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Lecture 3

PSYCH 1XX3 Lecture Notes - Lecture 3: Visual Cortex, Color Blindness

Course Code
Joe Kim

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Ability to see colour is not because the objects are inherently colourful
Objects and surfaces reect certain wavelengths of the visible spectrum
Reected wavelengths trigger specic patterns of responses in our brains
that give rise to our  experience of colour
 
Bulls do not see a cape as red, but as a piece of grey moving cloth
More likely responding to motion
Many birds, sh, reptiles and insects have excellent colour vision
Mammals: Colour vision is limited to primates
%  colour vision’s well suited to distinguishing red and yellow against
a green background
oAdaptation helps with foraging for fruit in bushes and trees
oDetecting predators or prey against a background, determining
ripeness of fruit, richness of the soil or using the colour of sunsets as a
means to predict weather
Birds, sh and insects are able to see colours we don’t see at all (UV end)
 &
oColour of potential mates feathers, signals how healthy that bird is
oBird that looks ordinarily coloured to humans may look particularly
brightly coloured to other birds
oCommunicate about how sexy and
healthy they are, while remaining
inconspicuous in the forest to potential
 &
oSome owers have adapted patterns on
the petals that are invisible to us,
serving as “nectar maps”
Few colour receptor types activity combine in various proportions to make
every colour
% : Three colours that can be combined in various proportions
to make every colour in the spectrum
o“basic colour” – cannot be reduced into other colours
oNo colours that can be mixed together to form a primary colour
$ ()*: When coloured pigments
 
%+ * ,

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oAll wavelengths absorbed
those that two pigments 
o% -%%  =
.()*: When coloured
% + * to
the mixture
oOur visual system adds the e3ects of
di3erent wavelengths together in our
nervous system
oPrimary colours /* and 
because they can be added in various
proportions to make all the di3erent
colours we see
oComplementary colours are also di3erent
o% -%%  = * or+
oSeen in TV screens, composed of tiny dots that are either red, blue or
1% 1: Retina contains
three di3erent kinds of cones, each
maximally sensitive to di3erent
wavelengths of light
oFirst proposed by
Thomas Young
oModied by
o“Young-Helmholtz theory” or
theory of trichromatic colour
* 1
oFits with additive colour mixing
oPhysiological evidence for three types of cones
 %+1
oYellow seemed to be a primary colour and not a mixture of red and
oCouldn’t explain the  +%% 
Certain pairs of wavelengths produces the experience of white
o%%  % *why do you see a yellow
afterimage when you stare at a blue stimulus?
(1920) – three classes of receptors, but each of these receptors are
%   
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