UIUC - PSYC 230 - PSYC230 EXAM #2 STUDY GUIDE! - Study Guide

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Important Concepts to know for Exam #2! Chapter #5 1. Definition of the three steps to color perception (detection,
discrimination, appearance) Detection: wavelengths of light must be detected in the first place Discrimination: we must be able to tell the difference between one, or a
mixture of, wavelengths from each other Appearance: we want to assign perceived colors to lights and surfaces in the
world and have those perceived colors be stable over time, regardless of
different lighting conditions 2. Color detection: Photoreceptors involved: S-cones, M-cones, L-cones (detect short, medium,
and long wavelengths) Photopic: light intensities that are bright enough to stimulate the cone
receptors and bright enough to “saturate” the rod receptors (cones are
sensitive to photopic lighting conditions) Scotopic: light intensities that are bright enough to stimulate the rod
receptors but too dim to stimulate the cone receptors (rods are sensitive to
scotopic lighting conditions) 3. Color discrimination: The Problem of Univariance: an infinite set of different wavelength-intensity
combinations can elicit exactly the same response from a single type of
photoreceptor  Rods suffer from the problem of univariance, which makes them unable
to detect color because they don’t have specialized photoreceptors to
detect different wavelengths like cones do (S, M, L cones) Trichromatic Theory of Color (Trichromacy): the theory that the color of any
light is defined in our visual system by the relationships of 3 numbers, the
outputs of 3 receptor types (cones) Maxwell’s Color Matching Experiments: experiments done to match colors of
light. Young and Helmholtz (who created theory of trichromacy) worked on
their theory based on these results. Metamers: mixtures of different wavelengths that look identical OR any pair
of stimuli that are perceived as identical in spite of physical differences. Ex.)
total stimulation of M cone = total stimulation of L cone.

Important Concepts to know for Exam #2! Additive Color Mixing: 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 2 lights add together. Subtractive Color Mixing: a mixture of pigments. If pigment 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. Cone Opponent Cells: a neuron whose output is based on a difference
between sets of cones. Step 1: detection (S, M, L cones detect light) Step 2:
cone-opponent mechanisms discriminate wavelengths.  [L-M] computes green (L comes before M, G comes before R)  [M-L] computes red (opposite ^)  S-[M+L] computes blue (SML = small, like baby blue)  [M+L]-S computes yellow (no trick to remember this one sorry) 4. Color appearance: Color Space: a 3D space that describes all colors. There are several possible
color spaces. RGB Color Space: defined by the outputs of short, medium, and long
wavelength lights HSB Color Space: defined by hue, saturation, and brightness. Hue is the
chromatic (color) aspect of light, saturation is the chromatic strength of the
hue, and brightness is the distance from black in color space. Opponent Color Theory: the theory that perception of color is based on the
output of 2 mechanisms, each of them based on an opponency between 2
colors: red and green, blue and yellow, black and white. Hering’s Work: Hering noticed that some color combinations are legal while
others are illegal. For example, we can have reddish yellow (orange), bluish
red (purple), and bluish green. We cannot have reddish green or bluish
yellow. We can use the hue cancellation paradigm to determine the
wavelengths of unique hues. Hue Cancellation Paradigm: shown a color and have to adjust to make
another color. To get rid of a color, add it’s opposite on the opponent color
circle Unique Hue: any of the 4 colors that can be described with only a single color
term (red, etc.) Achromatopsia: an inability to perceive colors; caused by damage to the
central nervous system

Important Concepts to know for Exam #2! Afterimage: a visual image seen after a stimulus has been removed Negative Afterimage: an afterimage whose polarity is the opposite of the
original stimulus 5. Basic principles of color perception: Types of colorblind people: Deuteranope, Protanope, Tritanope, color
anomalous, cone Monochromat, rod Monochromat. Definitions for each
of these are in the class slides, I’m not sure if we need to have them
memorized but cone Monochromat is truly colorblind because there’s only
one type of cone present. Rod Monochromat is truly color blind with bad
visual impairment because these people have no cones of any type. Cultural Relativism: in sensation and perception, the idea that basic
perceptual experiences (color perception) may be determined in part by the
cultural environment Color Contrast: a color perception effect in which the color of one region
induces the opponent color in a neighboring region (examples of these in
pictures are found in the class slides) Color Assimilation: a color perception effect in which 2 colors bleed into each
other, each taking on some of the chromatic quality of the other Watercolor Illusion: brighter chromatic contour on the inside and darker
chromatic contour on the outside creates the illusion that the brighter color
spreads into the entire enclosed area Color Constancy: a tendency of a surface to appear the same color under a
fairly wide range of illuminants Color processing occurs in nature to aid animals in finding food easier,
helps bees to trade food for pollination, indicates the sex of the animal in
some species, or sexual signs. 6. Synesthesia Synesthesia: accidental association of 2 percepts, with one perception
eliciting a secondary perception (2 or more). Stimulation or sensory or
cognitive pathway leads to automatic, involuntary experiences in a second
sensory or cognitive pathway. 4% of the population. Examples: music &
color, taste & color. Most common type: grapheme  color synesthesia. Chapter #6 1. Definitions

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