The Riddoch syndrome: insights into the neurobiology of conscious vision

Brain : a Journal of Neurology
S Zeki, D H ffytche

Abstract

We have studied a patient, G.Y., who was rendered hemianopic following a lesion affecting the primary visual cortex (area VI), sustained 31 years ago, with the hope of characterizing his ability to discriminate visual stimuli presented in his blind field, both psychophysically and in terms of the brain activity revealed by imaging methods. Our results show that (i) there is a correlation between G.Y.'s capacity to discriminate stimuli presented in his blind field and his conscious awareness of the same stimuli and (ii) that G.Y.'s performance on some tasks is characterized by a marked variability, both in terms of his awareness for a given level of discrimination and in his discrimination for a given level of awareness. The observations on G.Y., and a comparison of his capacities with those of normal subjects, leads us to propose a simple model of the relationship between visual discrimination and awareness. This supposes that the two independent capacities are very tightly coupled in normal subjects (gnosopsia) and that the effect of a VI lesion is to uncouple them, but only slightly. This uncoupling leads to two symmetrical departures, on the one hand to gnosanopsia (awareness without discrimination) and on the other to agnos...Continue Reading

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