Abstract
Continuous Flash Suppression (CFS) is a technique to render stimuli presented to one eye invisible for prolonged periods (Tsuchiya and Koch, 2005). A constant visual stimulus is presented to the non-dominant eye while the dominant eye is presented with random flashing color patterns at about 10 Hz. The color patterns dominate perception, blocking the constant stimulus from conscious awareness. As in binocular rivalry, however, these constant stimuli eventually become consciously available. In our study, we presented subjects with four categories of stimuli under CFS: faces, inverted faces, cars and sine-wave gratings. They indicated their visual percept on each five-second trial by holding one key while consciously perceiving only the random patterns and holding another key while perceiving a stimulus. We found that faces became consciously available for a significantly higher percentage of the presentation time than other stimuli of the same size, luminance, and contrast. Upright faces were visible significantly more of the time than inverted faces. Both upright and inverted faces were visible significantly more of the time than cars and sine-wave gratings. This result suggests that the effectiveness of the CFS paradigm is affected by high-level stimulus characteristics, which raises questions about the nature of CFS suppression. On the other hand, assuming low level blockage of visual information under CFS, our finding might suggest low-level cortical representation of face specific features or parts.