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Zeki (1993): Human pathological conditions (p.73) — Lesions in specific cortical areas produce correspondingly specific visual syndromes.

l lesions to area V4 lead to achromatopsia, in which patients see only in shades of gray. This is different from simple colour blindness: not only do the patients fail to see or know the world in colour, they cannot even recall colours from a time before the lesion. But if their retinas and V1 regions are healthy, their knowledge of form, depth and motion remains intact.

l lesions to area V5 produces akinetopsia, in which patients neither see nor understand the world in motion. While at rest, objects may be perfectly visible to them, but motion causes the objects to vanish. But the other attributes of vision remain unscathed.

l No one has reported a complete and specific loss of form vision: area V3 forms a ring around V1 and V2; a lesion large enough to destroy V3 would probably destroy V1 as well and cause blindness. But —

l Some patients with lesions in prestriate cortex have a degree of form imperception. They have greater difficulty identifying stationary forms than when the same forms are in motion: they often prefer watching television to “real” vision because television is dominated by moving images. They often resort to the strategy of moving their heads when identifying stationary objects.

l a syndrome, “Chromatopsia”, may follow diffuse cortical damage caused by carbon monoxide poisoning. These patients have vision that is severely comprised in all respects except one: their colour vision is affected only mildly if at all. The often try to identify all objects solely on the basis of colour: e.g. misidentifying all blue objects as “ocean”.

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