A clockwork orange: compensation opposing momentum in memory for location.

Libet, Gleason, Wright, and Pearl's (1983; Libet, 1985) influential work using a clock-watching task suggests that voluntary actions are initiated in motor cortex prior to the point where the participant claims to have initiated that action. Joordens, van Duijn, and Spalek (2002) showed that a bias exists in this task with respect to the participants' reports of initiation times. Joordens et al. assumed that this bias was primarily due to motion cues that are very much like those used to elicit phenomena such as representational momentum. In the present Experiment 1, it is demonstrated that this bias disappears when a mouse-click response is used in place of a temporal-order judgment. This finding, however, is actually more confusing than clarifying given that the procedural parallels with representational momentum are still present and should be supporting a bias. In the three subsequent experiments the view that a bias is indeed present, but that it is opposed by an opposite-acting compensation process, is proposed and tested. Implications for both representational momentum and for the general use of clock-watching tasks (e.g., Libet et al., 1983) are highlighted.