Effects of masked stimuli on motor activation: Behavioral and electrophysiological evidence

Three experiments investigated the influence of unperceived events on respo nse activation. Masked primes were presented before a target. On compatible trials, primes and targets were identical; on incompatible trials, opposit e responses were assigned to-them. Forced-choice performance indicated that prime identification was prevented by the masking procedure, but overt per formance and motor activation as mirrored by the lateralized readiness pote ntial (LRP) were systematically influenced by the prime. The direction of t hese effects was unexpected: Performance costs for compatible and performan ce benefits for incompatible trials were obtained relative to a neutral tri al condition. The LRP revealed a sequential pattern of motor activation. A partial activation of the response corresponding to the prime was followed by a reverse activation pattern. It is argued that these effects primarily reflect an inhibition of the response initially triggered by the prime.