COLOR-PERCEPTION PROFILES IN CENTRAL ACHROMATOPSIA

Central achromatopsia is an impairment of color perception caused by d amage to the visual association cortex. Its psychophysical underpinnin gs remain poorly defined. We report our attempt to characterize the de fect along critical dimensions of color space, taking advantage of the same standardized tasks that allow detailed profiles in patients with retinal cone defects. We studied two patients. The results in patient 1 showed that perceptual color space was collapsed along the red-gree n (R-G) and short-wavelength-sensitive cone (S-cone) dimensions but th at discriminations along achromatic dimensions were relatively preserv ed. Additional observations showed that the defect was dependent on ta rget size, and that processing of surface and light source effects tha t differ from color (eg, transparency) was intact. Patient 2 showed a less severe color processing defect involving signals arising from the S-cones of the retina, although an R-G defect was also present. The p rofiles in these two patients demonstrate that central achromatopsia e ncompasses a range of color processing impairments with varied psychop hysical characteristics.