Document Detail

Achromatic parvocellular contrast gain in normal and color defective observers: Implications for the evolution of color vision.
MedLine Citation:
PMID:  16962004     Owner:  NLM     Status:  MEDLINE    
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.
Margaret Lutze; Joel Pokorny; Vivianne C Smith
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Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Visual neuroscience     Volume:  23     ISSN:  0952-5238     ISO Abbreviation:  Vis. Neurosci.     Publication Date:    2006 May-Aug
Date Detail:
Created Date:  2006-09-11     Completed Date:  2006-10-18     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  8809466     Medline TA:  Vis Neurosci     Country:  England    
Other Details:
Languages:  eng     Pagination:  611-6     Citation Subset:  IM    
Department of Ophthalmology and Visual Science, The University of Chicago, Chicago, Illinois 60637, USA.
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MeSH Terms
Color Perception / physiology*
Color Perception Tests / methods
Color Vision Defects / physiopathology*
Contrast Sensitivity / physiology*
Pattern Recognition, Visual / physiology
Photic Stimulation / methods
Psychophysics / methods
Time Factors
Vision, Ocular / physiology*
Visual Pathways / physiopathology
Grant Support

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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