Chapter 6.5

Question 1

black

Answer 1

experienced when there is an absence of light.

Question 2

white

Answer 2

produced by an intense mixture of a wide range of wavelengths in roughly equal proportions.

Question 3

gray

Answer 3

produced by the same mixture at lower intensities.

Question 4

color

Answer 4

depends on the wavelengths of light that it reflects into the eye.

Question 5

Component theory (trichromatic theory) of color vision

Answer 5

proposed by Young but refined by Helmholtz; there are three different kinds of color receptors (cones), each with a different spectral sensitivity, and the color of a particular stimulus is presumed to be encoded by the ratio of activity in the three kinds of receptors. Derived from the observation that any color of the visible spectrum can be matched by a mixing together of three different wavelengths of light in different proportions.

Question 6

Opponent-process theory of color vision

Answer 6

proposed by Hering; suggested that there are two different classes of cells in the visual system for encoding color and another class for encoding brightness. Each of the three classes of cells encoded two complementary color perceptions.

Question 7

one class of color coding cells (opponent-process theory)

Answer 7

signaled red by changing its activity in one direction (e.g. hyperpolarization) and signaled red’s complementary color, green, by changing its activity in the other direction (e.g. hyperpolarization).

Question 8

another class of color coding cells (opponent-process theory)

Answer 8

signals blue and its complement yellow in the same opponent fashion.

Question 9

Opponent-process theory based on:

Answer 9

(1) Complementary colors cannot exist together.
(2) The afterimage produced by staring at red is green and vice versa and the after image produced by staring at yellow is blue and vice versa.

Question 10

Complementary colors

Answer 10

pairs of colors that produce white or gray when combined in equal measure.

Question 11

Cones each have a different photopigment

Answer 11

with its own characteristic absorption spectrum. Some are more sensitive to short, medium, or long wavelengths.

Question 12

At all subsequent levels of the retina-geniculae-striate system

Answer 12

there are cells that respond in one direction (e.g. increased firing) to one color and in the opposite direction (e.g. decreased firing) to its complementary color.

Question 13

Trichromats

Answer 13

most primates; possessing three color vision photopigments.

Question 14

Dichromats

Answer 14

most other mammals; possessing two color vision photopigments. Lack the photopigment sensitive to long wavelengths and thus have difficulty seeing light at the red end of the visible spectrum.

Question 15

color constancy

Answer 15

refers to the fact that the perceived color of an object is not a simple function of the wavelengths reflected by it. Tendency for an object to stay the same color despite major changes in the wavelengths of light that it reflects.

Question 16

Land

Answer 16

blue objects stay blue, etc., regardless of the wavelengths they reflect. This color constancy occurs as long as the object is illuminated with light that contains some short, medium, and long wavelengths and as long as the object is viewed as part of a scene, not in isolation.

Question 17

Retinex theory of color vision

Answer 17

Land; the color of an object is determined by its reflectance – the proportion of light of different wavelengths that a surface reflects. The visual system calculates the reflectance of surfaces, and thus perceives their colors, by comparing the light reflected by adjacent surfaces in at least three different wavelength bands (short, medium, long).

Question 18

Dual-opponent color cells

Answer 18

in the monkey visual cortex respond with vigorous “on” firing when the center of their circular receptive field is illuminated with one wavelength and the surround (periphery) is simultaneously illuminated with another wavelength. Display vigorous “off” firing when the pattern of illumination is reversed. In essence, they respond to the contrast between wavelengths reflected by adjacent areas of their receptive field. Not evenly distributed throughout the primary visual cortex.

Question 19

Livingstone and Hubel

Answer 19

found that dual-opponent color cells are concentrated in the primary visual cortex in peglike columns that penetrate the layers of the money primary visual cortex, with the exception of the lower layer IV. Many neurons are particularly rich in the mitochondrial enzyme cytochrome oxidase.