Under What Condition Does Additive Unconscious Priming Only Occur?

In the research on unconscious information processing using the masking priming method, there are still controversies regarding whether participants truly unconsciously processed the presented stimuli. The reasons for the controversies mainly stem from the intensity of the masking and the consistency of criterion adopted among different researchers. Two recent studies found that two sources of unconscious stimuli could produce an additive priming effect on the response to the target. This conclusion provides some insights into addressing the aforementioned issues. Based on the results of the additive priming effect, the present study explored the possibility of enhancing the unconscious priming effect by simultaneously presenting multiple, identical subliminal stimuli in future research characterized by strong masking and consistent criteria for unconscious processing. Unexpectedly, we found that multiple, simultaneously-presented subliminal arrows produced no additive unconscious priming effect on the response to the target except when the multiple prime arrows did not point in the same direction. Through the combined results of four experiments, we suggested that only when multiple prime stimuli have different perceptions associated with the response, can the additive effect emerge, which was explained from the perspective of neural mechanisms in the discussion. The exact- and general- additive priming effects were also distinguished and discussed.