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The Stimulus Input: Sound Waves
CONNECT 1.6-9
Point out to students that audition and
vision use similar terms to discuss the
different stimuli that are processed.
This is because both auditory and
visual stimuli work in waves, so the
characteristics of the waves are
similar. (For more on light waves, see
Module 1.6b.)
• Wavelength determines the quality
of the waves (for sound, pitch; for
vision, color).
• Amplitude determines the intensity
of the waves (for sound, loudness;
for vision, brightness).
Copyright © Bedford, Freeman & Worth Publishers.
ENGAGE 1.6-9
(Out of class) Have students measure
the decibels of different sounds com-
mon to school—for example, the bells
that signal class changes, hall noise,
and different teachers’ voices. (Hint:
There are free apps to do this.) Do
these sounds fall within the safe range
of decibels described in the textbook?
Distributed by Bedford, Freeman &
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136 Unit 1 Biological Bases of Behavior
03_HammerTE4e_47547_ch01_2a_163_4pp.indd 136
AP Exam Tip 1.6-9 What are the characteristics of air pressure waves that we hear as sound?
e the characteristics of air pr
What ar
®
1.6-9
essur
e waves that we hear as sound?
Both light and sound travel in Like light waves, sound waves vary in shape ( Figure 1.6-17 ). The height, or amplitude, of
waves. In each case, under- sound waves determines their perceived loudness. Their frequency (measured in hertz )
standing the meaning of varying
determines the pitch we experience. Long waves have low frequency — and low pitch.
amplitude and length of the waves Short waves have high frequency — and high pitch. The sound waves produced by a violin
®
is important for the AP exam.
are much shorter and faster than those produced by a cello or a bass guitar.
We measure sound intensity in decibels, with zero decibels representing the absolute
frequency the number of threshold for hearing. Every 10 decibels correspond to a tenfold increase in sound intensity.
complete wavelengths that Thus, normal conversation (60 decibels) is 10,000 times more intense than a 20-decibel whis-
pass a point in a given time (for per. And a temporarily tolerable 100-decibel passing subway train is 10 billion times more
example, per second).
pitch a tone’s experienced intense than the faintest detectable sound. If prolonged, exposure to sounds above 85 decibels
highness or lowness; depends on can produce hearing loss. Tell that to basketball fans at the University of Kentucky who,
frequency. in 2017, broke the Guinness World Record for the noisiest indoor stadium at 126 decibels
( WKYT, 2017 ). Hear today, gone tomorrow.
Figure 1.6-17 Short wavelength = high frequency Great amplitude
(loud sounds)
(high-pitched sounds)
The physical properties of
waves
(a) Waves vary in wavelength (the
distance between successive
peaks). Frequency, the number
of complete wavelengths that
can pass a point in a given time, Long wavelength = low frequency Small amplitude
depends on the wavelength. (low-pitched sounds) (soft sounds)
The shorter the wavelength, the
higher the frequency. Wavelength
determines the pitch of sound.
(b) Waves also vary in amplitude
(the height from peak to trough). (a) (b)
Wave amplitude influences sound
intensity.
lower pitch. Differences in the waves’ Worth Publishers. Not for redistribution.
The sounds of music A violin’s
short, fast waves create a high pitch.
The longer, slower waves of Chi-chi
Nwanoku Obe ’ s double bass create a
height, or amplitude, also create
Vereshchagin Dmitry/Shutterstock Courtesy of Eric Richmond/The Chineke! Foundation
differing degrees of loudness.
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