Psychology2016

108 CHAPTER 3

would correspond to saturation or purity in light is called timbre in sound, a richness in

the tone of the sound. And just as people rarely see pure colors in the world around us,

they also seldom hear pure sounds. The everyday noises that surround people do not

allow them to hear many pure tones.

Just as a person’s vision is limited by the visible spectrum of light, a person is also

limited in the range of frequencies he or she can hear. Frequency is measured in cycles

(waves) per second, or hertz (Hz). Human limits are between 20 and 20,000 Hz, with the

most sensitivity from about 2,000 to 4,000 Hz, very important for conversational speech.

(In comparison, dogs can hear between 50 and 60,000 Hz, and dolphins can hear up to

200,000 Hz.) To hear the higher and lower frequencies of a piece of music on their iPod®

or iPhone®, for example, a person would need to increase the amplitude or volume—

which explains why some people like to “crank it up.”

THE STRUCTURE OF THE EAR: FOLLOW THE VIBES The ear is a series of structures,

each of which plays a part in the sense of hearing, as shown in Figure 3. 11.

hertz (Hz)
cycles or waves per second, a mea-
surement of freSuency.

Figure 3.11 The Structure of the Ear

Pinna

Ear canal

Hammer

Anvil

Auditory

nerve

Eardrum

Cochlea

Vestibular organ

(semicircular canals)

Stirrup

Outer earMiddle ear Inner ear

Oval

window

CC

*funneling: moving to a focal point.

THE OUTER EAR The pinna is the visible, external part of the ear that serves as a kind of

concentrator, funneling* the sound waves from the outside into the structure of the ear.

The pinna is also the entrance to the auditory canal (or ear canal), the short tunnel that

runs down to the tympanic membrane, or eardrum. When sound waves hit the eardrum,

they cause three tiny bones in the middle ear to vibrate.

THE MIDDLE EAR: HAMMER, ANVIL, AND STIRRUP The three tiny bones in the middle ear

are known as the hammer (malleus), anvil (incus), and stirrup (stapes), each name stem-

ming from the shape of the respective bone. Collectively they are referred to as the ossicles

and they are the smallest bones in the human body. The vibration of these three bones

amplifies the vibrations from the eardrum. The stirrup, the last bone in the chain, causes

a membrane covering the opening of the inner ear to vibrate.

THE INNER EAR This membrane is called the oval window, and its vibrations set off

another chain reaction within the inner ear. The inner ear is a snail-shaped structure

called the cochlea, which is filled with fluid. When the oval window vibrates, it causes

pinna
the visiDle Rart of the ear.

auditory canal
short tunnel that runs from the pinna
to the eardrum.

cochlea
snail-shaped structure of the inner ear
that is filled with fluid.