Unconscious and out of control: Subliminal priming is insensitive to observer expectations

The rapid-chase theory does not extend to movement execution

It is assumed that the processing of a prime followed by a mask occurs sequentially in a feedforward manner when the three (initiation, takeover, and independence) criteria outlined by the rapid-chase theory are met. The purpose of the current study was to determine if the processing of the prime and mask fit the predictions of the rapid-chase theory when the prime and mask are presented during an ongoing movement. In two experiments, participants made rapid pointing movements to a target indicated by the mask. In Experiment 1, the prime was presented at movement onset and the prime-mask stimulus onset asynchrony (SOA) was manipulated. In Experiment 2, the prime-mask SOA was constant but the delay between movement and prime onset was manipulated. Although the results support the initiation and takeover criteria, the data did not support the independence criterion. Consequently, the rapid-chase theory does not appear to extend to movement execution.

Automatic adjustments toward unseen visual targets during grasping movements

We investigated whether control of hand movements can be driven by visual information that is not consciously perceived. Subjects performed reach-to-grasp movements toward 2D virtual objects that were projected onto a rigid surface. On perturbed trials, the target object was briefly presented at a different orientation (±20° rotation) or different size (±20 % scaling) during movement. The perturbed objects were presented for 33 ms, followed by a 200-ms mask and reappearance of the original target object. Subjects perceived only the mask and were not aware of the preceding perturbed stimuli. Unperturbed trials were identical except that there was no change in the target object before the mask. Despite being unaware of the brief perturbed stimuli, subjects showed corrective adjustments to their movements: rotation of the grip axis in response to orientation perturbations, and scaling of grip aperture in response to size perturbations. Responses were detectable 250-300 ms after the perturbation onset and began to reduce 250-300 ms after the reappearance of the original target. Our results demonstrate that the visuomotor system can utilize visual information for control of grasping even when this information is not available for conscious perception. We suggest that this dissociation is due to different temporal resolution of visual processing mechanisms underlying conscious perception and control of actions.