Contextual Information Modulates Unconscious Visual Processing in Early Visual Cortex

Human visual perception is context dependent. Previous studies have demonstrated that the conscious representation of a variety of visual stimuli can be altered by contextual information. Whether and to what extent contextual modulation could also take effect on the processing of invisible stimuli is largely unknown. Here we probed this question using two types of context-dependent visual illusions (i.e., Ebbinghaus illusion and Ponzo illusion) combined with the interocular suppression paradigm. The Ebbinghaus and Ponzo illusions, though correlated with the primary visual cortex (V1), are respectively mediated by lateral connections within V1 and feedback projections from higher brain areas to V1. Here we selectively rendered the central targets of the two illusion figures invisible while leaving their surrounding inducers intact. In the Ebbinghaus illusion, we found that the central target broke from suppression sooner when surrounded by smaller relative to larger inducers. Moreover, the illusion strength predicted the suppression time difference between these conditions across participants. In the Ponzo illusion, however, the processing of the invisible target was not influenced by the contextual inducers. These results provide strong evidence that contextual information can modulate the unconscious visual processing, and such modulation occurs in the early visual processing stream independent of feedback influences. Meeting abstract presented at VSS 2014