It is long believed that the human visual system comprises two main pathways, a ventral pathway that explicitly represents perceptual experience and a dorsal pathway that can process visual information and guide action without accompanying conscious knowledge. Evidence for this theory has primarily come from studies of neurological patients and animals. Here, we used functional Magnetic Resonance Imaging (fMRI) to measure cortical responses to invisible objects in human dorsal and ventral object-selective areas.

When low-contrast stationary images of objects are presented to the non-dominant eye and high-contrast and dynamic noise to the dominant eye intermittently, object images can be suppressed from consciousness for minutes. We found that in normal human subjects, even when they were completely unaware of the nature of visual input due to interocular suppression, dorsal cortical areas, but not ventral cortical areas, showed significant activities for different types of visual objects, with stronger responses to man-made tools than human faces. This pattern of results supports the distinct functional role of the dorsal and the ventral streams. The results also suggest that in binocular rivalry, substantial information in the suppressed eye can escape the interocular suppression, possibly traveling through the sub-cortical pathways that feed directly to the dorsal cortical regions, or through the Magnocellular pathway that is believed to be less susceptible to inter-ocular suppression.