Human visual cortex responds to invisible chromatic flicker.
When two isoluminant colors alternate at frequencies of 25 Hz or higher, observers perceive only one fused color. Chromatic flicker beyond the fusion frequency induces flicker adaptation in human observers and stimulates monkey V1 neurons. Here we use functional magnetic resonance imaging (fMRI) to show that many human visual cortical areas, with the exception of VO, can distinguish between fused chromatic flicker and its matched nonflickering control. This result supports the existence of significant intracortical temporal filtering of high-frequency chromatic information. The result also suggests that a considerable difference in cortical activation in many visual cortical areas does not necessarily lead to different conscious experiences.
Jiang
Yi
Y
Department of Psychology, University of Minnesota, 75 E. River Rd., Minneapolis, Minnesota 55455, USA.
Zhou
Ke
K
He
Sheng
S
D001931:Brain Mapping; D003116:Color; D003118:Color Perception / Q000502:physiology*; D015350:Contrast Sensitivity; D004192:Discrimination, Psychological; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005425:Flicker Fusion / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging; D008297:Male; D010100:Oxygen / Q000097:blood; D010775:Photic Stimulation / Q000379:methods; D014793:Visual Cortex / Q000098:blood supply / Q000502:physiology*
D010100:Oxygen