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Chapter 11

Chapter 11.doc

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McGill University
PSYC 212
Remy Allard

Chapter 11The Visual System Colour PerceptionThere is no such thing as colourred does not exist the object emits long wavelength lightPhysical nature of light that entrees are eyes is responsible for producing psychological property of visual experiencenot inherent property oflightthe object itselfColour visionthe ability to differentiate lights or objects that reflect light only on the basis of their spectral composition ie Wavelength content even if the lights appear to be of equal subjective brightnessSpectralpertaining to the wavelength of light or other types of electromagnetic radiationEvolution of colour vision highly beneficial for natural selectionA Colour ScienceEncompasses studymeasurement of both physical and psychological factors that govern colour perceptionChromaticitythe quality of a colour1 The chromatic nature of lightColour is an inherent property of objectsoVery intertwined with objects formNewton discovered colour perception is generated by light itselfsunlight made up of number of discrete components that produced a different colour experienceNewtons breakthroughoFamous prism experimentoGlass prism in path of beam of sunlight through small hole in window shadepassed through white screen and rainbow colours appearedoIncident light refracted at both surfaces of the prism so that violet light is refracted the most red light the least others in various degrees in betweeno7 coloursROY G BIV red orange yellow green blue indigo violetoNewton convinced sunlight composed of different colours of light that when combined produced white lightoDidnt understand why it split into different colours but came close to realizing wavelengthsoUnderstood that the colours we perceive are not that of the light itselfthere was no colour in light but we see colour after a particular light interacts with visual systemSpectral nature of light sourcesoSunlight dissociated into continuous bands of colours by prismContains sufficient photons at all wavelengths across visible spectrum 400700 nm band of electromagnetic radiation visibleverified using device to plot energy content of sunlight at each visible wavelength and make emission spectrum a plot of energy content of a light source as a function of wavelength within the visible rangesunlight shows relatively similar numbers of photons across the full visible spectrum therefore when sunlight passes through a prism it is refracted along a gradient of wavelengthemission spectrum of sunlightcontinuous photon energy is presented at all visible wavelengthsotungsten also has a continuous spectrum but it is biased towards the higher wavelengths in terms of energy content giving ordinary household light bulbs yellowing appearanceofluorescent light bulb has few discrete spikes of energy at different wavelengths within visible spectrumolaser pointerslasers usually have only one energy spikeat 6328 nm for deep red appearanceadditive colour mixturesoneutral coloura colour that is not found within the visible spectrum but which can blend in with all of the spectral colours Colours such as white grey and black are neutral coloursoadditive coloursperceptual result of superimposing two or more such lights on eachotherodiscovered by Newtonothe addition of two different coloured lights would produce an intermediate sensation from within the rainbow of colours ocolour circlea graphical scheme that portrays the spectral colours in a circular manner discovered by Newton to join the colours togetherocolour cycle paved way for simple geometric procedures by which intermediate colours can be predicted from mixture of any two coloured lightsomixing two coloured lights of equal intensity would produce a colour that lies precisely midway between them on the colour circleodifferent colours here smoothly blend into each other rather than being depicted as discrete wedgesoif two equally intense colours are mixed ie red and green the resulting mixture will be predicted as in the middle of the twooaccurate account of the predicted colour could be made even if they were not of the same intensityocolour circle predicts perceived colour that results from mixing any pairs of lightsowhite light is when a pair of lights that are completely opposite to eachother are consideredocomplementaryany pair of colours that lie at opposite ends of the colour circle which when mixed together produce a neutral colour such as whiteoevery colour in colour circle has a complementary colourNonspectral coloursoWhite light made of series of spectral colours but is not a spectral colour itself
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