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motionless flies. But let one zoom by and the frog’s “bug detector” cells snap awake. (As
Kermit the Frog said, “Time’s fun when you’re having flies.”)
• Male silkworm moths’ odor receptors can detect one-billionth of an ounce of chemical
sex attractant per second, released by a female one mile away (Sagan, 1977). That is why
there continue to be silkworms.
CULTURAL In Module 1.6, we’ll look at what psychologists have learned about how we sense our
AWARENESS world; in Module 2.1, we’ll explore how we perceive our world. Let’s begin by considering
Pay close attention to the difference some basic principles of both sensation and perception.
between sensation and perception.
Many people mistakenly believe that
the brain perceives situations in an Basic Concepts of Sensation and Perception
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
objective, calculating way. In fact,
the brain implements a number of How do we create meaning from the blizzard of sensory stimuli that bombards our body
biases and filters that influence our 24 hours a day? In its silent, cushioned, inner world, our brain floats in utter darkness. By
experience in the world, and those itself, it sees nothing. It hears nothing. It feels nothing. So, how does the world out there get
applied are often influenced by our
culture. in? To phrase the question scientifically: How do we construct our representations of the
external world? How do a campfire’s flicker, crackle, heat, and smoky scent activate neural
connections? And how, from this living neurochemistry, do we create our conscious experi-
ence of the fire’s motion and temperature, its aroma and beauty?

sensation the process by
which our sensory receptors Processing Sensations and Perceptions
and nervous system receive and Indiana Adams’ curious mix of perfect vision and face blindness illustrates the distinction
represent stimulus energies from between sensation and perception. When she looks at a friend, her sensation is normal: Her
our environment.
sensory receptors detect the same information any sighted person’s would, and her nervous
sensory receptors sensory
nerve endings that respond to system transmits that information to her brain. Her perception — the processes by which her
brain organizes and interprets sensory input — is almost normal (see Module 2.1). Thus, she may
stimuli. Copyright © Bedford, Freeman & Worth Publishers.
perception the process by recognize people from their hair,
which our brain organizes and gait, voice, or particular physique,
interprets sensory information, just not from their face. Her expe-
enabling us to recognize objects rience is much like the struggle
and events as meaningful.
any human would have trying to
bottom-up processing recognize a specific penguin.
information processing that Under normal circumstan-
begins with the sensory
receptors and works up to the ces, sensation and perception
brain’s integration of sensory blend into one continuous
information. process. In this module and
top-down processing Module 2.1, we slow down that
information processing process to study its parts; in
guided by higher-level mental real life, your sensory and per-
processes, as when we construct ceptual processes work toge-
perceptions drawing on our
experience and expectations. ther to help you decipher the
world around you. As your
brain absorbs the information
in Figure 1.6-1, bottom-up
processing enables your sen-
sory systems to detect the lines,
Figure 1.6-1
What’s going on here? angles, and colors that form the
images. Using top-down pro-
Our sensory and perceptual
processes work together to help cessing, you interpret what your
us sort out complex images, senses detect. We miss our
including the hidden donkey rider own typos because we know
in Sandro Del-Prete’s drawing, © Sandro Del-Prete what we intended, which (top-
Homage to Leonardo de Vinci. down) controls what we read.

116 Unit 1 Biological Bases of Behavior

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