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In the 1970's Lawrence Weiskrantz PhD first popularly described this visual disorder1. The word blind in blindsight refers to something similar to retinal blindness, meaning a lack of an ability to see visual information. This lack of visual activation can be isolated to just one visual hemifield (external visual field; left or right) or it can encompass both visual hemifields. The word sight in blindsight refers to the ability to correctly guess characteristics related to a visible object. For instance, participants with blindsight have been found to correctly match objects2 or correctly guess an object's path of movement3.
Blindsight occurs from damage to an area in the rear portion of the brain called area V1. This area is located in both hemispheres of the brain. Many of the cases in which people develop blindsight or similar conditions stem from either stokes or cerebral hypoxia (loss of oxygen). When small portions of area V1 are damaged, the result can be blindspots in the visual hemifield. If only one hemisphere of V1 is completely destroyed then only one visual hemifield will be blind. Whereas if both are destroyed, then total blindness ensues. However, as it was mentioned in the previous paragraph, not all vision is lost when area V1 is completely destroyed.
The current explanation of why individuals with damage to area V1 (blindsight) maintain some ability such as detecting shapes or movements of objects is that this said ability is not controlled in area V1 but instead in surrounding cortical (brain) areas4. These surrounding cortical regions receive visual information that first passes through area V1. Thus, area V1 also serves as a switching station along the way to complete visual perception. This comes as a big surprise to many as area V1 was believed to be responsible for the ability to be consciously aware of objects. Wait, if blindsight is a result of destruction to area V1, then how can some of these other cortical areas receive the information? The answer appears to be that there is an alternative pathway that bypasses the theater of the eye (area V1)5.
As one can see or rather imagine, blindsight could directly account for the skills of the Pinball Wizard. The Pinball Wizard is "blind" and cannot consciously report the visual world. However, he can interact with aspects of the visual world such as the flippers and the movement of the ball in the pinball machine. Interestingly, a recent account of a man (TN) who experienced damaged to both V1 regions during a stroke was reported by doctors to have lost his ability to see but could control his body in a 3D environment using vision6. Dr. Gelder and colleagues tested the individual’s ability to visually interact with the world by setting up obstacles in a hall in which he was required to traverse; as he walked through the hall he avoided all obstacles that were placed in his path. A miraculous feat for a blind person indeed. However, TN's accomplishments are nowhere near as impressive as Peter Townshend's accounts of PW.
References
1. Weiskrant, L. (1996). Blindsight revisited. Current Opinion in Neurobiology, 6, 215-220.
doi:10.1016/S0959-4388(96)80075-4
2. Hamm, A. et al. (2003). Affective blindsight: intact fear conditioning to a visual cue in a cortically
blind patient. Brain, 126, 267-275. doi: 10.1093/brain/awg037
3. Ffytche, D., & Zeki, S. (2011). The primary visual cortex, and feedback to it, are not necessary for
conscious vision. Brain, 134, 247-257. doi:10.1093/brain/awq305
4. Milner, A. D., & Goodale, M. A. (2008). Two visual systems re-viewed. Neuropsychologia, 12,
774-785. doi:10.1016/j.neuropsychologia.2007.10.005
5. Schmid, M. C. et al. (2010). Blindsight depends on the lateral geniculate nucleus. Nature, 466,
373-377. doi:10.1038/nature09179
6. Gelder, B. (2008). Intact navigation skills after bilateral loss of striate cortex. Current Biology, 18,
R1128-R1129. doi:10.1016/j.cub.2008.11.002
