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vision
a system that converts light into neural activity; light is the stimulus, electromagnetic energy; most is invisible to human eye; visible light is a very small part of the electromagnetic spectrum
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properties of color
hue, saturation, brightness
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hue
color we see: blue, yellow, green, purple, etc.
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saturation
dominance of hue, shades; how pure is the color; intensity or richness; decrease saturation looks more washed out
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brightness
how strong is the color; varies based on strength of light entering eye; low brightness (dark/black), light brightness (light/white)
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the human eye
cornea, aqueous humor, pupil, iris, lens
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cornea
bends the light wave, protects the eye, contact lenses rest on it
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aqueous humor
a watery substance in back of cornea; keeps rounded and glazy; nourishes the eye
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pupil
an adjustable opening; constricts and dilates
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iris
a translucent, doughnut-shaped muscle; controls size of pupil
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lens
focus the visual image on the retina; one concave, one convex
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myopia
nearsightedness; close objects are seen clearly; distance objects are blurry; image focuses in front of retina
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hyperopia
farsightedness; distance objects are seen clearly; close objects are blurry; image is focused behind retina
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ciliary muscles
changes the shape of the lens to bend light rays; ocular accommodation
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ocular accommodation
close objects get rounder; far objects get less round
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vitreous humor
jelly-like substance, most of eye; gives shape to eye
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retina
a multilayered light-sensitive tissue; transduction occurs here; retinal image is upside down, flipped right-side up by brain; retinal focus may be improved with eyeglasses or contact lenses
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photoreceptors
in retina, perform transduction; 2 types: rods and cones
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rods
highly sensitive to light; function best in dim light; primarily black-and-white; not sensitive to color; located in periphery
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cones
less sensitive to light; better in bright light; distinguishes colors; concentrated in fovea (center)
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bipolar neurons
pass signals from photoreceptors to ganglion cells
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ganglion cells
on surface of retina; generate action potentials; make up the optic nerve
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fovea
a small area in the center of the retina; densely packed cones, contains no rods
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blindspot
point at which optic nerve exits the eye; no receptor cells
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light adaptation
increasing ability to see in the light as time in the light increases
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dark adaptation
increasing ability to see in the dark as time in the dark increases; going into a movie theater
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Trichromatic Theory (of color vision)
Young-Helmholtz; cones are most sensitive to wavelengths corresponding to blue, green, and red
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Three types of cones
short-wavelength, medium-wavelength, and long-wavelength
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short-wavelength
most sensitive to blue
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medium-wavelength
most sensitive to green
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long-wavelength
most sensitive to reddish-yellow
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limitations of the Trichromatic Theory
cannot explain some aspects of color vision; after image: ex. red, white, blue flag after staring at dot
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Opponent-Process Theory (of color vision)
color-sensitive visual elements are grouped into pairs; pair members oppose (inhibit) each other; red/green, blue/yellow, black/white; explains color afterimages
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Dual-Process Theory
combines the two theories to account for color perception; trichromatic cones are most sensitive to blue, green, and red; opponent processes begin in ganglion cells and beyond
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colorblindness
inability to sense certain colors
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trichromats
people with normal color vision
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dichromat
people who are color-blind in one of the three systems
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monochromat
peple who are completely color-blind; sensitive only to the black-white system; extremely rare; more common in boys
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Chemical senses
smell and taste; no animal is without some form of chemical sense
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olfactory perception
our sense of smell; nose, mouth, and upper part of throat; detects airborne chemicals; does not connect through the thalamus; connects through the olfactory bulb in brain; receives messages regarding smell
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gustatory
taste perception; mouth; detects chemicals in solutions that contact receptors in the mouth; about 10,000 taste buds in a person's mouth; grouped in a structure called papillae; most on the tongue
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human taste system detects
only a few elementary sensations: sweet, sour, bitter, and salty
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flavor
produced by an interaction between taste and smell; what makes food taste good are actually odors detected by the olfactory system; joins smell, taste, sight, texture, temperature, hunger, and satiety
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touch
people can function without vision, hearing , or smell; trouble surviving without touch; energy detected by the sense of touch, physical pressure; skin has hairs all over it; transduction occurs in the receptors in or just below the skin
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encoding of touch information: the skin encodes the intensity of a stimulus by
firing rate of individual neurons and the number of neurons stimulated
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