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MECHANISMS OF COLOR VISION

SOME OF THE RECENT ADVANCES CONCERNING COLOR VISION ARE BRIEFLY DESCRIBED. THE INITIAL NON-OPTICAL EVENT IN THE VISUAL PROCESS IS THE ABSORPTION OF LIGHT IN THE VISUAL PHOTOPIGMENTS CONTAINED WITHIN THE OUTER SEGMENTS OF PHOTORECEPTORS LOCATED IN THE RETINA OF THE EYE. PRESUMPTIVE EVIDENCE HAS BEEN AVAILABLE FOR MANY YEARS TO SUGGEST THAT THREE CLASSES OF PHOTOPIGMENT, EACH HAVING A DIFFERENT SPECTRAL SENSITIVITY, MUST BE PRESENT IN THE PHOTORECEPTORS TO PROVIDE THE BASIS OF CHROMATIC DISCRIMINATION. WITHIN THE LAST DECADE, THE EXISTENCE OF SEPARATE CLASSES OF CONE PIGMENT HAS DEFINITELY BEEN ESTABLISHED BY TWO KINDS OF PHYSICAL EXPERIMENT: (1) UTILIZING A TECHNIQUE KNOWN AS RETINAL DENSITOMETRY, AND (2) SPECTROPHOTOMETRY AT THE LEVEL OF THE SINGLE CELL KNOWN AS MICROSPECTROPHOTOMETRY. THESE METHODS ARE ANLAYZED AND REVIEWED. THE EXPERIMENTS INDICATE THAT THERE IS NO DOUBT ABOUT THE EXISTENCE OF THREE OR MORE CLASSES OF PHOTOPIGMENT IN CONES. THE EVIDENCE SUGGESTS THAT A SINGLE CONE CONTAINS ONLY ONE TYPE OF PIGMENT RATHER THAN A MIXTURE. THE DEVELOPMENT OF OPPONENT-COLORS THEORIES ARE DISCUSSED. EXPERIMENTS INDICATE THAT OPPONENT-COLOR COMPUTATION IS DONE IN THE PRIMATE RETINA WHICH IS INDICATED BY OPPONENT RESPONSES IN THE LATERAL GENICULATE BODY, A PRINCIPAL RELAY STATION BETWEEN THE EYE AND THE BRAIN. THE FOLLOWING PICTURE ACCOUNTS FOR THE ENCODING AND TRANSMISSION OF AT LEAST SOME VISUAL INFORMATION OF A CHROMATIC NATURE: (1) THREE TYPES OF PHOTOPIC VISUAL PHOTOPIGMENTS, EACH CONTAINED MORE OR LESS EXCULSIVELY WITHIN A GIVEN TYPE OF RECEPTOR, (2) AN ORGANIZATION OF THE RECEPTOR TYPES SUCH THAT AN OPPONENT INTERACTION OCCURS BETWEEN THE OUTPUTS OF SELECTIVE RECEPTOR TYPES, AND (3) THE CONVERSION OF THESE INTERMEDIATE DIFFERENCE SIGNALS INTO A NEURAL MESSAGE ENCODED IN TERMS OF A MODULATION OF A RESTING LEVEL OF ACTIVITY DEPENDING UPON THE BALANCE OF THE OPPONENT ACTIVITY BETWEEN RECEPTORS. IT HAS BEEN OBSERVED THAT SOME UNITS EXHIBIT A RESPONSE WHOSE ELECTRICAL SIGN DOES NOT CHANGE WITH WAVELENGTHS. THE SUBSTITUTION OF ONE WAVELENGTH FOR ANOTHER, CALLED SILENT SUBSTITUTION, IS ONE OF SEVERAL METHODS THAT MAY BE USED TO SHOW WHETHER A GIVEN SYSTEM IS MEDIATING CHROMATIC OR ACHROMATIC INFORMATION. IF BRIGHTNESS IS MEDIATED BY A UNITARY SYSTEM, THEN LUMINANCES OF LIGHTS OF DIFFERENT COLOR SHOULD BE ADDITIVE ACCORDING TO ABNEY'S LAW. NO EXPERIMENTAL EVIDENCE YET EXISTS ON THE PATTERN OF ACTIVITY IN THE BRAIN WHICH DIFFERS WHEN ONE SEES A RED VERSUS A GREEN OF EQUAL BRIGHTNESS.

  • Supplemental Notes:
    • Vol 6, No 5, PP 43-48, 18 REF
  • Authors:
    • Boynton, R M
  • Publication Date: 1968-9

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Filing Info

  • Accession Number: 00216797
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Aug 12 1970 12:00AM