Visual processing in the brain goes through a series of processing stages. Destruction of the first visual cortical area, primary visual cortex (or V1 or striate cortex) leads to blindness in the part of the visual field that corresponds to the damaged cortical representation. The area of blindness - known as a scotoma - is in the visual field opposite the damaged hemisphere and can vary from a small area up to the entire hemifield. In animals, the brain, or encephalon (Greek for in the head), is the control center of the central nervous system. ... Visual cortex is the term applied to both the primary visual cortex (also known as striate cortex or V1) and upstream visual cortical areas also known as extrastriate cortical areas (V2, V3, V4, V5). ... Blindness is the condition of lacking visual perception due to physiological or psychological factors. ... The word scotoma is derived from the Greek word for darkness. ...

Although individuals with damage to V1 are not consciously aware of stimuli presented in their blind field, Lawrence Weiskrantz and colleagues showed in the early 1970s that if forced to guess about whether a stimulus is present in their blind field, some observers do better than chance. This ability to detect stimuli that the observer is not conscious of can extend to discrimination of the type of stimulus (for example, whether an 'X' or 'O' has been presented in the blind field). This general phenomenon has been dubbed blindsight. Lawrence Weiskrantz is a British scientist and a Fellow of the Royal Society. ...

It is unsurprising from a neurological viewpoint that damage to V1 leads to reports of blindness. Visual processing occurs in the brain in a hierarchical series of stages (with much crosstalk and feedback between areas). As V1 is the first cortical area in this hierarchy any damage to V1 severely limits visual information passing from retina, via the LGN and then V1, to higher cortical areas. However, the route from retina through V1 is not the only visual pathway into cortex (though it is by far the largest); it is commonly thought that the residual performance of people exhibiting blindsight is due to preserved pathways into extrastriate cortex that bypass V1. What is surprising is that activity in these extrastriate areas is apparently insufficient to support visual awareness in the absence of V1. For the various types of hierarchy, see hierarchy (disambiguation) A hierarchy (in Greek: , it is derived from -hieros, sacred, and -arkho, rule) is a system of ranking and organizing things or people, where each element of the system (except for the top element) is subordinate to a single other element. ... Human eye cross-sectional view. ... Grays FIG. 719– Hind- and mid-brains; postero-lateral view. ... Visual cortex is the term applied to both the primary visual cortex (also known as striate cortex or V1) and upstream visual cortical areas also known as extrastriate cortical areas (V2, V3, V4, V5). ... Consciousness is a quality of the mind generally regarded to comprise qualities such as subjectivity, self-awareness, sentience, sapience, and the ability to perceive the relationship between oneself and ones environment. ...

References

• Danckert, J. & Rossetti, Y. (2005). "Blindsight in action: what can the different sub-types of blindsight tell us about the control of visually guided actions?". Neurosci Biobehav Rev 29 (7): 1035–1046.
• Stoerig, P. & Cowey, A. (1997). "Blindsight in man and monkey". Brain 120: 535–559.
• Weiskrantz, L (1986). Blindsight: A case study and its implications. Oxford, Oxford University Press. ISBN 0-19-852192-8.