Cortical responses to invisible objects in the human dorsal and ventral pathways.

The primate visual system is believed to comprise two main pathways: a ventral pathway for conscious perception and a dorsal pathway that can process visual information and guide action without accompanying conscious knowledge. Evidence for this theory has come primarily from studies of neurological patients and animals. Using fMRI, we show here that even though observers are completely unaware of test object images owing to interocular suppression, their dorsal cortical areas demonstrate substantial activity for different types of visual objects, with stronger responses to images of tools than of human faces. This result also suggests that in binocular rivalry, substantial information in the suppressed eye can escape the interocular suppression and reach dorsal cortex.