13. theories of color vision, anatomy Flashcards
What are the 2 (original) theories of color vision?
- Trichromatic Theory (Young-Helmholtz, 1802/52)
- Opponent Process Theory (Hering, 1878)
Modern color vision theory?
- combination –> its a 2-stage process
1. trichromatic color representation
2.opponent color representation
Trichromatic theory explanation?
- 3 kinds of cone receptors w/ diff. spectral SENSITIVITIES
- each wavelength = unique pattern of activation in cones
- color is based on relative amount of activity in 3 mechanisms
Spectral sensitivity (function) def?
- these are the graphs that show what wavelengths the S, M, & L cones are most sensitive to
- RELATIVE sensitivity (as a function of) different WAVELENGTHS
- PROBABILITY that a cone’s photopigment will absorb a photon of light of any given wavelength.
How is trichromatic theory represented on a spectral sensitivity graph?
- each wavelength corresponds to one unique pattern of activity in the cones
- for any wavelength, if you draw a line up, it shows you the percentages of activity for each R, G, & B
Ex. - 540nm –> 1%B, 100%G, and 85%R
Principle of univariance meaning?
absorption of a photon of light results in the same response regardless of the wavelength of the light.
Why do we need more than one type of cone?
- principle of univariance –> response depends only on intensity (more photons)
- many wavelengths could produce the same response with varied intensity
- with at least 2 cone types, you can distinguish most colors
How did Young and Helmholtz figure out that there are 3 types of cones? (experiment)
- metameric color matching experiment
- provided monochromatic color patch
- asked to combine lights to match that color
- they could re-create any color using diff. intensities of R,G,B
Metamer def?
Any two stimuli that are physically different but are perceived as identical.
4 problems Hering found with Trichromatic theory?
- people create 4 groups (RGYB)
- No one perceives yellowish blues or reddish greens
- Simultaneous contrast
- Afterimages
–> both 3&4 reveal pairs of colors
–> R/G & Y/B
Opponent process theory explanation? What type of experiment did he do?
- we perceive 2 intrinsic color pairs
–> R/G & Y/B - all you need to know to define a color is how much Y/B and how much R/G
- Hue cancellation
–> measures relative strengths of color pairs
How is opponent process theory represented on a graph?
- cancellation experiments show the strengths of each color throughout the spectrum
- if you align the R/G graph under the Y/B graph, you can draw a line at any wavelength to see…
- How much Y/B and how much R/G
- this will tell you the color
Opponent process theory and lateral inhibition??
For Yellow/Blue:
- excitatory response from S cones means there’s lat. inhib. from M&L cones
–> +S–ML
–> +B–Y response
- excitatory response from M&L cones, means there’s lat. inhib. from S cones
–> +ML–S
–> +Y–B response
For Red/Green:
- excitatory response from M = lat. inhib. from L
–> +G–R response
- excitatory response from L = lat. inhib. from M
–> +R–G response
Single opponent neurons provide information about…?
Uniform color / illumination
Double opponent neurons provide information about…?
Red / green edges in the receptive field
