Chapter 5 (M. Wolfe) Flashcards
Three steps to color perception.
1) Detection, 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.
The three types of cones in the human visual system and explain the differences between them.
The three types of cones are: S-cones, M-cones, and L-cones. They are all collectively responsible for discriminating between different colors. The S-cones are sensitive to short wavelengths (e.g., “blue”), the M-cones are sensitive to middle wavelengths (e.g., “green”), and the L-cones are sensitive to long wavelengths (e.g., “red”).
What is the principle of univariance?
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.
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 the trichromatic theory of color vision?
The trichromatic theory of color vision, developed in the nineteenth century by both Young and Helmholtz, proposes that any light is defined in our visual system by the relationships between a set of three numbers, which we now know to be the outputs of the three cone types.
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 remaining light that was not absorbed by either A or B contributes to the perception of color.
Explain why 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 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.
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.
What are the opponent color sets in opponent color theory?
The opponent color sets in opponent color theory are red vs. green, blue vs. yellow, and black vs. white.
What is a unique hue?
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).
The method of “hue cancellation.”
It is used to demonstrate 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 remove all traces of yellow.
What is a negative afterimage?
It 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.
