PURPOSE: The serial reaction time (SRT) task has been widely used to investigate whether sequence learning can occur without awareness. However, in most of the SRT tasks, the stimuli can be perceived consciously, and the question is whether people can acquire perceptual or motor sequence knowledge at the unconscious level. It remains unclear whether people can acquire perceptual knowledge when the stimuli in a sequence are invisible or subliminal.
METHODS: In this study, we used continuous flash suppression (CFS) method to explore whether people can learn the serial order of subliminal stimuli. During the familiarization phase, distinct flash patterns were presented to the dominant eye and novel symbols of four triplets were presented to the other eye in the subliminal condition, while the flash patterns and symbols were presented simultaneously in both eyes in the visible control condition. During the test phase, a continuous stream of 12 visible symbols was presented to the same eye as in the familiarization phase in a rapid serial visual presentation (RSVP) task, and participants were asked to press a key when a target symbol was presented.
RESULTS: The results showed that the detection latency was faster when the target was the third symbol of the triplets than it was the first symbol of the triplets in the CFS condition, but there was no such location effect in the control condition.
CONCLUSIONS: The results indicate that perceptual sequence learning can occur even when the stimuli are invisible, although people do not express sequence learning effects when the stimuli are visible.