Colour, depth and motion Flashcards
What is colour vision used for
frugivory (eating fruit)
sexual signalling
social signalling (embarrassment)
Trichromats vs dichromats
tri- 3 cones
di- 2 cones
what is colour
produced by visible electromagnetic radiation
different wavelengths associated with different colours
Trichromatic theory
matching experiment with normal vision. Required at least three wavelengths to make colour matches
our perception of colour occurs from spectral sensitivity of three detectors
Physiological evidence for Trichromatic theory
3 different types of cones which respond to different wavelengths.
Opponent processing
Colour aftereffects and colour-blindness not explained by tri
instead two colour units red-green and blue-yellow plus a monochrome one light-dark.
Which colour theory is correct
both
initial processing is tri
in LGN opponent processes
Where does yellow come from
medium and short waves
Why is depth perception important
grasping
know where things are
the four fs
Convergence/divergence
angle of eye changes to fixate
knowledge of where eye pointing to tell depth
Focus/accomidation
feedback from muscles
weakness of convergence and accommodation
x- only give depth about 1 item
reasons for two eyes
overlapping visual fields to have depth
Panoramic vision allow for huge field of vision acts early warning system
encoding depth with two eyes
compare the two different images of the eyes known as binocular disparity
depth perception due to this known as stereopsis
where does depth perception coding occur with two eyes
left and right pathways separate so must occur at least v1
cells driven by binocular input in v1 signal disparity but don’t perceive depth so occurs higher up in v2
issues with using stereopsis
if remove other cues then limited in its utility
only useful for stuff within arms reach
lots of populate don’t have this ability well so cant be that important
Other reasons to have two eyes
more sensitive
spare eye
see through things
an epiphenomenon of bilateral symmetry
Occlusion
monocular depth cue
one thing in front of the other means its closer
Linear perspective: texture gradient
monocular depth cue- finer details gets worse the further away it is
Linear perspective: height in image
monocular depth cue - closer it is to horizon the further away it is
linear perspective: linear convergence
monocular depth cue- parallel lines look nearer is further away
size constancy
monocular depth cue- know size of objects so if appear bigger then must be closer.
fMRI evidence for it happening in v1
Velocity gradients
monocular depth cue- things closer move quicker (motion parallax)
Aerial perspective
monocular depth cue- stuff far away appears bluer
