The problem of reversals in assessing implicit sequence learning with serial reaction time tasks.

We report two experiments in which implicit learning is demonstrated within a short session of practice, in the absence of explicit knowledge of what is learned. In Experiment 1, we replicate the experiments by Curran (Psychol Res 60:24-41, 1997a; J Cogn Neurosci 9(4):522-533, 1997b) and highlight the importance of avoiding a random sequence as comparison to the training sequence, due to the higher proportion of reversal trials included in the random one, which leads to an artifactual measure of learning. In Experiment 2 we present a procedure in which two structurally analogous sequences are used both as training and control sequences, thus controlling for any factor different from learning. The results show that implicit learning is obtained within a short session of practice, and in the absence of any explicit knowledge as assessed through a subsequent generation task. We surmise that this procedure might be especially useful in areas in which short procedures are needed, such as when special populations are tested (e.g., patients, children or elderly people) or when the neural bases of implicit learning are being investigated through neurophysiological measures.