Action and Awareness in Pointing Tasks

Subjects' awareness of motor corrections was investigated in a double-step pointing task. An unpredictable lateral target displacement of 10 cm, either left or right, during an ongoing reaching movement led to corrections of the trajectory. Subjects were required either to follow the target (pointing) or move in the opposite direction (anti-pointing). The target jump elicited rapid corrections to the movement in the direction of the target shift. These corrections were in some sense involuntary as they sometimes occurred in anti-point trials, when subjects were instructed to correct in the opposite direction to the target jump. The instructed correction away from the target in anti-point trials occurred later than the correction towards the target in standard pointing. Subjects were also asked to report their awareness of the motor correction they had just made by immediately reproducing each movement. In normal pointing, subjects showed reduced and delayed awareness, suggesting that the corrections were at least partly automatic. Anti-pointing corrections did not show this dissociation between performance and awareness. We suggest that anti-point corrections, but not standard pointing corrections, involve an additional supervisory system. This system is characterised by its slow operation and its access to conscious awareness.