UFO sightings seem to be on the increase
just about everywhere. In February, a boy on a
passenger jet bound for Massachusetts was film-
ing another jet flying some distance away when
his camera recorded an unidentified object whiz-
zing by his window. In January, someone posted
a video of at least eight objects flying across
the sky in Mexico. Sightings have increased off
the coast of Cape Town, South Africa, and there
have even been reports that a UFO was spotted
moving across the sky near the InternationalSpace Station, which orbits about 250 miles
above the Earth.
One of the earliest UFO accounts occurred
in the late 1940s, when a rancher noticed
some strange objects strewn about his property
near Roswell, New Mexico. When the Air Force
quickly blocked off and cleared the site, sto-
ries circulated that a spacecraft had crashed
and that alien corpses had been recovered.
Thousands of believers in UFOs still flock to the
International UFO Museum in Roswell.W
hy do some people insist that they have
seen UFOs despite the skepticism of
others, who scoff and dismiss these objects
as planes and planets in the night sky? The
answer is that our sensations often deceive
us, and not just when we are looking up at
mysterious objects in the sky. “I saw it with
my own eyes!” people exclaim, as they tell of
seeing an image of Jesus on a garage door,
Osama bin Laden’s face in smoke billowing
from the doomed World Trade Center, the
Virgin of Guadalupe in a tortilla, or Mother
Teresa’s face in a cinnamon bun. These illu-
sions seem perfectly real to the people who
see them. Why do such reports turn up all
over the world, often with specific details?
In this chapter, we will answer these
questions by exploring how our senses take
in information from the environment and
how our brains use this information to con-
struct a model of the world. We will focus
on two closely connected sets of processes
that enable us to know what is happening
both inside our bodies and in the world
beyond our own skins. The first, sensation,
is the detection of physical energy emitted
or reflected by physical objects. The cells
that do the detecting are located in the
sense organs—the eyes, ears, tongue, nose,
skin, and internal body tissues. Sensory
processes produce an immediate awareness
of sound, color, form, and other building
blocks of consciousness. Without sensation,
we would lose touch—literally—with reality.
But to make sense of the world imping-
ing on our senses, we also need perception, a
set of mental operations that organizes sen-
sory impulses into meaningful patterns. Our
sense of vision produces a two- dimensional
image on the back of the eye, but we per-
ceive the world in three dimensions. Our
sense of hearing brings us the sound of a
C, an E, and a G played simultaneously on
the piano, but we perceive a C-major chord.
Sometimes, a single sensory image produces
two alternating perceptions, and the result is
an image that keeps changing, as illustrated
by the two examples on the next page.
Sensation and perception are the foun-
dation for learning, thinking, and acting.
Findings about these processes are often
put to practical use, as in the design of
industrial robots and in the training of as-
tronauts, who must make crucial decisions
based on what they sense and perceive.
An understanding of sensation and percep-
tion can also help us think more critically
about our own experiences and encourages
in us a certain humility: Usually we are
sure that what we sense and perceive must
be true, yet sometimes we are just plain
wrong. As you read this chapter, you will
sensation The detection
of physical energy emit-
ted or reflected by physi-
cal objects; it occurs
when energy in the exter-
nal environment or the
body stimulates receptors
in the sense organs.perception The pro-
cess by which the brain
organizes and interprets
sensory information.