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Lecture 15

PSYC 101 Lecture Notes - Lecture 15: Gross Anatomy, Color Vision, Trichromacy

Course Code
PSYC 101
Luke Clark

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how does the eye work? retina, fovea, lens
visual transduction: photoreceptors (rods and cones), colour vision
the visual field: neural receptive fields and topographic organization of
visual cortex
fovea contains rods and cones
rods — black and white
cones — colour
receptive fields: bipolar and retinal ganglion cells act to summarize
information from a patch of photoreceptors
this retinotopic organization is retained when the signals reach the
retinal ganglion cells (1 million)
colour vision
trichromatic theory
red, green and blue cones
balance of firing across 3 cone types yields the colour
(pattern coding)
color opponent theory
some colours work against others
colour after-images
opponent-process theory test
opponent process theory is a psychological and
neurological model that accounts for a wide range of
behaviours, including colour vision.
ability to perceive color is controlled by three receptor
complexes with opposing actions
red-green, blue-yellow, black-white
can only detect the presence of one color at a time because
the two color oppose one another
colour opponency
red light stimulates ‘red’ cone —> excites ganglion cells —>
signals red
green light stimulates ‘green’ cone —> inhibits ganglion
cells —> signals green
yellow light stimulates ‘yellow’ cone —> excites ganglion
cells —> signals yellow
excitation and inhibition cancel each other; no other
charge in signal
as information leaves the eye...
visual fields
connection to the thalamus
LGN of the thalamus
optic chiasm
nasal fields cross here
connection to the occipital lobe
primary visual cortex (V1)
cortical processing of the visual field
damage to primary visual cortex (V1) leads to partial blindness
(=scotoma) or full cortical blindness
restinotopic organization of visual cortex
Hubel & Wiesel: ElectROphysiology
single-neuron feature detectORS
AREA V1 contains neutrons that respond to specific orientations of
colour and motion
there are specialised regions in visual cortex for processing colour
(V4) and motion (MT, or V5)
cerebral achromatopsia
damage to V4
damage to V5/MT