Abstract
Three experiments were performed to examine the effects of masked colour stimuli on the response to masking stimuli. In experiment 1, two coloured squares were presented successively at the same position so that the first one could not be perceived owing to backward masking. The task was to respond to the colour of the second square as quickly as possible. The results showed that the subject's response was affected by the unperceived first square: both error rate and reaction time increased when the two squares had different colours. It was also found that reaction times for wrong responses were shorter than those for correct responses; this suggests that wrong responses occurred when the neural activation representing the first square succeeded in triggering a motor response before being suppressed. In experiment 2 we examined whether spatial attention modulated this effect or not. Eight squares (one coloured and seven white) were displayed and the spatial relation between the coloured square in the first frame (prime) and that in the second frame (target) was varied. The performance of subjects when the target location was pre-cued and when no cue was given was compared. The results indicate that in the no-cue condition the subliminal effect was observed uniformly irrespective of the spatial relation. In contrast, in the pre-cue condition the effect was diminished when prime and target occupied different positions, that is when the prime appeared outside the attended region. The result of experiment 3, with another stimulus configuration, showed a similar attentional modulation. The underlying mechanism is discussed.
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