Lecture 6 - 26.01.11

Lecture 6 - 26.01.11 - 26th January 2011 Psych 120B Lecture...

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26 th January 2011 Psych 120B – Lecture 6 Perceiving Colour V. Theories of Colour Vision Address how basic mechanisms relate to colour experiences Both theories were proposed in the 1800s based on behavioural data. Physiological data (discussed earlier and later) supporting them did not become available until 70 years later! Colour Matching Experiment Presented different light rays on the test field and on the other side, the subject was allowed to play with three knobs that controlled the intensities of three different wavelengths (on the comparison field). Task was to turn the knobs until the comparison field matched the test field completely. Colour Matching Experiment Results By adjusting the proportions of three wavelengths it is possible to make the colour of comparison and test fields match. Need at least three wavelengths to match all wavelengths in the spectrum. The three wavelengths have to be independent (none can be matched using the other two). Trichromatic Theory (Young-Helmholtz Theory) 3 receptors 3 primary colour sensations o All other colours are complex colours made up of a combination of the other three. Blue / Green / Red o What is yellow? Claimed to be a combination of Green and Red. Three Cone Types – S M L Blue – S activated Green – M is activated Red – L is activated White: All are activated Trichromatic Theory How does the theory handle perceptual colour phenomena? Young-Helmholtz Theory Intuitions: Simple and complex colours o EXCEPT yellow Yellow does not seem to be a compound, nor does it seem to be a greenish red. Trichromatic Theory Contrast:
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o Blue/Yellow o Green/Red o Red/Green Doesn’t explain the contrast very well. According to this theory, contrast from both red and green ought to lead to blue component. Why we see other colours when we stare at one colour for a long time. Fatigue from the neuron’s firing.
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This note was uploaded on 03/07/2011 for the course PSYCH 120B taught by Professor Shams during the Winter '09 term at UCLA.

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Lecture 6 - 26.01.11 - 26th January 2011 Psych 120B Lecture...

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