Perception Of Color

Question 1

Cone sensitive to middle wavelengths; known as “green cone”

Answer 1

M-cone (middle)

Question 2

A cone that is preferentially sensitive to long wavelengths; known as “red cone”

Answer 2

L-cone (long)

Question 3

A cone that is preferentially sensitive to short wavelengths; colloquially (but not accurately known as a “blue cone”

Answer 3

S-cone (short)

Question 4

A mixture of lights. If light A and light B are both reflected from a surface to the eye, in the perception of color the effects of those two lights add together.

Answer 4

additive color mixture

Question 5

A mixture of pigments. If pigments A and B mix, some of the light shining on the surface will be subtracted by A, and some by B. Only the remainder contributes to the perception of color.

Answer 5

subtractive color mixture

Question 6

A structure in the thalamus, part of the midbrain, that receives input from the retinal ganglion cells and has input and output connections to the visual cortex.

Answer 6

lateral geniculate nucleus (LGN)

Question 7

A cell type—found in the retina, lateral geniculate nucleus, and visual cortex—that, in effect, subtracts one type of cone input from another.

Answer 7

cone-opponent cell

Question 8

A photopigment, found in a class of photoreceptive retinal ganglion cells, that is sensitive to ambient light.

Answer 8

melanopsin

Question 9

The theory that perception of color is based on the output of three mechanisms, each of them resulting from an opponency between two colors: red-green, blue-yellow, and black-white.

Answer 9

opponent color theory

Question 10

A cell type, found in the visual cortex, in which one region is excited by one cone type, combination of cones, or color and inhibited by the opponent cones or color (e.g., R+/G–).

Answer 10

double-opponent cell

Question 11

Another way to refer to cone-opponent cells, in order to differentiate them from double-opponent cells.

Answer 11

single-opponent cell

Question 12

An individual with only one cone type. These individuals are truly color-blind.

Answer 12

cone monochromat

Question 13

An individual with no cones of any type. In addition to being truly color-blind, these individuals are badly visually impaired in bright light.

Answer 13

rod monochromat

Question 14

A failure to recognize objects in spite of the ability to see them. Typically due to brain damage.

Answer 14

agnosia

Question 15

An inability to name objects in spite of the ability to see and recognize them (as shown by usage).

Answer 15

Anomia is typically due to brain damage

Question 16

A color perception effect in which the color of one region induces the opponent color in a neighboring region.

Answer 16

color contrast

Question 17

An afterimage whose polarity is the opposite of the original stimulus

Answer 17

negative afterimage

Question 18

The three types of cones in the human visual system are

Answer 18

S-cones, M-cones, and L-cones. They are all collectively responsible for discriminating between different colors. The S-cones are preferentially sensitive to short wavelengths (e.g., “blue”), the M-cones are preferentially sensitive to middle wavelengths (e.g., “green”), and the L-cones are preferentially sensitive to long wavelengths (e.g., “red”).

Question 19

The three steps to color vision are

Answer 19

1) Detection during which wavelengths of light are first registered by the visual system; 2) Discrimination during which different wavelengths of light are distinguished from each other; and 3) Appearance during which viewing conditions are taken into account while producing the final percept of a scene.

Question 20

What is the principle of univariance

Answer 20

The principle of univariance is the fact that an infinite set of different wavelength–intensity combinations can elicit exactly the same response from a single type of photoreceptor. One photoreceptor type cannot make accurate color discriminations by itself.

Question 21

What does the trichromatic theory of color vision tell us about color perception?

Answer 21

The trichromatic theory of color vision tells us that the color of any light is defined in our visual system by the relationships between the outputs of the three cone types.

Question 22

What is an additive color mixture?

Answer 22

An additive color mixture is when two sources of illumination combine to make a new color, as when mixing lights. If light A and light B are both reflected from a surface to the eye, the colors of those two lights add together.

Question 23

What is a subtractive color mixture?

Answer 23

A subtractive color mixture is when one source of illumination is subtracted from another, as when two color filters are placed in front of a light source or when pigments are mixed. If pigments A and B mix, some of the light shining on the surface will be subtracted by A, and some by B. Only the remaining light that was not absorbed by either A or B contributes to the perception of color.

Question 24

What happens if you shine “blue” and “yellow” lights on the same patch of paper?

Answer 24

If you shine “blue” and “yellow” lights on the same patch of paper, the wavelengths will add, producing an additive color mixture. Since “yellow” is equivalent to a mix of long and medium wavelengths, and “blue” consists of short wavelengths, the two lights will produce a mixture of short, medium, and long wavelengths. The resulting mixture will therefore look “white.”

Question 25

why is LGN important in color perception.

Answer 25

The LGN is a structure in the thalamus of the brain that receives input from retinal ganglion cells and has input and output connections to the visual cortex. Some of its cells are maximally stimulated by spots of light in a center–surround architecture, which is critical to color perception. The LGN contains cone-opponent cells that essentially subtract one type of cone input from another in a center–surround manner.

Question 26

What are the opponent color sets in opponent color theory?

Answer 26

The opponent color sets in opponent color theory are red vs. green, blue vs. yellow, and black vs. white.

Question 27

What is a negative afterimage?

Answer 27

A negative afterimage is a type of afterimage whose polarity is the opposite of the original stimulus. For instance, light stimuli produce dark negative afterimages. Colors are complementary: red produces green afterimages and yellow produces blue afterimages. The negativity of the afterimages arises from the cone-opponent cells.

Question 28

What is a double-opponent cell?

Answer 28

A double-opponent cell is a neuron whose output is based on a difference between sets of cones and is more complicated than a cone-opponent cell. In double-opponent cells, the center region is excited by one cone type and inhibited by another (e.g., R+/G–) and the surround has the opposite arrangement (e.g., G+/R–).