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Module 1.6b Sensation: Vision

LEARNING TARGETS
1.6-4 Explain the characteristics of the energy that we see as visible light, and
describe the structures in the eye that help focus that energy.
®
AP Exam Tip 1.6-5 Describe how the rods and cones process information, and explain the path
information travels from the eye to the brain.
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
There’s a lot of vocabulary here. 1.6-6
Make sure you understand the Explain how we perceive color in the world around us.
name and the function of each 1.6-7 Describe the location and explain the function of feature detectors.
part of the eye. To learn how all
we perceive as brightness or Copyright © Bedford, Freeman & Worth Publishers.
the parts fit together, it may help to 1.6-8 Explain how the brain uses parallel processing to construct visual
make rough sketches (you don’t perceptions.
need to be an artist to try this!) and
then compare your sketches with
Figures 1.6-7 and 1.6-9 . You’ll be
better off making several quick,
rough sketches than one time-
consuming, nicely drawn one. Light Energy and Eye Structures

1.6-4 What are the characteristics of the energy that we see as visible light?
1.6-4 What ar e the characteristics of the energy that we see as visible light?
What structures in the eye help focus that energy?
What structures in the eye help focus that energy?
wavelength the distance from
the peak of one light wave Our eyes receive light energy and transduce (transform) it into neural messages. Our
or sound wave to the peak brain — in one of life’s greatest wonders — then creates what we consciously see. How does
of the next. Electromagnetic
wavelengths vary from the short such a taken-for-granted yet extraordinary thing happen?
gamma waves to the long pulses
of radio transmission. The Stimulus Input: Light Energy
hue the dimension of color that When you look at a bright red tulip, the stimuli striking your eyes are not particles of the

is determined by the wavelength color red but rather pulses of electromagnetic energy that your visual system perceives as
of light; what we know as the
color names blue, green, and so red. What we see as visible light is but a thin slice of the wide spectrum of electromagnetic
forth. energy, ranging from imperceptibly short gamma waves to the long waves of radio trans-

intensity the amount of mission ( Figure 1.6-6 ). Other portions are visible to other animals. Bees, for instance, cannot
energy in a light wave or sound see what we perceive as red but can see ultraviolet light.
wave, which influences what Light travels in waves, and the shape of those waves influences what we see. Light’s

wavelength is the distance from one wave peak to the next ( Figure 1.6-7 ). Wavelength

loudness. Intensity is determined determines hue the color we experience, such as a tulip’s red petals or green leaves. A light

,
by the wave’s amplitude (height).

wave’s amplitude, or height, determines its intensity the amount of energy the wave con-
,
cornea the eye’s clear, tains. Intensity influences brightness ( Figure 1.6-7b ).
protective outer layer, covering
the pupil and iris. To understand how we transform physical energy into color and meaning, we need to
know more about vision’s window — the eye.
pupil the adjustable opening
in the center of the eye through
which light enters. The Eye

iris a ring of muscle tissue that Light enters the eye through the cornea which bends light to help provide focus. The light

,
forms the colored portion of then passes through the pupil a small adjustable opening. Surrounding the pupil and
,

the eye around the pupil and
,

controls the size of the pupil controlling its size is the iris a colored muscle that dilates or constricts in response to light
opening. intensity. Each iris is so distinctive that iris-scanning technology can often confirm your
identity.
124 Unit 1 Biological Bases of Behavior
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