On-line control of pointing is modified by unseen visual shapes

Shapes that are rendered invisible through backward masking are still able to influence motor responses: this is called masked priming. Yet it is unknown whether this influence is on the control of ongoing action, or whether it merely influences the initiation of an already-programmed action. We modified a masked priming procedure (Schmidt, 2002) such that the critical prime-mask sequence was displayed during the execution of an already-initiated goal-directed pointing movement. Psychophysical tests of prime visibility indicated that the identity of the prime shapes were not accessible to participants for conscious report. Yet detailed kinematic analysis of the finger in motion revealed that masked primes had an influence on the pointing trajectories within 277ms of their appearance, 56ms earlier than the trajectory deviations observed in response to the visible masks. These results indicate that subliminal shapes can indeed influence the control of ongoing motor activity.