Chapter 5

Question 1

Describe the trichromatic theory.

Answer 1

Color information is encoded by a limited number of cones (3), and the activities of these cones encode color

Question 2

Describe the condition of monochromacy (possessing only one photopigment). Can people with this condition make wavelength discriminations?

Answer 2

No color discrimination
Certain wavelengths of light have a greater probability of being absorbed compared to others
This causes certain wavelengths to appear brighter, changing the color perception as well however with changing quanta, wavelength can appear to be made brighter causing the sam effect on the visual system (no wavelength discriminations)

Question 3

Describe the principal of univariance.

Answer 3

When a photopigment absorbs a wavelength of light, it does not encode the wavelength of that quantum
All info about the wavelength is lost

Question 4

Are monochromats colorblind?

Answer 4

Yes, they cannot distinguish objects based on wavelength alone

Question 5

If we show an individual with rod monochromacy three patches of light (505, 507, and 620nm) would they be able to distinguish and assign color?

Answer 5

Yes as differing amount of quantum are absorbed at each wavelength (more for 507 compared to 620nm)
Rhodopsin peak absorption is 507nm
505nm will be brightest, 620nm is dim

Question 6

How does a person with monochromacy distinguish color?

Answer 6

Deciphering brightness (red is dimmer then green)
Taking clues from familiar shapes (ex: red apple vs yellow banana)
They do not have the ability to distinguish stimuli from wavelength alone

Question 7

How can we test if a person can make wavelength based discriminations based on only wavelength?

Answer 7

Suppose the individual is shown two patches of light, one consisting of λa and the other of λ b, and asked to adjust the intensity of λb so that the two patches appear identical. If capable of matching these two wavelengths, the individual does not have the ability to make wavelength- based discriminations. If, however, the person is unable to match these two patches of light, he or she possesses the ability to make discriminations based purely on wavelength.

Question 8

Can a person with dichromacy and trichromacy adjust intensities so each path has same effect on visual system?

Answer 8

Yes

Question 9

Define metamers.

Answer 9

2 stimuli that appear identical, but are physically different (dichromacy)

Question 10

Can a dichromat (person with 2 photopigments) have color discrimination?

Answer 10

Yes if the absorptions spectra of the photopigments overlap

A combo of two wavelengths can be adjusted to make the patches appear equal

Question 11

What is the most common amount of photopigments in humans? How many wavelengths do they need in order to make discriminations?

Answer 11

3 photopigments
Trichromacy
S, M, L
Superior

4 wavelengths on 2 patches can be adjusted to look identical

Question 12

What portion of the cone determine absorption characteristics?

Answer 12

Opsin

Question 13

What chromosome are M and L cones on?

Answer 13

X (sex linked)

Question 14

What chromosome if S pigment on? What chromosome is rhodopsin on?

Answer 14

Chromosome 7

Chromosome 3

Question 15

Do human photopigments share a common ancestor?

Answer 15

Yes

(M and L are very similar)

Question 16

How do we describe color?

Answer 16

Hue
Saturation
Brightness

Question 17

Define hue. What is the physical stimulus for it?

Answer 17

Layperson’s term for color
Wavelength (intensity)

Question 18

Define saturation. What is the physical stimulus for it?

Answer 18

Fullness or purity of color

Both wavelength and colorimetric purity (excitation purity)

Question 19

Define brightness. What is the physical stimulus for it?

Answer 19

Brightness
Radiance

Question 20

What is hue dependent on?

Answer 20

Wavelength and stimulus brightness

Question 21

Describe invariant wavelengths.

Answer 21

As intensity of monochromatic stimulus changes the hue changes except for 3 wavelength (invariant)

478 nm (unique blue)
503 nm (unique green)
578 nm (unique yellow)

Question 22

What is the effect of increased intensity on hue?

Answer 22

For stimuli shorter than unique green (503 nm), as intensity increases, the stimulus appears more blueish

For stimuli longer than unique green, as intensity increases, the stimulus appears more yellowish

Question 23

Is saturation wavelength dependent?

Answer 23

Yes

570nm stimulus is less saturated then a monochromatic stimulus of any other wavelength

As wavelength increases saturation decreases, stope at 570nm as the minimum then increases as wavelength increases

Question 24

Where are the region of best wavelength discrimination?

Answer 24

490nm and 590nm

Worse at shorter and longer wavelengths

Question 25

What is wavelength discrimination?

Answer 25

The difference in wavelength that is needed so that the left and right side of the field no longer match

Question 26

What is color constancy?

Answer 26

Color remain relatively constant under varying lighting conditions

Colors are perceived relative to adjacent and surrounding objects

Question 27

Describe the encoding of color information.

Answer 27

Color is processed by bipolar hue channels

Red-green can signal only red or green not both simultaneously (same for blue-yellow)

Brightness encoded by separate white black channel

Question 28

Describe color opponent neuron.

Answer 28

Short wavelength stimuli cause inhibition (action potentials), long cause excitation

Median at 570nm

Question 29

Describe non color opponent neuron.

Answer 29

All wavelengths result in increase of action potential
Monochromatic has no color coding abilities
Peak at 555nm (combo of M and L)

Question 30

Where does color opposition first take place in the visual system?

Answer 30

Bipolar cells

Question 31

What 3 pathways transmit information leaving the retina to the LGN?

Answer 31

Magno (achromatic luminance)
Parvo (red-green)
Konio (blue-yellow)

Question 32

How can we specify colors using primaries?

Answer 32

We can specify colors by providing the amounts of 3 primaries that will produce the color

Wavelength to be matched (v) on one side, primaries on the other side (red, blue green) the amount of these primaries are adjusted until a perfect match is found

Red is required negative for 450-525nm
Blue shortest
Red longest
Green middle

Question 33

What is the CIE chromaticity diagram?

Answer 33

Shows the amount of imaginary primaries required to match any real color
Primaries are Imaginary to avoid use of negative quantities

Question 34

How are complementary wavelengths connected on CIE?

Answer 34

W line straight across