Page 141 - 2024-bfw-MyersAP4e

Module 1.6c

Because sound travels fast
and human ears are not very far Air Figure 1.6-21
apart, the intensity difference and How we locate sounds
the time lag are extremely small. Sound waves strike one ear
A just noticeable difference in the sooner and more intensely than
the other. From this information,
direction of two sound sources our nimble brain can compute
corresponds to a time difference the sound’s location. As you
of just 0.000027 second! Luckily might expect, people who lose
all hearing in one ear often have
for us, our supersensitive audi- difficulty locating sounds.
tory system can detect such min-
ute differences and locate the
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
sound (Brown & Deffenbacher, Sound
1979; Middlebrooks & Green, shadow
1991).
Copyright © Bedford, Freeman & Worth Publishers.

®
AP Science Practice Check Your Understanding

Examine the Concept Apply the Concept
▶ ▶The amplitude of a sound wave determines our perception of ▶ ▶Imagine you are attending a symphonic concert. Explain the
____________ (loudness/pitch). theories of pitch perception that best help you enjoy the sounds
▶ ▶The longer the sound waves are, the ____________ (lower/higher) of (1) a high-pitched piccolo and (2) a low-pitched cello.
their frequency and the ____________ (higher/lower) their pitch.
Answers to the Examine the Concept questions can be found in Appendix C at the end of the book.

Module 1.6c REVIEW

1.6-9 What are the characteristics of air pressure tiny hair cells, triggering neural messages to be sent (via
waves that we hear as sound? the thalamus) to the auditory cortex in the brain.
• Sensorineural hearing loss (or nerve deafness) results from
• Sound waves are bands of compressed and expanded air. damage to the cochlea’s hair cells or the auditory nerve.
Our ears detect these brief changes in air pressure. Conduction hearing loss results from damage to the me-
• Sound waves vary in amplitude, which we perceive as chanical system that transmits sound waves to the cochlea.
differing loudness (with sound intensity measured in Cochlear implants can restore hearing for some people.
decibels), and in frequency (measured in hertz), which we
experience as differing pitch. 1.6-11 How do we detect loudness, discriminate
pitch, and locate sounds?
1.6-10 How does the ear transform sound energy
into neural messages? • Loudness is not related to the intensity of a hair cell’s re-
sponse, but rather to the number of activated hair cells.
• The middle ear is the chamber between the eardrum and • Place theory (place coding) explains how we hear high-
the cochlea. pitched sounds, and frequency theory (temporal coding),
• The inner ear consists of the cochlea, semicircular canals, extended by volley theory, explains how we hear low-
and vestibular sacs. pitched sounds. A combination of the two theories
• Sound waves traveling through the auditory canal cause explains how we hear pitches in the middle range.
tiny vibrations in the eardrum. The bones of the middle ear • Sound waves strike one ear sooner and more intensely
amplify these vibrations and relay them to the fluid-filled than the other. The brain analyzes the minute differences
cochlea. Rippling of the basilar membrane, caused by pres- in the sounds received by the two ears and computes the
sure changes in the cochlear fluid, causes movement of the sound’s source.

Sensation: Hearing Module 1.6c 141

03_myersAPpsychology4e_28116_ch01_002_163.indd 141 15/12/23 9:26 AM