An invisible stimulus influences pointing trajectories even when presented during movement

Abstract

In the masked priming paradigm, a small visual (prime) stimulus is briefly presented and quickly followed by a larger visible (mask) stimulus, which indicates the target location and prevents the prime from reaching conscious awareness. Previous studies in which participants were required to complete a pointing response in accordance with the identity of the mask have shown that the prime, when presented at movement onset, initially results in deviations in the direction indicated by the prime. The purpose of the current experiment was to determine whether the prime is able to influence movement when it is presented following various delays relative to movement onset, as depending on movement velocity, the prime may be unable to influence the movement to the same extent when presented later in the trajectory. Twelve participants initiated 540 rapid reaches to a center target. The prime was presented 17, 33, or 50 ms after movement onset followed 50 ms later by the mask. On 66% of the trials, participants landed on the center target within 400-600 ms in response to a neutral prime and mask. In the remaining trials, a neutral, left or right-pointing prime arrow preceded a left or right-pointing mask arrow requiring participants to modify their movements to the respective target. Regardless of prime onset delay, movement deviations first occurred in the direction indicated by the prime. Consequently, the prime was still able to influence the movement despite the prime appearing later during the pointing trajectory.

Acknowledgments: OGS, NSERC