关键词: 连续闪烁抑制, 无意识加工, 运动, 伪装, 透明度混合

Abstract:

Continuous flash suppression (CFS) is one of the common methods to study unconscious visual processing. In the regular CFS paradigms used in previous studies, dynamic or high contrast image sequences (such as the Mondrian pattern sequences) are presented to one eye as masks. Meanwhile, a static or lower contrast target is presented to the opposite eye, which can be rendered invisible by the masks for a short period of time. The present study was designed to explore whether the CFS can effectively block the conscious processing of multiple moving targets. Inspired by the camouflage of chameleons in the nature, we proposed a novel CFS paradigm (which we call the “chameleon” paradigm). By using the alpha blending algorithm, we ensured the color of the targets to be consistent with the corresponding regions of the CFS masks at any moment. We then tested whether the “chameleon” paradigm can obscure the targets’ motion information from awareness more effectively than the regular CFS paradigm.

We randomly recruited eight participants. Their dominant eyes were presented with the regular CFS masks, meanwhile the nondominant eyes were presented with ten spatially non-overlapping squares as the targets which moved either upwards or downwards at a constant velocity. Each square had one second of lifetime. Thus, for each square, after every one second of movement, its position was reset, and then it continued to move in the same direction at the same speed. In each trial, the target squares were presented for ten seconds (refreshing their positions ten times) at most. By manipulating the degree of color consistency between the targets and the masks, a total of four experimental conditions were included, with a “chameleon” condition and three control conditions. Participants were instructed to report the moving direction of the targets on seeing the targets by pressing a corresponding button. The program recorded both the response accuracy and the response time since the start of a trial (i.e. the time required for the targets to break into awareness, aka the breakthrough time). We also calculated the percentage of trials where the targets broke into awareness, which was called the breakthrough rate.

The results showed that the “chameleon” paradigm allowed the CFS masks to efficiently block the conscious processing of multiple moving targets. Specifically, as compared to the three control conditions with less degree of color consistency between the targets and the CFS masks, the breakthrough rate was significantly lower under the “chameleon” condition where the color of the targets was fully consistent with the CFS masks. No significant differences were found for the breakthrough rate between the three control conditions. Moreover, according to the grand average data, in the “chameleon” condition the moving targets could break into awareness within 10 s in only about 25% of the trials. For the three control conditions, this probability increased to more than 80%, suggesting an overwhelming advantage of the “chameleon” paradigm in rendering multiple moving targets invisible.

Another advantage of the “chameleon” paradigm is that it does not require the CFS masks to contain any motion information resembling the targets, thereby it ensures that the measurement of unconscious visual motion processing is exclusively from the target. Compared with the idea of modifying CFS masks in the literature, our method is believed to have broader applicability. Therefore, we recommend the “chameleon” paradigm a useful tool for future investigations of unconscious visual motion information processing.

Key words: continuous flash suppression, unconscious processing, motion, camouflage, alpha blending