Neural correlates and effective connectivity of subjective colors during the Benham's top illusion: a functional MRI...

Benham's top is a rotating black-and-white pattern that fuses to form concentric rings of different colors (Prevost-Fechner-Benham subjective colors [SCs]). The underlying mechanism has been explained as resulting from local retinal cell interactions, yet the cortical processing of this illusion is largely unknown. We used rapid event-related functional magnetic resonance imaging to investigate the neural mechanisms of this SC illusion. The SCs induced when Benham's top rotated at 5 Hz were compared with perceptually matched physical color (PC) stimuli to reveal differences in both the neural substrates and their dynamic interactions by means of effective connectivity. Subjects (n = 7, all with normal vision) were required to judge whether or not they perceived color in each stimulus. The activation patterns for each condition were almost identical, but the effective connectivity from V4 to V2 and V2 to V1 was stronger during SC perception than when viewing perceptually matched PCs. All subjects perceived SC when the rotation speed of Benham's top was greater than or equal to 3 Hz, which was coupled with enhanced effective connectivity between V4 and V1. These results indicate that modulation from V4 to V2 to V1 plays a significant role in SC perception during the Benham's top illusion.