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1、Color VisionBy Andrew J PakchoianPsych 159 Prof MacleodRoad MapPigment anatomyPhotoreceptor anatomyNeurobiology of color visionPhysiology of color blindnessKey TermsMC layer magnocellularPC layer parvocellularLGN lateral geniculate nucleusPigment Anatomy3 types of cones: short (S), middle (M), and l

2、ong (L) wavelength sensitive.(S): 430 nm = blue(M): 530 nm = green(L): 560 nm = redPigment AnatomyOrigin of pigmentsRed/green from opsin gene on X-chromosome or sex chromosome.Show very similar amino acid seqs. (96%)Blue on chromosome 7 and rhodopsin on chromosome 3 are very different.Photoreceptor

3、AnatomyCones more concentrated near foveaAdapts to a wide range of illumination colors and levels.Rods spread throughout the retinaProvide quick response to changes in illumination.Photoreceptor AnatomyMeasuring Wavelengths:Short wavelengths causes the green receptor to fire.As the wavelength gets l

4、onger and closer to 580 nm the red begins to fire, surpassing the green.Get mix of wavelengths.Therefore, color vision is the consequence of unequal stimulation of the 3 types of cones. In a specific ratio.Photoreceptor AnatomyExample: if you stimulate all 3 types of cones about equally the result i

5、s white or no color. Neurobiology of color visionOnce again 3 types of cones: S, M, and L.Only 2 types of horizontal cells: H1 which connects L and M cells.H2 which connects S with some L and M cells.The relation between high specificity of cone connectivity and chromatic processing is unclear.Neuro

6、biology of color visionBlue/Yellow Pathway:2 Systems:Differentiate signal from S 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.Conclusion: The ganglion cells : Small bistratified

7、 cell and small bodied inner cell form blue/yellow pathway.Neurobiology of color visionRed/Green Pathway:Differentiate between signals from the L and M cones.Path: Single L and M cones receive input connect to single midget bipolar cells contact single midget ganglion cells project to the PC layer o

8、f LGN.Neurobiology of color visionRed/Green Pathway Contd:L and M cones have two forms: ON and OFF-centreON-center midget cells for L and M have identical arrays and same with the OFF-centerThere is no overlap between dendritic trees of central midget ganglion cells which leads to the exact 1:1 rati

9、o 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 visionInteresting facts:In the periphery of the retina chromatic sensitivity drastically decreases, but responsiven

10、ess of PC cells is unchanged Connectivity to midget bipolar cells is not random. Physiology of color blindnessMale dominant trait but females 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

11、.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

12、colors.Physiology of color blindnessA few types:Anomalous Trichromacy: have 3 photopigments, but only from 2 groups.Most common is deuteranomalous = 2 L photopigments. Dichromacy: missing 1 group of photopigments.Which picture contains a red crayon?ExampleQuizTrue or false: The dendritic trees of mi

13、dget ganglion cells overlap.AnswerFalseReferencesColorblindness: ://newman/courses/bio22298/disorderpapers/Colorblindness/preliminary.htmHubel, David H. Eye, Brain, and Vision. Harvard Medical School. 15 Jan.2005Lee, Barry B. Paths to Colour in the Retina. Rev. of Current understandingof neurobiology of color vision. Clinical and Experimental Optometry20 June 2004: 239-248.Levine, Michael W. Fundamentals of Sensation and Perception. 3rd ed. NewYork: Oxford, 2000. 94-110.Neitz, Jay ,