Primary visual cortex: awareness and blindsight.
The primary visual cortex (V1) is the principal telencephalic recipient of visual input in humans and monkeys. It is unique among cortical areas in that its destruction results in chronic blindness. However, certain patients with V1 damage, though lacking visual awareness, exhibit visually guided behavior: blindsight. This phenomenon, together with evidence from electrophysiological, neuroimaging, and psychophysical experiments, has led to speculation that V1 activity has a special or direct role in generating conscious perception. To explore this issue, this article reviews experiments that have used two powerful paradigms--stimulus-induced perceptual suppression and chronic V1 ablation--each of which disrupts the ability to perceive salient visual stimuli. Focus is placed on recent neurophysiological, behavioral, and functional imaging studies from the nonhuman primate that shed light on V1's role in conscious awareness. In addition, anatomical pathways that relay visual information to the cortex during normal vision and in blindsight are reviewed. Although the critical role of V1 in primate vision follows naturally from its position as a bottleneck of visual signals, little evidence supports its direct contribution to visual awareness.
Section on Cognitive Neurophysiology and Imaging, Laboratory of Neuropsychology, National Institute of Mental Health, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland 20892, USA. leopoldd@mail.nih.gov
David A
DA
Leopold
D000818:Animals; D001364:Awareness / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods / Q000523:psychology*; D003243:Consciousness / Q000502:physiology; D006801:Humans; D008959:Models, Neurological; D009433:Neural Inhibition / Q000502:physiology; D009778:Occipital Lobe / Q000502:physiology; D014793:Visual Cortex / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology; D014796:Visual Perception / Q000502:physiology*