cs781 - Colour for Computer Graphics - Winter 2012
Course Notes
Lecture 10 - Visual Response to Light I
And Now from our Sponsor
- Assignment 1
- Called assignment 2 in w09.
- Magnifying glasses
- Projects
Retinal Processing
The retina consists of three layers of cells
- Photoreceptors
- Bipolar & Horizontal
- Retinal ganglion
Most of what we know
Generic neuron
Cell body
Where all the work is done.
- creation of proteins
- conversion of sugar or fat to ATP
- products diffuse out of the body into the axon and dendtites
Axon
- extension of the cell that can be quite long
- long ones are wrapped in myellin to speed conduction
- roughly, animals with spines have myellin
- conducts an electric voltage away from the cell body
- as a train of spikes or as a graded potential
- myellin plus spikes move fast in a narrow axon
- At its end it synapses onto one or more dendtites
Dendrite
- many dendrites, branched like roots, come into the cell body
- signals received as voltage, from axons at synapses
- voltage conducted along dendrites to cell bodies, adding at
junctions
- voltage on cell body may or may not trigger acticity on the cell's
axon
Synapses
- axon pushes vesicles full of neurotransmitter into intercellular
space
- dendrites receive individual neurotransmitter molecules at
receptors
- cascade of chemical processes, very simmilar to the cascade in
photorectors, amplifies the signal
- poorly understood mechanisms modulate the strength, how much
neurotransmitter, how many receptors, of a synapse.
- neurotransmitter is recycled
Retinal neurons
Photoreceptors
Bipolar cells
Receive input from more than one cell type
Horizontal cells
Ganglion cells
The signals transmitted by ganglion cells is significantly processed
Adaptation
Spatial opponent organization
Colour opponent organization
- difference of red & green cones
- difference of blue and red+green
- sum of red and green also common
- rods may play a role
Psychophysics of Opponent Colours
- Reddish-green and yellowish-blue
- Unique hues
- yellow, red, blue: simple
- green: bimodal
- Flicker photometry
- luminance channel
- red-green channel
- yellow-blue channel
- Minimally distinct border
- Colour naming
- Unusual properties of yellow-blue axis
Neural Theories
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