Peripheral human colour vision; from cone contrast to colour perception

Access to files

•   FULL-TEXT.PDF (pdf)

Abstract

It is well known that the colour preferences of ganglion and LGN cells do not match the four perceptually simple colours red, green blue and yellow. It is also known that although colour perception is distorted in the peripheral visual field, there are four hues that appear stable with eccentricity. These are defined as peripherally invariant hues. Both of these observations must in some way reflect the physiological substrate of neurons at different stages of the primary visual pathway. The experiments described here are aimed at understanding the link between the physiology and the perception of colour by studying the characteristics of peripheral colour visionThe following questions have been addressed; i) to what extent does colour matching rely on the retinal physiological substrate? ii) what is the reason for the discrepancy between invariant and unique green and how is cone contrast linked to this paradox? iii) how are the `special' hues (invariant and unique) related to human evolution? iv) how does peripheral colour vision vary between males and females?An asymmetric colour matching paradigm and a colour naming task have been employed. In the colour matching task, 24 chromatic axes of variable purity are used. Observers match the chromaticity of a 3 degree peripheral spot with that of a 1 degree parafoveal spot. The results are expressed in terms of hue rotation, saturation match and cone contrast. In the colour naming experiment the observers name 40 chromatic axes as either red, blue, green or yellow and colour naming functions are derived. The central maxima of these functions are defined as the unique hues. The results suggest that colour matching and cone opponency reflect the characteristics of the retinal neural network as they exhibit nasal-temporal asymmetries, similar to known physiological asymmetries. Although three of the peripherally invariant hues match the unique counterparts, invariant and unique green are markedly different for all observers. In an important control experiment unique hues are shown to be stable with eccentricity and purity. This confirms that these attributes are not confounding factors for the observed discrepancy between invariant and unique green. Unlike for the other ‘special’ hues the RMS cone contrast of invariant green differs markedly between parafoveal and peripheral targets. It is likely that the cone contrast remains unchanged only if the stimuli excite the same number of cones.Two invariant and two unique hues (blue and yellow) fall on the daylight locus suggesting that discrimination in these regions of the colour space is strongly influenced by terrestrial illumination. Moreover, the inter-individual variability is found to be minimised around the daylight locus showing that the blue-yellow system is more stable across colour normal populations than the red-green system. A statistically significant difference is demonstrated between the peripheral colour vision of males and females. This may be attributed to the M-cone polymorphism which in addition to X-chromosome inactivation, results in more than three cone types in the female retina.

Keyword(s)

color vision; daylight and colour vision; evolution; male female differences; nasal temporal asymmetries ; peripheral retina; unique hues

Bibliographic metadata

Institutional metadata

Record metadata