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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
sooner and more intensely than
A just noticeable difference in the 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
sound (Brown & Deffenbacher, Sound
1979; Middlebrooks & Green, shadow
1991). CLOSE & ASSESS
Exit Activity
(20 minutes) Have band students
®
AP Science Practice Check Your Understanding bring in their instruments to demon-
Examine the Concept Apply the Concept strate how vibrations work with
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
▶ ▶The amplitude of a sound wave determines our perception of ▶ ▶Imagine you are attending a symphonic concert. Explain the different instruments. Ask them 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. following questions:
their frequency and the ____________ (higher/lower) their pitch.
Copyright © Bedford, Freeman & Worth Publishers.
Answers to the Examine the Concept questions can be found in Appendix C at the end of the book. • What produces the vibrations in
each instrument?
• How does the instrument produce
Module 1.6c REVIEW louder and softer sounds?

1.6-9 What are the characteristics of air pressure tiny hair cells, triggering neural messages to be sent (via In small groups, ask students to trace
waves that we hear as sound? the thalamus) to the auditory cortex in the brain. the path of these sounds from sound
• Sensorineural hearing loss (or nerve deafness) results from waves into the nerve impulse that the
• 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- brain interprets. (Hint: Have them use
• Sound waves vary in amplitude, which we perceive as chanical system that transmits sound waves to the cochlea. Figure 1.6-18 as a guide.)
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 CLOSE & ASSESS
pitch, and locate sounds?
1.6-10 How does the ear transform sound energy Exit Assessment
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. (10 minutes) Give each student an
• The middle ear is the chamber between the eardrum and • Place theory (place coding) explains how we hear high- index card and ask them to write a
the cochlea. pitched sounds, and frequency theory (temporal coding), postcard to their parents explaining
• The inner ear consists of the cochlea, semicircular canals, extended by volley theory, explains how we hear low- one main concept they learned from
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. this module that they did not know
tiny vibrations in the eardrum. The bones of the middle ear • Sound waves strike one ear sooner and more intensely before. Before students take the index
amplify these vibrations and relay them to the fluid-filled than the other. The brain analyzes the minute differences cards home, check for misconcep-
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. tions or confusion. Remember: Take
time to address any misinformation
Sensation: Hearing Module 1.6c 141
that comes up in this assessment
activity.

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Sensation: Hearing Module 1.6c 141

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