Chapter 5 Questions Flashcards
What is the problem of univariance?
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 accurate color discriminations based on wavelength.
Describe the three types of cones in the human visual system and explain the differences between them.
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.
What does the trichromatic theory of color vision tell us about color perception?
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.
Why do metamers produce the same perceived color?
Metamers are different mixtures of wavelengths that nonetheless look identical. Even though the wavelength mixtures are different, they produce the same response from the cones in our visual system, which in turn causes the colors to appear identical.
What is an additive color mixture?
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.
What is a subtractive color mixture?
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 remainder contributes to the perception of color.
What happens if you shine “blue” and “yellow” lights on the same patch of paper?
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.
Describe the idea of color space.
Color space is a three-dimensional representation of all possible colors. The color space has three dimensions because color perception is based on the outputs of three cone types.
What does a color with zero saturation look like?
A color with zero saturation looks white.
Explain how the LGN is important in color perception.
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, which are critical to color perception.
What is a color-opponent cell?
A color-opponent cell is a neuron whose output is based on a difference between sets of cones.
What are the opponent color sets in the opponent color theory?
The opponent color sets in the opponent color theory are red versus green, blue versus yellow, and black versus white.
What is a unique hue? Provide an example.
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).
What is a negative afterimage?
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 color-opponent cells.
Describe the method of “hue cancellation.”
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. The experimenter 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.
