[Behavioral effect of a subliminal (masked) signal]

Three experiments investigated the influence of a non-consciously perceived visual signal on motor reaction time when subjects were exposed to a stimulus contingency according to the general rules of the Pavlovian conditioning procedure. Conscious perception was prevented by meta-contrast backward masking. A total of 128 adult subjects had to discriminate between two imperative stimuli by means of a choice reaction. Each imperative stimulus was signalled by a different brief figural stimulus (signal). In Experiment 1, the signal was not masked during the training period but was masked during the subsequent test period. The subjects were unable to report the stimulus-contingency to which they were exposed during the training period. Inspite of masking, the signal remained efficient, i.e., reaction time increased when the stimulus-contingency was inverted. In Experiment 2, the signal was masked during the training period but not during the test period. There was no evidence that the masked signal influenced reaction time. In Experiment 3, during the training period, the signal was followed by a distractor instead of the mask. As a result, the distractor prevented the signal from becoming an efficient stimulus similar to the mask in Experiment 2. The data suggest that preattentive (non-conscious) processing is sufficient for a previously learned signal to influence reaction time. On the other hand, focussed attention seems to be a precondition for a stimulus becoming an efficient signal.