week 7 - perception of color Flashcards
selective reflection
objects that preferentially reflect some wavelengths
selective transmission
transparent objects (like liquid) selectively allow wavelengths to pass through)
Trichromatic theory of color (Young and Helmholtz)
3 different receptor mechanisms are responsible for vision
What is the behavioral evidence for the trichromatic theory of color?
color-matching experiments
What were the color matching experiments?
Observers adjusted amounts of three wavelengths in a comparison field to match a test field of one wavelength
What were the results of the color-matching experiments?
- Observers with normal color vision need at least three wavelengths to make matches
- Observers with color deficiencies can match colors by using only two wavelengths
What is the physiological evidence for the trichromatic theory of color?
- researchers measured absorption spectra of visual pigments in receptors and found that they responded to short, medium, and long wavelengths
- researchers found genetic differences for coding proteins for the three pigments
What is color perception based on?
- response of 3 different cones
- responses vary on the available wavelengths
High short wavelength activity
blue
High medium wavelength activity
green
high long wavelength activity
red
high medium and long wavelength activity
yellow
high activity in all wavelengths
white
Are 3 receptors really necessary for color vision?
- one receptor type results in tru color blindness
- two receptor types may solve the problem but three receptors allows for perception of more colors
3 different types of color defiencies
- monochromat
- dichromat
- anomalous trichromat
monochromat
person who needs only one wavelength to match color
dichromat
person who needs only two wavelengths to match color
anomalous trichromat
needs 3 wavelengths in different proportions than normal trichromate
opponent process theory of color (Hering)
- color vision is caused by opposing responses generated by blue and yellow, and by green and blue
- responses are believed to be the result of chemical reactions in the retina
What is the behavioral evidence for the opponent-process theory color of vision?
- color after images and simultaneous color contrast show the opposing pairings (ex. green and yellow American flag)
- types of color blindness are red/green and blue/yellow
What is the physiological evidence for the opponent-process theory of color?
Researchers performing single-cell recordings found opponent neurons
opponent neurons
- Respond in an excitatory manner to one end of the spectrum and an inhibitory manner to the other
- located in retina and LGN
What are the differences in the trichromatic and opponent-process theories?
- Trichromatic: explains the responses of the cones in the retina
- Opponent-process: explains neural response for cells connected to the cones further in the brain
What are the two types of opponent neurons in the cortex?
- single-opponent neurons
- double-opponent neurons