A case study of cortical colour "blindness" with relatively intact achromatic discrimination.

Abstract

SUMMARY A patient is described whose most striking visual disorder was a grossly impaired ability to discriminate between different colours (hues) that were matched for brightness. In contrast his ability to discriminate between different neutral greys presented in the same fashion was much less abnormal, even though the greys were perceptually difficult. Although visual acuity was reduced and visual fields were constricted, and the patient's memory was moderately impaired, these associated symptoms could not themselves be the cause of his unusual colour vision. The patient had the symptoms of cerebral achromatopsia, and the relative preservation of his form vision (when his reduced acuity is taken into account) and his achromatic vision supports the view that the many different visual cortical areas recently demonstrated in the brains of monkeys, and presumed to exist in man, have a perceptual specialisation that matches their physiological differences.Cerebral achromatopsia is a severe disturbance of the perception of colour caused by cerebral cortical damage. The patient has great difficulty in discriminating between hues and commonly complains that the world looks drained of colour. Although the term achromatopsia implies that vision has become colourless, colours may still be perceived, albeit faintly (that is, they are desaturated). The condition contrasts sharply with other acquired disorders of colour vision where the primary fault is a disconnexion syndrome or a semantic disorder involving the use of colour words (see reference I for review) or an impaired ability to remember perceived colours for more than a few seconds.2 There are several reports which suggest that cerebral achromatopsia can appear without accompanying deficits in the perception of depth, form, acuity, movement or any other psychophysical dimension.34 However, the disturbances are often accompanied by apperceptive visual agnosia' and the cortical damage invariably involves

Deficits in face perception in the amnestic form of mild cognitive impairment

“…However, cerebral achromatopsia from lingual and fusiform lesions usually affects hue and saturation discrimination, with preservation of lightness perception [30][31][32]. Indeed, this was the rationale for choosing to modulate lightness rather than color in our paradigm [28].…”

Contributions of magno- and parvocellular channels to conscious and non-conscious vision

“…Moreover, an achromatopsic patient investigated by Heywood et al [39], while grossly impaired in discriminating isoluminant hues, was able to discriminate different achromatic greys. This is consistent with Wang et al's [33] findings in monkey indicating the existence of separate luminance and colour processing areas within V2 thin-stripe surface-processing modules.…”

Achromatopsia, color vision, and cortex

“…Cerebral achromatopsia refers to the condition in which brain damage results in a loss of color vision [16][17][18][19][20][21][22]. Color imperceptions produced by cerebral lesions can be of varied nature and differ in their degree of recovery [23].…”

“…Color disorders of retinal origin can be revealed using the Ishihara pseudoisochromatic plates. Patients with achromatopsa are able to read some or all of the plates [17,21] or can only do so under particular testing conditions, notably increased viewing distance [18][19][20]. (Increasing the viewing distance reduces the extent to which the optics of the eye and the visual system can resolve fine detail in an image.…”