Color Vision By Andrew J Pakchoian Psych 159 Prof Macleod Road Map вЂў Pigment anatomy вЂў Photoreceptor anatomy вЂў Neurobiology of color vision вЂў Physiology of color blindness Key Terms вЂў MC layer magnocellular вЂў PC layer parvocellular вЂў LGN lateral geniculate nucleus Pigment Anatomy вЂў 3 types of cones: вЂў вЂў вЂў short (S), middle (M), and long (L) wavelength sensitive. (S): 430 nm = blue (M): 530 nm = green (L): 560 nm = red Pigment Anatomy вЂў Origin of pigments вЂ“ Red/green from opsin gene on X-chromosome or sex chromosome. вЂ“ Show very similar amino acid seqs. (96%) вЂ“ Blue on chromosome 7 and rhodopsin on chromosome 3 are very different. Photoreceptor Anatomy вЂў Cones more concentrated near fovea вЂ“ Adapts to a wide range of illumination colors and levels. вЂў Rods spread throughout the retina вЂ“ Provide quick response to changes in illumination. Photoreceptor Anatomy вЂў Measuring Wavelengths: вЂ“ Short wavelengths causes the green receptor to fire. вЂ“ As the wavelength gets longer and closer to 580 nm the red begins to fire, surpassing the green. вЂ“ Get mix of wavelengths. вЂў Therefore, color vision is the consequence of unequal stimulation of the 3 types of cones. In a specific ratio. Photoreceptor Anatomy вЂў Example: if you stimulate all 3 types of cones about equally the result is white or no color. Neurobiology of color vision вЂў Once again 3 types of cones: S, M, and L. вЂў Only 2 types of horizontal cells: вЂ“ H1 which connects L and M cells. вЂ“ H2 which connects S with some L and M cells. вЂў The relation between high specificity of cone connectivity and chromatic processing is unclear. Neurobiology of color vision вЂў Blue/Yellow Pathway: вЂ“ 2 Systems: вЂў Differentiate signal from S вЂў вЂў вЂў and the summed signal from L and M. = +S-(L+M) Receives input from S-cone bipolars (ON) and L and M cone bipolars (OFF) Second system = -S+(L+M) Input signals are unclear. вЂ“ Conclusion: The ganglion cells : Small bistratified cell and small bodied inner cell form blue/yellow pathway. Neurobiology of color vision вЂў Red/Green Pathway: вЂ“ Differentiate between signals from the L and M cones. вЂ“ Path: Single L and M cones receive input connect to single midget bipolar cells contact single midget ganglion cells project to the PC layer of LGN. Neurobiology of color vision вЂў Red/Green Pathway ContвЂ™d: вЂў L and M cones have two forms: ON вЂў вЂў вЂў and OFF-centre ON-center midget cells for L and M have identical arrays and same with the OFF-center There is no overlap between dendritic trees of central midget ganglion cells which leads to the exact 1:1 ratio of cones to ganglion cells. More than 10 to 15 degrees in the periphery we do find some overlap of dendritic trees in the midget bipolar cells, but not ganglion. Neurobiology of color vision вЂў Interesting facts: вЂ“ In the periphery of the retina chromatic sensitivity drastically decreases, but responsiveness of PC cells is unchanged Connectivity to midget bipolar cells is not random. Physiology of color blindness вЂў Male dominant trait but females вЂў вЂў вЂў вЂў вЂў вЂў carry it. Females have 2 X chromosomes so trait is normally not expressed. Males have 1 X and 1 Y chromosome which means recessive traits will show in phenotype. As stated before, red and green pigments originate on the X chromosome. 1 in 20 males suffers from some form of color blindness. Most common is red-green color blindness which is caused by problem with M or L cones. However, they can still see red and green, but have trouble with light or desaturated colors. Physiology of color blindness вЂў A few types: вЂ“ Anomalous Trichromacy: have 3 photopigments, but only from 2 groups. вЂў Most common is deuteranomalous = 2 L photopigments. вЂ“ Dichromacy: missing 1 group of photopigments. Which picture contains a red crayon? Example Quiz True or false: The dendritic trees of midget ganglion cells overlap. Answer False References вЂў Colorblindness: вЂў вЂў вЂў вЂў вЂў http://srv2.lycoming.edu/~newman/courses/bio22298/disorderpapers/Colorbli ndness/preliminary.htm Hubel, David H. Eye, Brain, and Vision. Harvard Medical School. 15 Jan. 2005 Lee, Barry B. "Paths to Colour in the Retina." Rev. of Current understanding of neurobiology of color vision. Clinical and Experimental Optometry 20 June 2004: 239-248. Levine, Michael W. Fundamentals of Sensation and Perception. 3rd ed. New York: Oxford, 2000. 94-110. Neitz, Jay , and Maureen Neitz. Neitz Color Vision Lab. 21 Feb. 2002. Dept. of Opthamology, Medical College of Wisconsin. 14 Jan. 2005. Scott, Ed. Spectral Selectivity. 1997. Luminal Path Corporation and contributors. 15 Jan. 2005.