Achromatic parvocellular contrast gain in normal and color defective observers: Implications for the evolution of color vision
- 1 May 2006
- journal article
- research article
- Published by Cambridge University Press (CUP) in Visual Neuroscience
- Vol. 23 (3-4), 611-616
- https://doi.org/10.1017/s0952523806233078
Abstract
The PC pathway conveys both chromatic and achromatic information, with PC neurons being more responsive to chromatic (L−M) than to achromatic (L+M) stimuli. In considering the evolution of color vision, it has been suggested that the dynamic range of chromatic PC-pathway processing is tuned to the chromatic content of the natural environment. Anomalous trichromats, with reduced separation of their L- and M-cone spectral sensitivities, have diminished chromatic input to PC-pathway cells. Dichromats, with absent L or M cones, should have no chromatic input to PC-pathway cells. Therefore, the PC-pathway dynamic range of color defectives should be released from any constraint imposed by the chromatic environment. Here we ask whether this results in compensatory enhancement of achromatic PC-pathway processing in color defectives. This study employed a psychophysical method designed to isolate PC-pathway processing using achromatic stimuli. In a pulsed-pedestal condition, a four-square stimulus array appeared within a uniform surround. During a trial, one of the test squares differed from the other three, and the observer's task was to choose the square that was different. A four-alternative, forced-choice method was used to determine thresholds as a function of the contrast of the four-square array to the surround. Seven color defective and four normal observers participated. Results showed no systematic differences between normals and color defectives. There was no enhancement of achromatic processing as compensation for reduced chromatic processing in the PC-pathway system in color defectives. From physiological recordings, PC-pathway achromatic contrast gains of dichromatic and trichromatic New World primates and trichromatic Old World macaques have also been shown to be similar to each other. Our study and the animal studies imply that PC-pathway contrast gain parameters were regulated by factors other than the environmental chromaticity gamut, and may have arisen in a nontrichromatic common ancestor to both Old and New World primates.Keywords
This publication has 18 references indexed in Scilit:
- Chromatic and spatial properties of parvocellular cells in the lateral geniculate nucleus of the marmoset (Callithrix jacchus)The Journal of Physiology, 2004
- Spatial frequency processing in inferred PC- and MC-pathwaysVision Research, 2003
- Psychophysical Correlates of Parvo- and Magnocellular FunctionPublished by Oxford University Press (OUP) ,2003
- Pulse and steady-pedestal contrast discrimination: effect of spatial parametersVision Research, 2001
- Functional consequences of the relative numbers of L and M conesJournal of the Optical Society of America A, 2000
- Psychophysical signatures associated with magnocellular and parvocellular pathway contrast gainJournal of the Optical Society of America A, 1997
- Colour is what the eye sees bestNature, 1993
- Luminance and chromatic modulation sensitivity of macaque ganglion cells and human observersJournal of the Optical Society of America A, 1990
- The primate retina contains two types of ganglion cells, with high and low contrast sensitivity.Proceedings of the National Academy of Sciences, 1986
- Evaluation of single-pigment shift model of anomalous trichromacy*Journal of the Optical Society of America, 1977