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class+10+lecture_posted (1) - Sensation and Perception...

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Sensation and Perception Class X: Color Vision (cont.) and Space Perception
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The nervous system extracts color information by comparing the outputs of the different sets of cones. The difference between L- and M-cones provides a lot of information about how relatively “red” the image is a.k.a. “L-M” The sum of L and M gives a good measure of overall light intensity (S-cones don’t seem to play much role) a.k.a. “L+M” The difference between L+M and S gives a good measure of how relatively “blue” the image is a.k.a. “(L+M) – S)”
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Figure 5.4 The two wavelengths that produce the same response from one type of cone (M), produce different patterns of responses across the three types of cones (S, M, and L)
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Opponent Processes Lateral geniculate nucleus (LGN) has cells that are maximally stimulated by spots of light Visual pathway stops in LGN on the way from retina to visual cortex LGN cells have receptive fields with center–surround organization Color-opponent cell: A neuron whose output is based on a difference between sets of cones In LGN there are color-opponent cells with center–surround organization This occurs in some retinal ganglion cells too! Comparisons between cone outputs start early in the visual system.
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Opponent Processes There is a theory of color perception called “opponent color theory” that may or may not be related to the color- opponent processing in the LGN. Your book explains it poorly. You will NOT be tested on it.
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Opponent Processes Color processing continues in visual cortex But we don’t really understand the details yet. Achromatopsia : An inability to perceive colors that is caused by damage to the central nervous system
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Des Everyone See Colors the Same Way? Does everyone see colors the same way?— Yes General agreement on colors Some variation due to age (lens turns yellow)
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Does Everyone See Colors the Same Way? Does everyone see colors the same way?— No About 8% of male population, 0.5% of female population has some form of color vision deficiency: Color blindness
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Does Everyone See Colors the Same Way? Several types of color-blind people: Deuteranope : Due to absence of M-cones Protanope : Due to absence of L-cones Tritanope : Due to absence of S-cones
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Does Everyone See Colors the Same Way? Several types of color-blind people: (cont’d)
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class+10+lecture_posted (1) - Sensation and Perception...

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