Biomaterial Database

Achromatic parvocellular contrast gain in normal and color defective observers: Implications for the evolution of color vision. 2006

Margaret Lutze, and Joel Pokorny, and Vivianne C Smith

Department of Ophthalmology and Visual Science, The University of Chicago, Chicago, Illinois 60637, USA.

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.

UI	MeSH Term	Description	Entries
D008251	Macaca	A genus of the subfamily CERCOPITHECINAE, family CERCOPITHECIDAE, consisting of 16 species inhabiting forests of Africa, Asia, and the islands of Borneo, Philippines, and Celebes.	Ape, Barbary,Ape, Black,Ape, Celebes,Barbary Ape,Black Ape,Celebes Ape,Macaque,Apes, Barbary,Apes, Black,Apes, Celebes,Barbary Apes,Black Apes,Celebes Apes,Macacas,Macaques
D008297	Male		Males
D010364	Pattern Recognition, Visual	Mental process to visually perceive a critical number of facts (the pattern), such as characters, shapes, displays, or designs.	Recognition, Visual Pattern,Visual Pattern Recognition
D010775	Photic Stimulation	Investigative technique commonly used during ELECTROENCEPHALOGRAPHY in which a series of bright light flashes or visual patterns are used to elicit brain activity.	Stimulation, Photic,Visual Stimulation,Photic Stimulations,Stimulation, Visual,Stimulations, Photic,Stimulations, Visual,Visual Stimulations
D011601	Psychophysics	The science dealing with the correlation of the physical characteristics of a stimulus, e.g., frequency or intensity, with the response to the stimulus, in order to assess the psychologic factors involved in the relationship.	Psychophysic
D003117	Color Vision Defects	Defects of color vision are mainly hereditary traits but can be secondary to acquired or developmental abnormalities in the CONES (RETINA). Severity of hereditary defects of color vision depends on the degree of mutation of the ROD OPSINS genes (on X CHROMOSOME and CHROMOSOME 3) that code the photopigments for red, green and blue.	Achromatopsia,Color Blindness,Monochromatopsia,Color Blindness, Acquired,Color Blindness, Blue,Color Blindness, Green,Color Blindness, Inherited,Color Blindness, Red,Color Blindness, Red-Green,Color Vision Deficiency,Deutan Defect,Protan Defect,Tritan Defect,Achromatopsias,Acquired Color Blindness,Blindness, Color,Blue Color Blindness,Color Blindness, Red Green,Color Vision Defect,Color Vision Deficiencies,Defect, Color Vision,Defect, Deutan,Defects, Color Vision,Deficiencies, Color Vision,Deficiency, Color Vision,Green Color Blindness,Inherited Color Blindness,Red Color Blindness,Red-Green Color Blindness,Vision Defect, Color,Vision Defects, Color,Vision Deficiencies, Color,Vision Deficiency, Color
D003118	Color Perception	Mental processing of chromatic signals (COLOR VISION) from the eye by the VISUAL CORTEX where they are converted into symbolic representations. Color perception involves numerous neurons, and is influenced not only by the distribution of wavelengths from the viewed object, but also by its background color and brightness contrast at its boundary.	Color Perceptions,Perception, Color,Perceptions, Color
D003119	Color Perception Tests	Type of vision test used to determine COLOR VISION DEFECTS.	Color Perception Test,Perception Test, Color,Perception Tests, Color,Test, Color Perception,Tests, Color Perception
D005075	Biological Evolution	The process of cumulative change over successive generations through which organisms acquire their distinguishing morphological and physiological characteristics.	Evolution, Biological
D006801	Humans	Members of the species Homo sapiens.	Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man