpretation. After replicating a long-lasting alternation advantage in saccadic reaction times (Experiment 1), we show that reducing the participants' ability to guess with a challenging mental rotation task does not change the alternation advantage, which suggests that expectancy is not responsible for the effect (Experiment 2). Next, we used prosaccade and antisaccade responses to dissociate between the sensory and motor contributions of the alternation advantage (Experiment 3) and we found that the alternation advantage originates from sensory processing. The implications of these findings are discussed with regard to guessing strategies, sensory processing, and how these findings may relate to inhibition of return.