2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 20021 Psychophysics of colour perception Neurophysiology, psychophysics, and magic (or you only.

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Presentation transcript:

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Psychophysics of colour perception Neurophysiology, psychophysics, and magic (or you only though you knew what colour was…)

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Why have colour vision? Why don’t other mammals have colour vision? Why do bees have colour vision? Is hue or luminance more useful? Is hue or luminance more accurate?

2002/02/05PSYC , Term 2, Copyright Jason Harrison, The neurophysiology of colour vision Rods and cones –Rods are inhibited during day light –Cones are “blind” during night light Three different types of cones, each optimally responsive to a different wavelength 1.L-Cone: long wavelength, red 2.M-Cone: medium wavelength, green 3.S-Cone: short wavelength, blue Each type responds to a range of wavelengths

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Cone wavelength ranges SML Wavelength (nm) Relative absorption

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Cone Distributions Where is the fovea? Why is blue a “bad” colour?

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Young-Helmholtz theory of colour 3 primaries needed to produce any spectral colour 3 cones found in the retina simplest colour vision theory: –cones transduce light and send signals directly to brain

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Weaknesses of the YH colour theory red-green are mutually exclusive (opponency): –a red light can have a blue or yellow tint but not a green tint –a green light can have a blue or yellow tint but not a red tint purple orangebrown cyanyellow-greenbrown

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Weaknesses of the YH colour theory blue-yellow are mutually exclusive (opponency): –a blue light can have a red or green tint but not a yellow tint –a yellow light can have a red or green tint but not a blue tint purple orangegrey cyan yellow-green grey

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Patching up the YH colour theory Hering theorized opponent channels –one type of colour receptor –three colour channels: Red/Green, Yellow/Blue, White/Black –also explains coloured afterimages –does not explain colour matching (requires 3 types of colour receptor) Modern opponent process theory: –combine Young-Helmholtz and Hering

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Modern opponent process theory different combinations of three cone types are fed into the channels: –achromatic: M+L cone responses –blue-yellow: M+L versus S cone responses –red-green: L+S versus M cone responses chromatic channels are weighted so that they give a zero response to white

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Colour opponent channels achromatic: –M+L cone blue-yellow: –M+L versus S cone red-green: – L+S versus M cone SML Relative efficiency

2002/02/05PSYC , Term 2, Copyright Jason Harrison, What is colour? Property of objects? Property of light? Property of our brain?

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Physical dimension e.g. wavelength Psychological dimension e.g. colour ? Psychophysics of colour

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Colour experiments determine number of distinguishable colours –JNDs determine number of “necessary colours” organize the colours according to similarity

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Colour similarity resulting ordering seems to be cyclic where should white and black go? where is purple?

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Colour similarity white and black correspond to saturation and brightness

2002/02/05PSYC , Term 2, Copyright Jason Harrison, HSV: Hue, Saturation and Value Hue: spectral hues + mixed colours like purple Saturation: purity of colour Value: brightness or intensity purple!

2002/02/05PSYC , Term 2, Copyright Jason Harrison, high low high low HSV: Hue, Saturation and Value Hue SaturationValue

2002/02/05PSYC , Term 2, Copyright Jason Harrison, hue HSV: a psychological colour space

2002/02/05PSYC , Term 2, Copyright Jason Harrison, saturation HSV: a psychological colour space

2002/02/05PSYC , Term 2, Copyright Jason Harrison, low high brightness medium HSV: a psychological colour space

2002/02/05PSYC , Term 2, Copyright Jason Harrison, white black HSV: a psychological colour space

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Brightness high medium low high medium low white black

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Brightness high medium low high medium low white black

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Brightness high medium low high medium low white black

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Brightness high medium low high medium low white black

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Brightness high medium low high medium low white black

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Colour constancy Discounting the spectral distribution of the light source –Incandescent lights are reddish –Sun is yellowish –Sun setting is orange Similar to lightness constancy

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Colour constancy demo

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Colour constancy demo

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Colour constancy demo

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Congenital colour deficiency Approximately 8% of the population (1 in 12) Sex linked genes on X-chromosome –mostly men (women possibly tetrachromats) Three types: missing or abnormal 1.protanopia/protoanomaly: L-cones 2.deuteranopia/deuteranomaly: M-cones 3.tritanopia: missing S-cones SML

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Colour vision tests

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Colour vision tests

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Normal colour vision

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Protanopia L-cone, red/green deficient

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Deuteranopia M-cone, red/green deficient

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Tritanopia: S-cone, blue/yellow deficient

2002/02/05PSYC , Term 2, Copyright Jason Harrison, NormalTritanopia DeuteranopiaProtanopia Comparison

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Bilateral damage to V4 results in achromatopsia “she looked like a rat”, Rama p. 73 Neurons in V4 respond to colours (not wavelengths) Cerebral Achromatopsia

2002/02/05PSYC , Term 2, Copyright Jason Harrison, Benham, Fechner disks Black and white patterns that produce colours –flickering monochromatic light below 40Hz Colour is sensation NOT just physics Does colour exist “out there”? Or “up here”?