Invitation to Psychology

206 Chapter 6 Sensation and Perception

basis of the frequency of the basilar membrane’s

vibration; again, different frequencies lead to dif-

ferent neural codes.

Could you have ever imagined that hearing

depends on this complex and odd arrangement of

bristles, fluids, and snail shells?

Constructing the auditory World

Lo 6.18

Just as we do not see a retinal image, so we do not

hear a chorus of brushlike tufts bending and sway-

ing in the dark recesses of the cochlea. Instead, we

use our perceptual powers to organize patterns of

sound and to construct a meaningful auditory world.

In your psychology class, your instructor

hopes you will perceive his or her voice as figure

and distant cheers from the athletic field as ground.

Whether these hopes are realized will depend, of

course, on where you choose to direct your atten-

tion. Other Gestalt principles also seem to apply

to hearing. The proximity of notes in a melody

tells you which notes go together to form phrases;

continuity helps you follow a melody on one violin

when another violin is playing a different melody;

similarity in timbre and pitch helps you pick out

the soprano voices in a chorus and hear them as

a unit; closure helps you understand a cell phone

jackhammers, and music players turned up to

full blast, such damage is increasingly common,

even among teenagers and young adults (Agrawal,

Platz, & Niparko, 2008). Scientists are looking for

ways to grow new, normally functioning hair cells,

but hair-cell damage is currently irreversible.

The hair cells of the cochlea are embedded

in the rubbery basilar membrane, which stretches

across the interior of the cochlea. When pressure

reaches the cochlea, it causes wavelike motions in

fluid within the cochlea’s interior. These waves

of fluid push on the basilar membrane, causing

it to move in a wavelike fashion, too. Just above

the hair cells is yet another membrane. As the

hair cells rise and fall, their tips brush against

it, and they bend. This causes the hair cells to

initiate a signal that is passed along to the audi-

tory nerve, which then carries the message to the

brain. The particular pattern of hair-cell move-

ment is affected by the manner in which the

basilar membrane moves. This pattern determines

which neurons fire and how rapidly they fire,

and the resulting code in turn helps determine

the sort of sound we hear. We discriminate high-

pitched sounds largely on the basis of where activ-

ity occurs along the basilar membrane; activity at

different sites leads to different neural codes. We

discriminate low-pitched sounds largely on the

Auditory

canal

Auditory

nerve leading

to brain

Cochlea

Cochlea

Semicircular

canals Auditory

nerve

Basilar

membrane

Hair

cells (cilia)

Fluid

Oval

window

(membrane)

Middle ear cavity

Auditory

canal

Eardrum

“Hammer”

bone

“Anvil” bone

“Stirrup”

bone

Outer Ear Middle Ear Inner Ear

Figure 6.8 Major Structures of the ear

Sound waves collected by the outer ear are channeled down the auditory canal, causing the eardrum to vibrate. These

vibrations are then passed along to the tiny bones of the middle ear. Movement of these bones intensifies the force of

the vibrations separating the middle and inner ear. The receptor cells for hearing (hair cells), located in the organ of Corti

(not shown) within the snail-shaped cochlea, initiate nerve impulses that travel along the auditory nerve to the brain.