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14 Cards in this Set

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Objective

Distinguish between rods and cones.
Rods are types of visual receptors (120 million) that are mostly found in the periphery of the human retina.
Most sensitive to low levels of light Provide poor acuity

Cones are receptors (6 million) that are more prevalent in the central retina (fovea)
Sensitive to bright light
Provide excellent acuity
Essential for color vision
Objective

Distinguish the three major theories of color vision.
1. Young-Helmholtz Theory
2. Opponent-Process Theory
3. Retinex Theory
Objective

Explain how color blindness occurs.
For genetic reasons, some people lack one or two types of cones. Some have all three kinds, but one kind has abnormal properties.

In the most common form of color vision deficiency, people have distinguishing red from green because their long and medium wavelengt cones have the same photopigment instead of different ones.

The gene causing this deficiency is on the X chromosome.
rods
Receptors that are abundant in the periphery of the human retina

Respond to faint light
Not useful in bright daylight because bright light bleaches them
cones
Receptors that are most abundant in and around the fovea

Less active in dim light
More useful in bright light
Essential for color vision
photopigment
Chemicals that release energy when struck by light
Trichromatic (Young-Helmholtz) Theory
Theory that states that we perceive color through the relative rates of response by three kinds of cones, each kind normally sensitive to a different set of wavelengths
psychophysical observations
Reports by observers concerning their perceptions of various stimuli
visual field
Part of the world that you see
negative color afterimage
A replacement of the red you have been starting at with green, green with red, yellow and blue with each other, and black and white with each other
Opponent-Process Theory
We perceive color in terms of paired opposites

Red vs. Green
Yellow vs. Blue
White vs. Black
color constancy
Ability to recognize the color of an object despite changes in lighting
retinex theory
The cortex compares information from various parts of the retina to determine the brightness and color for each area

Example: If the cortex notes a constant amount of green throughout a scene, it subtracts some green from each object to determine its true color
color vision deficiency
An impairment in perceiving color differences compared to other people