Visual Cortical Activity Evoked by Unconscious Chromatic Flicker
35.14, Sunday, 18-May, 5:15 pm - 7:15 pm, Talk Room 1
Xiuling Zhang1,2, Yi Jiang3; 1School of Psychology, Northeast Normal University, Changchun 130024, P.R.China, 2Department of Psychology, University of Maryland, College Park, MD, 20740, US, 3Institute of Psychology, Chinese Academy of Sciences, Beijing 100101, P. R. China
Introduction When two isoluminant colors alternate at fusion frequency (25 Hz) or higher, observers perceive only one fused color. Recent fMRI research shows that many human visual cortical areas can distinguish between fused chromatic flicker and its matched nonflickering control. Here we use ERP method to investigate the C1 component evoked by fused chromatic flicker and its static control. Methods Sixteen people participated in the study. We used 2(color: fused chromatic flicker vs. static control) ×2 (visual field: upper left vs. lower right) within subject design. The fused chromatic flicker is two isoluminant colors (red and green) alternating at frequency of 30 Hz. The nonflickering control color is luminance matched static yellow. Each trial started with a fixation for 800-1200ms, then the color stimuli presented for 100ms. Participants were required to respond to the occasional size change of a central fixation. Results Our results showed that the C1 was affected by the invisible stimuli with increased amplitude to fused chromatic flicker than to its static control. At PZ, POZ, OZ, fused color evoked a higher peak amplitude C1 for both upper left (F(1, 15) = 12.32, p<0.005) and lower right visual field (F(1, 15) = 6.56, p<0.05). There is no significant difference between the amplitude of both P1 and N1 component evoked by fused color and static color. A forced choice study show that participants could not discriminate the fused color and static control. Conclusion The results showed that primary visual cortex could distinguish between invisible fused chromatic flicker and its matched nonflickering control suggesting that a considerable difference in visual cortical activation does not necessarily lead to different conscious experiences.