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PSY 280 L11.14

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University of Toronto St. George
Matthias Niemeier

PSY 280 – P ERCEPTION M. N EIMEIER 11/14/12 THE PERCEPTION OFCOLOUR AND M OTION SA: Describe one experiment that would suggest that faces aren’t special. What were participants asked to do? Which method was used? What was found? What does that potentially mean? - Visual specialization - Train and acquire visual expertise regarding one category/kind of objects - Greebles, fMRI - Brain activation in FFA – activated in specialization - FFA not just for faces – emotional component - FFA involved with any visual expertise **C H. 2, 3, 4, AND SOME OF 8 FOR THE 2 M IDTERM Colour - Univariance a problem - Colour not a physical property – psychophysical o Most light is reflected – broad spectrum of wavelengths o 400-700 nm – eyes can see - Bitmap – superimposition of Green, Red, Blue layers - Univariance – different wavelength intensity combinations can elicit exactly some response from a single type of photoreceptor o Cannot make colour discrimination based on wavelength (single photoreceptor) - Only the response of receptor will tell us something about light we’re looking at o Output of one cone is completely ambiguous - Curve, output of receptor - line of curve that passes through output line = colour of light (wavelength) – same luminance – ambiguous because could be Blue or Orange though most receptive to Green Cone photoreceptors - S cones – short wavelengths (blue) – 440 nm - M cones – medium wavelengths (green) – 535 nm - L cones – long wavelengths (red) – 565 nm - Scotopic – based on rods – low level of light – cones not so responsive o Photopigment molecule – Rhodopsin o Same sensitivity to wavelength, impossible to discriminate light o All grey - Cones see green but broad curve - Newton and prisms - Young-Hemholtz (-Maxwell) theory: trichromatic colour vision o Based on three photoreceptors sensitive to particular ranges of wavelengths - Color matching technique – combination of R, B, G – different intensity of wavelengths to create similar bluish light (for example) - Color created by mind - 3 cone types = tell difference between lights of different wavelengths o Bell curve response - Seldom see one wavelength at a time o Cooked and raw meat reflect sunlight in different wavelengths - Red and Green light mixed together in right proportion will stimulate L and M cones the same as yellow light o Can't distinguish - Metameres – pair of stimuli perceived as identical in spite of physical differences o Different mixtures of wavelengths that look identical (in terms of light) - Elude to the imitation of colour perception - Additive colour mixture – mixture of lights o A + B reflected from a surface to eye, effects of those 2 lights add together o Mixing lights with different colours - Subtractive colour mixture – mixture of pigments o A + B pigments mix, some of the light shining on the surface will be subtracted by A, some by B o Remainder contributes to the perception of colour  Surface looks blue because it absorbs long (R) wavelengths and medium (G) wavelengths - Colour space is 3D – 3 cones - Hues: chromatic aspect of color - Saturation: chromatic strength of a hue - Brightness: distance from Black in colour space - 3 dimensions independent of one another - Non-spectral hue – hues that doesn’t exist as pure forms of light but onle as a mixture of different wavelengths o 420 and 680 nm stimulates L/S cones but not M cones - Herring’s idea – illegal colours o E.g., reddish green - Opponent colour theory – perception of colour based on output of 3 mechanisms, each of them on an opponency because 2 colours o Red-Green, Blue-Yellow, Black- White - Psychophysical support for the Opponent Colour Theory ~ o Afterimage: visual image seen after stimulus has been removed - Neurophysiological support: o LGN has colour opponent cells – neurons whose output based on difference between sets of cones o Cells integrating colour information (?)  Based on cones - Colour system in V1 - blobs o In V2 thin stripes – colour columns - Human V4 – ‘colour’ area o Specialized for colour perception - Achromatopsia – inability to perceive colours due to damage to central nervous system (lesion in V4) - Does everyone see colours the same way? - Yes: o General agreement on colours o Same metameres o Same variation due to age (lens turn yellow) - No: o About 8% of males and 0.5% of females have some form of colour vision deficiency – colour blindness o Ishihara test o Two types of colour blind people  Cone monochromat – only one cone type; truly colour blind  Rod monochromat – no cones of any type; truly colour blind, badly visually impaired in bright light o 3 types of colour-anomalous people:  Deuteranope – no M cones  Protanope – no L cones  Tritanope – no S cones - Maybe: o Cultures / languages describe colours differently  English: 11 colour terms (strict definition)  Other languages have different numbers, e.g., 2/3 o Idea of cultural relativism - Unrelated colour – a colour that can be expressed in isolation - Related colour – a colour, such as brown/grey that is seen only in relation to other colours - Brown really orange light – depending on context - Ability to preserve colours in whatever context/situation as the same o Colour constancy – based on reflectance - Tendency of a surface to appear the same colour under a fairly wide range of illuminatio
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