Week 4 Flashcards
Trichromatic Theory of color vision
Suggested that three different receptor mechanisms are responsible for color vision
metamers
two different stimuli that give observer the same experience of color
Experiemnt suggesting observer needs 3 wavelengths of light to match the color
Color-matching exp by Maxwell
Observer with color deficiencies need how many?
2
Problem with Trich Theory
Blindness occurs in pairs of green/red and blue/yellow.
Individuals then have trouble visualizing combos of red/green or blue/yellow.
Color afterimages show exhaustion of one color (green) produces another color (red)
Opponent-process theory
(Ewald Herring)
Suggests three mechanisms process colors in pairs r/g b/y and black/white.
They respond opposing fashion: + to red and - to green.
(lose one, lose color vision for both colors)
Single-cell recordings
In 1950s found opponent cells which are located in the retina, LGN (parvocellular and koniocellular layers), and in the cortex.
Opponent cells
Responded in an excitatory manner to one
range of wavelength and inhibitory to another.
This supported opponent-process theory except the black-off white-on was not apparent in color vision.
Recall selective adaptation where neurons selective for specific stimuli get fatigued when exposed for a long time. For opponent cells, if we are exposed to blue for a long time then blue-on and yellow-off will be fatigued. If we were then shown a white screen we should get a release from inhibition (where the cell inhibited starts to fire more), what color should we see?
a. Red
b. Yellow
c. Blue
d. Green
e. Rainbow 🌈🦄
bruh they didn’t give the answer but yellow?
How are he physiological mechanisms underlying the trichromatic and opponent process theories of color are compatible?
- Trichromatic theory explains the responses of the cones in the retina.
- Opponent-process theory explains neural response for cells with those cones in their receptive fields. These signals affect activity in retina, LGN and cortex.
There is __ single module for color perception
no
Inferior temporal lobe
involved with object recognition (patients with visual agnosia)
Parietal lobe
involved with spatial relationships (difficulty with remembering landmark)
Dorsal pathway
Where/How
Ventral pathway
What
Dorsal and ventral pathway
- Originated in retina and continue through ganglion cells in the LGN
- Have some interconnections
- Receive feedback from higher brain areas
Short wavelengths
419-nm, S-cone
Medium wavelengths
531-nm, M-cone
Long wavelengths
558-nm, L cone
Ablation studies
what areas of the brain are associated with specific behaviors:
- First, an animal was trained on perceptual capacities and then measure their behavior.
- Second, a specific part of the brain was removed or destroyed (ablated).
- Finally, test the animal again to see if their behavioral results change.
Object discrimination problem
- Removal of inferior temporal lobe tissue, resulted in problems with the object
discrimination task - “What pathway” in brain because it is critical for target identification
Landmark discrimination problem
- Removal of parietal lobe tissue, resulted in problems with the landmark discrimination task.
- “Where pathway” in brain because it is critical for spatial relationship
Sensory Codes:
Specificity
Distributed: Sparse, Population
Specificity code
have a single neuron represent each object
Distributed coding
have many groups of neurons represent each object
Sparse coding
fewer groups are needed for representation (but always more than a single)
Population coding
more groups of neurons in representation
Domain Specificity models
- Certain brain regions are dedicated to specific categories of objects [e.g. faces]
- More modularity(particular), less plasticity (can be retrained)
- Generally expect to find sparse codes
Property-based models
- Object knowledge is linked to sensory and motor attributes
- Constructivist/ embodied cognition view - less modularity, more plasticity
- Generally expect to find population codes
double dissociation
two functions involve different brain mechanisms and operate independently
damage to FFA can cause
prosopagnosia
