Abstract: It is argued that the brain can process single subliminal stimulus. Furthermore, recent research showed the evidence of an integration between multiple subliminal stimuli. However, as for the high level processing such as semantic word, recently, some studies did not reveal any integration between different words/characters when the words/characters were presented in sequence, but the results showed an integration effect when the words/characters were presented simultaneously. In these studies, the sequentially presented subliminal prime words were displayed at the same location. There is a possibility that the different stimuli presented sequentially at the same spatial position could produce interferential neural activity that might influence the unconscious integration. Therefore, in the present study, the advantage of simultaneous presentation (different spatial presentation positions) was used to investigate whether there can be unconscious semantic integration between different Chinese words presented in sequence. Specifically, two masked Chinese words of same or different categories (fruit or tool) were presented as prime on both sides, followed by two Chinese words also of same or different categories in the target. Participants were asked to judge whether the paired target words were of the same or different categories. The different time interval between the two subliminal prime words was controlled in experiment 1 (0 ms) and in experiment 2 (32ms). In addition, experiment 3 was designed to exclude the visual residue of the first prime word in experiment 1.The results indicated that there existed the unconscious semantic category integration effect in experiment 1. But there was no unconscious semantic category integration effects in experiment 2. Meanwhile, in Experiment 3, no integration effect was observed, which indicated that the unconscious integration effect observed in experiment 1 was promoted by visual residue of the first prime word. Overall, the results of the three experiments revealed that the integration of sequential subliminal semantic information was difficult to occur, and the semantic relation between the two subliminal words could only be unconsciously integrated under the special conditions of simultaneous presentation, suggesting the importance of the short-range temporal window for the unconscious integration of high-level semantic relations.

Key words: unconscious integration, sequential integration, semantic category relations