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Module 1.6b

®
AP Science Practice Check Your Understanding

Examine the Concept Apply the Concept

Some nocturnal animals, such as toads, mice, rats, and If someone had asked you “Is grass green?” before you read

bats, have impressive night vision thanks to having many this section, how would you have responded? Explain why your
more ____________ (rods/cones) than ____________ (rods/ response might be different now.
cones) in their retinas. These creatures probably have very poor Consider your activities in the last day. Which of them relied

____________ (color/black-and-white) vision. on your rods? Which relied on your cones? Explain why these
Cats are able to open their ____________ activities would be different — or impossible — without these
much wider than we can, which allows cells’ different abilities.
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
more light into their eyes so they can Explain the rapid sequence of events that occurs when you

see better at night. see and recognize a friend.

Explain the difference between
the two key theories of color
Copyright © Bedford, Freeman & Worth Publishers.
vision. Are they contradictory or Kruglov_Orda/Shutterstock
complementary? Explain.

Answers to the Examine the Concept questions can be found in Appendix C at the end of the book.

Module 1.6b REVIEW

1.6-4 What are the characteristics of the energy Contemporary research has found three types of cones,
that we see as visible light? What structures in the each most sensitive to the wavelengths of one of the three
eye help focus that energy? primary colors of light (red, green, or blue).
• Hering’s opponent-process theory proposed three additional
• What we see as light is only a thin slice of the broad spec- sets of opposing retinal processes (red-green, blue-
trum of electromagnetic energy. The portion visible to hu- yellow, white-black). Research has confirmed that, en
mans extends from the shorter blue-violet wavelengths to route to the brain, neurons in the retina and the thalamus
the longer red wavelengths.
code the color-related information from the cones into
• After entering the eye through the cornea, passing through pairs of opponent colors.

the pupil and iris, and being focused by the lens, light energy These two theories, and the research supporting them,

particles (from a thin slice of the broad spectrum of electro- • show that color processing occurs in two stages.
magnetic energy) strike the eye’s inner surface, the retina.
• Wavelength determines hue, the color we perceive; ampli- 1.6-7 Where are feature detectors located, and

tude determines intensity, the brightness we perceive what do they do?
.

1.6-5 How do the rods and cones process • Feature detectors, specialized nerve cells in the visual cor-
information, and what is the path information travels tex, respond to specific features of the visual stimulus,
from the eye to the brain? such as shape, angle, or movement.

• Light entering the eye triggers chemical changes that • Feature detectors pass information on to other cortical areas,
convert light energy into neural impulses. where supercell clusters respond to more complex patterns.
• Photoreceptors called cones and rods at the back of the 1.6-8 How does the brain use parallel processing to

retina provide differing sensitivities — cones to detail and construct visual perceptions?
color, rods to faint light and peripheral motion.
• After processing by bipolar and ganglion cells, neural im- • Through parallel processing, the brain handles many aspects
pulses travel from the retina through the optic nerve to the of vision (color, movement, form, and depth) simultane-
thalamus, and on to the visual cortex. ously. Other neural teams integrate the results, comparing
them with stored information and enabling perceptions.
1.6-6 How do we perceive color in the world around us?

• The Young–Helmholtz trichromatic (three-color) theory pro-
posed that the retina contains three types of color receptors.
Sensation: Vision Module 1.6b 133

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