Color perception Flashcards
Opsin
Part of pigment that is sensitive to wavelength
S, M and L-cones
S-cones : have opsins that absorb short wavelengths
M-cones : medium wavelengths
L cones : longer wavelengths
Qualia
Subjective, first-person experiences of perception and sensation that are inherently personal and difficult to communicate or measure objectively.
Mary’s room thought experiment
If Mary knows everything about color, but has never seen it, does Mary learn something new when she experiences color for the first time?
- If she does, it means there is more to knowing about color than just the physical facts—the qualia of color : Against Physicalism (the idea that only physical/material things exist)
In Favor of Dualism or Non-Physicalist Views
Principle of univariance
An infinite set of different wavelength x intensity combinations can elicit exactly the same response as from a single type of photoreceptor. Therefore, one type of photoreceptor cannot make color discriminations based on wavelength.
Why do we have more than 1 cone cell type ?
The infinity of brightness and wavelength of light combinations makes it impossible to perceive color with a single type of cone cell
Each photoreceptor (cone cell) in the retina responds to light by generating a signal proportional to …
the amount of light it absorbs
A single photoreceptor cannot distinguish whether a strong response is due to:
- A bright but less preferred wavelength (e.g., a weakly absorbed color at high intensity).
- A dim but highly preferred wavelength (e.g., a strongly absorbed color at low intensity)
for every wavelength, there is a particular combination of activity across the three type of cones that remains constant across different _______
Intensities
True or false : Most “color-blind”/color-anommalous individuals can still make discriminations based on wavelength.
True
Deuteranope
- absence of M-cones.
- Everything looks yellowish
Protanope
- Due to absence of L-cones.
- Red and green defecit will make everything look yellow
Tritanope
- bsence of S-cones
- Blue/yellow discrimination issue
Cone monochromatipe
Has only one cone type; truly color-blind
Trichromacy
Theory that the color of any light is defined in our visual system by the relationships of three numbers, the outputs of three receptor types now known to be the three cones.
By mixing __ colors , we can reproduce any color
3 (red, green and blue)
Metamers
Different mixtures of wavelengths that look identical; more generally, any pair of stimuli that are perceived as identical in spite of physical differences
- When mixing two “pure” wavelengths (say green and violet), the combination of M and L- cone activity is identical to…
the combination resulting from a “pure” wavelength in the cyan frequency.
Additive Color Mixing
- process of creating colors by combining different wavelengths of light.
- primary colors are red, green, and blue (RGB). When all three are combined at full intensity, they produce white light.
- basis for color displays like TV screens and computer monitors.
Subtractive Color Mixing
- process of creating colors by removing (absorbing) certain wavelengths of light. T
- primary colors are cyan, magenta, and yellow (CMY). When combined, they absorb more light and produce darker colors, with all three mixing to form black.
E.g. Cyan paint : absorbs red, orange, yellow. It will reflect green and blue.
-used in printing, painting, and pigments.
Nonspectral hues
Hues that can arise only from mixtures of wavelengths activity across S, M and L-cones
i.e. there is no « purple » in the spectrum of visible light
Legal and illegal colors (Ewald Hering’s Opponent Colors Theory)
Legal colors:
* Bluish-green (cyan)
* Reddish-yellow (orange)
* Bluish-red (purple)
Illegal colors:
* Reddish-green
* Bluish-yellow
Opponent-process theory
Colors are processed in opposing pairs:
* Red vs. Green
* Blue vs. Yellow
Hue cancellation experiments
Participants adjust the amount of an “opponent” color (e.g., adding green to cancel out red) until no trace of the original hue remains. This helps map the sensitivity of the visual system to different color opponencies (red-green, blue-yellow)
Cones in general are very sensitive to the ______ of the light, for a wide range of wavelengths.
Intensity (why absolute level of activity of a particular cone type is relatively uninformative)
Opponent color theory in the cones
[L – M] or [M – L] compute red vs. green.
[L + M]= yellow]] – S or S – [L + M] compute blue vs. yellow.
_______ encodes general brightness
[L + M + S]
1 type of … cells will process blue-yellow opponency; another the red-green opponency
Center surround retinal ganglion
ex. the blue-yellow cell will respond more to blue in its center and yellow in its surround
Cones and their corresponding color
L and M stand for yellow
S for blue
M for green
L for red
Our visual system wants to be able to perceive color regardless of the _______ source.
Illuminating
Visual system is guessing what the illuminant is and is ________ it to guess the colour of the surface
Subtracting
Color constancy
Our brain discounts the illuminant by estimating the light source and adjusting our perception to
maintain stable colors across different lighting conditions.
Dress illusion
Perceiving blue and black : because you assume lot of yellow in illuminant
Perceiving white and gold : because you assume lot of blue in illuminant
