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PSYC 2390 (118)
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Chapter 9

Chapter 9 (Part 2)

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PSYC 2390
Lana Trick

Chapter 9bTritanopia Affecting only about 0002 males 0001 females Blue at short wavelengths red at long wavelengths neutral point570 nm Physiological Mechanisms of ReceptorBased Color Deficiency What are the physiological mechanisms of color deficiencyMost monochromats have no color vision have one type of cone or no conesDichromats are missing one visual pigmentoWith protanope missing the long wavelength pigment oDeuteranope missing medium wavelength pigment oTritanopes rarity because of the low number of shortwavelength cones In normal retinas difficult to determine which pigment tritanopes are missing probably missing the short wavelength pigment Genetic researchIdentified differences in genes that determine visual pigment structure in trichromatsgenes that determine visual pigment structure in trichromatsdichromats Based on research anomalous trichromats probably match colors differently from normal trichromats difficulty discriminating between some wavelengths because ML pigment spectra have been shifted closer together OpponentProcess Theory of Color Vision Ewald Hering used the results phenomenological observations which stimuli were presentedobservers described what they perceived to propose opponentprocess theory of color vision Theory states that color vision is caused by opposing responses generated by blueyellow pairingby redgreen pairing Behavioral Evidence for the Theory Hering observed that viewing a green field generates a red afterimage viewing a yellow field creates a blue afterimage Also observed the oppositegreen causes a red afterimage viewing blue causes yellow afterimage Based on observations Hering proposed redgreen pair Blueyellow pair Herings observationpeople who are colorblind to red are also colorblind to green people who cant see blue also cant see yellowLed to conclusion that redgreen are pairedthat blueyellow are paired The Theory Vision Is an Opponent Process Herings theory proposed three mechanisms each of which responds in opposite ways to different intensities or wavelengths of light BlackWhitemechanism responds positively to white light negatively to the absence of light RedGreenresponds positively to red negatively to greenBlueYellowresponds negatively to bluepositively to yellow The Physiology of OpponentProcess Vision Measured the response of single neurons to different wavelengthsProvided physiological evidence of neurons that respond in opposite ways to blueyellowto redgreen Opponent Neurons In retina lateral geniculate nucleus responded with excitatory response Light one part of the spectrum with inhibitory response to light another Notice firing decreases to below the level of spontaneous activity Neuron is called a B Y neuron because wavelengths that cause increase in firing
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