blindsight

   A term introduced in 1974 by the British neu-ropsychologists Lawrence Weiskrantz (b. 1926) et al. to denote residual vision in cases of cortical blindness, especially when there is a corresponding lack of awareness of the visual capacity on the part of the affected individual. Cortical blindness is attributed to lesions of the primary visual cortex (also referred to as V1, area 17, area OC, and striate cortex). The resulting * scotomata, varying in size from a relatively minor area to the entire hemifield (as in * hemianopia) are perceived within the visual field contralateral to the CNS lesion at hand. Individuals with lesions to V1 are not consciously aware of any visual stimuli presented within the scotomatous region. However, during the 1970s Weiskrantz et al. demonstrated that some perceptual information may nevertheless be detected by individuals suffering from cortical blindness. The geniculo-striate pathway, projecting from the retina towards V1, is the largest route into striate cortex. But it is not the only one. Empirical research has indicated that there are at least six other branches of the optic nerve that take a different route into striate cortex, and that some routes may even project into the extras-triate cortex. The residual perception of visual stimuli by individuals with blindsight is attributed to these latter pathways, i.e. the pathways projecting into the extrastriate and remaining stri-ate cortex while bypassing the geniculo-striate system.

   References

   Weiskrantz, L. (1986). Blindsight. A case study and implications. Oxford: Clarendon Press.