Invitation to Psychology

204 Chapter 6 Sensation and Perception

Just as there are size, shape, location, bright-

ness, and color constancies, so there are size,

shape, location, brightness, and color inconstan-

cies, resulting in illusions. The perceived color of

an object depends on the wavelengths reflected

by its immediate surroundings, a fact well known

to artists and interior designers. That is why you

never see a good, strong red unless other objects

in the surroundings reflect the blue and green part

of the spectrum. When two objects that are the

same color have different surroundings, you may

mistakenly perceive them as different.

Perhaps the ultimate perceptual illusion oc-

curred when Swedish researchers tricked people

into feeling that they were swapping bodies with

another person or even a mannequin (Petkova &

Ehrsson, 2008). The participants wore virtual-

reality goggles connected to a camera on the

other person’s (or mannequin’s) head. This al-

lowed them to see the world from the other body’s

point of view as an experimenter simultaneously

stroked both the participant’s body and the other

person’s (or mannequin’s) with a rod. Most people

soon had the weird sensation that the other body

was actually their own; they even cringed when

the other body was poked or threatened. The re-

searchers speculate that some day the body-swap-

ping illusion could be helpful in marital counsel-

ing, allowing each partner to literally see things

from the other’s point of view, or in therapy with

people who have distorted body images.

In everyday life, most illusions are harmless

and entertaining. Occasionally, however, an il-

lusion interferes with the performance of some

task or skill, or may even cause an accident. For

example, because large objects often appear to

move more slowly than small ones, drivers some-

times underestimate the speed of onrushing trains

at railroad crossings. They think they can beat the

train, with tragic results.

Watch the Video What’s In It For Me?:

Perceptual Magic in Art at MyPsychLab

Recite & Review

Recite: This instruction is no illusion: Recite everything you can remember about hue, brightness,

saturation, parts of the eye, rods and cones, the optic nerve, feature-detector cells, the trichromatic

and opponent process theories of color vision, Gestalt principles, binocular and monocular cues to

depth and distance, visual constancies, and visual illusions.

Review: That’s a lot of information to learn, so you’d do well to go back and read this section

again.

Now take this Quick Quiz:

1. From an evolutionary point of view, people are most likely to have specialized brain cells for
   recognizing (a) flowers, (b) bugs, (c) faces, (d) chocolate, (e) cars.


2. How can two Gestalt principles help explain why you can make out the Big Dipper on a starry
   night?


3. True or false: Binocular cues help us locate objects that are very far away.


4. Hold one hand about 12 inches from your face and the other one about 6 inches away.
   (a) Which hand will cast the smaller retinal image? (b) Why don’t you perceive that hand as
   smaller?
   Answers:

Study and Review at MyPsychLab

allows you to “fill closure of certain stars encourages you to see them as clustered together to form a pattern; Proximity2. c1.

The hand that is 12 inches away will cast a smaller retinal image. a. 4. false3. in the gaps” and see the contours of a “dipper.”

Your brain takes the differences in distance into account in estimating size; also, you know how large your hands are.b.

The result is size constancy.

You are about to learn...

•    the basics of how we hear.

•    why a note played on a flute sounds different

from the same note played on an oboe.

•    how we locate the source of a sound.

hearing

Like vision, the sense of hearing, or audition, pro-

vides a vital link with the world around us. Because

social relationships rely so heavily on hearing,

when people lose their hearing they sometimes

come to feel socially isolated. That is why many