Sensation And Perception Ch. 5 Study Questions

Front 1

What is the problem of univariance?

Back 1

The problem 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 color discriminations based on wavelength.

Front 2

Describe the three types of cones in the human visual system and explain the differences between them.

Back 2

The three types of cones in the human visual system are: 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, the M-cones are preferentially sensitive to middle wavelengths, and the L-cones are preferentially sensitive to long wavelengths.

Front 3

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

Back 3

The trichromatic theory of color vision tells us that the color of any light is defined in our visual system by the relationships between a set of three numbers, the outputs of three receptor types now known to be the three cones.

Front 4

Why do metamers produce the same perceived color?

Back 4

Metamers are different mixtures of wavelengths that look identical. Even though the wavelengths themselves are different, the resulting mixture produces the same response from the cones in our visual system, which in turn causes the colors to appear identical

Front 5

What is an additive color mixture?

Back 5

An additive color mixture is 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.

Front 6

What is a subtractive color mixture?

Back 6

A subtractive color mixture is 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.

Front 7

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

Back 7

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 wavelength and a medium wavelength, and "blue" is equivalent to a short wavelength, the two lights will produce a mixture of short, medium, and long wavelengths. The resulting mixture will thus look white.

Front 8

Describe the idea of color space.

Back 8

Color space is the three-dimensional space, established because color perception is based on the outputs of three cone types, that describes the set of all colors.

Front 9

What does a color with zero saturation look like?

Back 9

A color with zero saturation looks white.

Front 10

What is the Young-Helmholtz theory?

Back 10

The Young-Helmholtz theory is the trichromatic theory of color vision, which was developed in the nineteenth century by Young and Helmholtz. It poses that any light is defined in our visual system by the relationships between a set of three numbers, the outputs of three receptor types (cones).

Front 11

Explain how the LGN is important in color perception.

Back 11

The LGN is a structure in the thalamus of the brain that receives input from the retinal ganglion cells and has input and output connections to the visual cortex. Some of its cells are maximally stimulated by spots of light, which are critical to color perception.

Front 12

What is a color-opponent cell?

Back 12

A color-opponent cell is a neuron whose output is based on a difference between sets of cones.

Front 13

What are the opponent color sets in the opponent color theory?

Back 13

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

Front 14

What is a unique hue? Provide an example.

Back 14

A unique hue is a color that can be described with only a single color term. Red is an example of a unique hue, as opposed to orange, which can be described as a compound (reddish yellow).

Front 15

What is a negative afterimage?

Back 15

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; yellow produces blue.

Front 16

Describe the method of "hue cancellation."

Back 16

The method of hue cancellation is used to demonstrate the opponent color theory. In this method, the experimenter might start with a light that appears to be a yellowish green. (S)he then cancels the yellowness by adding its opponent color, blue. The experimenter then measures the amount of blue light needed to just remove all traces of the yellow.

Front 17

What happens if the red-green and blue-yellow mechanisms are at their neutral points?

Back 17

If these two sets of opponents are at their neutral points, the stimulus will appear achromatic.

Front 18

What is achromatopsia?

Back 18

Achromatopsia is an inability to perceive colors that is due to damage to the central nervous system.

Front 19

In what way are color-anomalous individuals and cone monochromats color-blind?

Back 19

Color-anomalous individuals are individuals that can make discriminations based on wavelength, but these discriminations are different from the normal. Cone monochromats are individuals with only one cone type, and therefore they cannot discriminate different colors, leading them to be truly color-blind.

Front 20

What is cultural relativism?

Back 20

Cultural relativism is the idea that basic perceptual experiences such as color perception may be determined in part by the cultural environment.

Front 21

Describe the idea of color constancy.

Back 21

Color constancy is the tendency of a surface to appear the same color under a fairly wide range of illuminants.