Perception of colour in unilateral tritanopia.

Abstract

The unilateral tritanope described in the previous paper (Alpern, Kitahara & Krantz, 1983) was able to match every narrow‐band light presented to his tritanopic eye with lights from a tristimulus colorimeter viewed in the adjacent field by the normal eye. In two regions of the spectrum (called isochromes) physically identical lights appeared identical to the observer's two eyes. One isochrome was close to ‘blue’ for the normal eye, the other was in the long‐wave spectral region seen by the normal eye predominantly as ‘red'. Between these isochromes the normal eye required less than spectral purity to match, dropping to near zero purity at 560‐570 nm. A mixture of the two isochromes that appeared purple to the normal eye appeared neutral to the tritanopic eye. Hence dichoptic matches grossly violate Grassmann's additivity law. For the normal eye colour naming conformed to typical normal results. For the tritanopic eye the results were coherent with those found by dichoptic matching: the spectrum was divided into two regions by the achromatic neutral band. To the short‐wave side, only the colour names ‘blue’ and ‘white’ were ever used. To the long‐wave side the predominant colour names were ‘red’ and ‘white’ with some ‘yellow'. Spectral lights appeared neither ‘red‐blue’ nor greenish. Surrounding the test with an annulus either 430 nm, 650 nm, or a mixture of these, fails to induce any greenish appearance, although the achromatic band shifted in the expected directions. It is concluded that there must be exactly three functionally independent, essentially non‐linear central codes for colour perception, and that these codes are different from those suggested in existing theories of colour perception.

Contribution of S opponent cells to color appearance

“…Also in accord with our data are the reports (23,24) that unilateral tritanopic observers see the entire short-wavelength half of the spectrum as uniformly greenish-blue in their tritanopic eye. That the 90°-270°color range (equivalent to dominant wavelengths of about 400-570 nm with reference to illuminant C) was seen as a greenish-blue in the absence of S input is not in accord with an LGN-based color vision model that assumes that the S o cells form the basis for the yellow-blue color system.…”

Classical tritanopia

“…A detailed report of ophthalmological examinations is presented in the Appendix. In brief, he is a 26-year-old white male with no previous history of visual abnormality, who, 2 years before, had an acute episode of central serous chorio-retinopathy ( Alpern, Kitahara & Krantz (1983).…”

Dichromatic color perception in a two stage model: Testing for cone replacement and cone loss models

“…Results reported from experiments show that for each type of dichromacy it is possible to find two wavelengths regions of the visual spectrum, where the individuals register a match in color perception between both eyes for (close to) monochromatic stimuli [16][17][18]. Wavelengths with such characteristics are called isochromes [16].…”

“…Results reported from experiments show that for each type of dichromacy it is possible to find two wavelengths regions of the visual spectrum, where the individuals register a match in color perception between both eyes for (close to) monochromatic stimuli [16][17][18]. Wavelengths with such characteristics are called isochromes [16]. Isochromes for protanopes and deuteranopes can be found in stimuli with wavelengths around 475nm and 575nm, where the perceived colors are reported as blue and yellow, while for tritanopes, the isochromes are found in 485nm, perceived as blue-green and 660nm, which is labeled as red [3].…”