week 7 - perception of color

Question 1

selective reflection

Answer 1

objects that preferentially reflect some wavelengths

Question 2

selective transmission

Answer 2

transparent objects (like liquid) selectively allow wavelengths to pass through)

Question 3

Trichromatic theory of color (Young and Helmholtz)

Answer 3

3 different receptor mechanisms are responsible for vision

Question 4

What is the behavioral evidence for the trichromatic theory of color?

Answer 4

color-matching experiments

Question 5

What were the color matching experiments?

Answer 5

Observers adjusted amounts of three wavelengths in a comparison field to match a test field of one wavelength

Question 6

What were the results of the color-matching experiments?

Answer 6

• 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

Question 7

What is the physiological evidence for the trichromatic theory of color?

Answer 7

• 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

Question 8

What is color perception based on?

Answer 8

• response of 3 different cones
• responses vary on the available wavelengths

Question 9

High short wavelength activity

Answer 9

blue

Question 10

High medium wavelength activity

Answer 10

green

Question 11

high long wavelength activity

Answer 11

red

Question 12

high medium and long wavelength activity

Answer 12

yellow

Question 13

high activity in all wavelengths

Answer 13

white

Question 14

Are 3 receptors really necessary for color vision?

Answer 14

• one receptor type results in tru color blindness
• two receptor types may solve the problem but three receptors allows for perception of more colors

Question 15

3 different types of color defiencies

Answer 15

• monochromat
• dichromat
• anomalous trichromat

Question 16

monochromat

Answer 16

person who needs only one wavelength to match color

Question 17

dichromat

Answer 17

person who needs only two wavelengths to match color

Question 18

anomalous trichromat

Answer 18

needs 3 wavelengths in different proportions than normal trichromate

Question 19

opponent process theory of color (Hering)

Answer 19

• 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

Question 20

What is the behavioral evidence for the opponent-process theory color of vision?

Answer 20

• 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

Question 21

What is the physiological evidence for the opponent-process theory of color?

Answer 21

Researchers performing single-cell recordings found opponent neurons

Question 22

opponent neurons

Answer 22

• Respond in an excitatory manner to one end of the spectrum and an inhibitory manner to the other
• located in retina and LGN

Question 23

What are the differences in the trichromatic and opponent-process theories?

Answer 23

• 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

Question 24

What are the two types of opponent neurons in the cortex?

Answer 24

• single-opponent neurons
• double-opponent neurons