Residual Visual Function in the Absence of the Human Striate Cortex
The organisation of visual areas in the macaque cortex suggests that different attributes of the visual image are registered in modular fashion. Thus neurones responsive to a particular attribute such as movement are associated with histologically identifiable regions of the visual cortex. Evidence for such an arrangement in humans has been obtained by functional mapping using positron emission tomography or functional magnetic resonance imaging, although species differences between the locations of areas with equivalent functional specialisation have been noted. Results of studies on human patients with cortical lesions are also consistent with the existence of functional specialisation in different visual areas. In this article, I discuss residual visual function in patients who suffer extensive field losses associated with lesions of the striate cortex. I examine in detail data for a patient, GY, who can detect transient light stimuli presented within the ‘blind’ region of his visual field. His responses to such stimuli reveal that he can discriminate between transient stimuli which differ in flicker rate or speed of movement, and he can also identify certain colours. He cannot, however, identify spatial patterns presented to his ‘blind’ field. I examine the neuronal mechanisms responsible for these responses and I discuss them with reference to the organisation of the visual cortex.
KeywordsSuperior Colliculus Cortical Lesion Striate Cortex Horizontal Meridian Orientation Discrimination
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- Damasio H. and Damasio A.R. (1989). Lesion Analysis in Neurophysiology. Oxford: University Press.Google Scholar
- Ikeda, H. and Wright. M.J. (1975). Spatial and temporal properties of’sustained’ and ‘transient’ neurones in area 17 of the cat’s visual cortex, Expl. Brain Res. 22:363–383.Google Scholar
- Riddoch, G. and Ruddock, K.H. (1991). Spatial vision after cortical lesions, in Regan, D.M. (Ed.) Spatial Vision, Vol. 10 of Vision and Visual Dysfunction, London, Macmillan, 261–289.Google Scholar
- Stiles, W.S. (1978). Mechanisms of colour vision. London: Academic Press.Google Scholar
- Teuber, H-L., Battersby, W.S. and Bender, M.B. (1960). Visual Field Defects after Penetrating Missile Wounds of the Brain. Cambridge Mass: Harvard University Press.Google Scholar
- Weiskrantz, L. (1986). Blindsight: A case study and implications. Oxford: Clarendon Press.Google Scholar
- Wyszecki, G. and Stiles, W.S. (1982). Color science: concepts and methods, quantitative data and formulae, 2nd. edn. New York: Wiley.Google Scholar
- Zeki, S. (1993). A Vision of the Brain. Oxford: Blackwell.Google Scholar