Download CHAPTER 11: SOUND, THE AUDITORY SYSTEM, AND PITCH

CHAPTER 11: SOUND, THE AUDITORY
SYSTEM, AND PITCH PERCEPTION
1. Decibel Scale
2. Loudness Scaling
3. Tone Height and Tone Chroma
4. Periodicity Pitch: Eliminating the Fundamental and Lower Harmonics
5. Periodicity Pitch: St. Martin Chimes with Harmonics Removed
6. Frequency Response of the Ear
7. Harmonics of a Gong
8. Effect of Harmonics on Timbre
9. Timbre of a Piano Tone Played Backward
10. Cochlear Mechanics: Cilia Movement
11. Cochlear Mechanics: Traveling Waves
12. Masking High and Low Frequencies
13. Cochlear Mechanics: Cochlear Amplifier
14. Hearing Loss
15. Cochlear Implant: Environmental Sounds
16. Cochlear Implant: Music
17. Cochlear Implant: Speech
Chapter 11: Sound, The Auditory System, and Pitch Perception
1. Decibel Scale
The intensity of a sound stimulus is a function of its sound pressure level. To use sound pressure
level in its basic form, however, is not very feasible because of the range involved. To solve this
problem, a scale that is more compressed is used: the decibel (dB). The formula for dB is dB =
20log(p/p0), where p = the sound pressure level of the stimulus, and p0 = a standard sound
pressure level. The standard sound pressure level is approximately the absolute threshold at
1000 Hz.
Because the dB scale is logarithmic, large increases in the pressure ratio result in relatively small
increases in the dB SPL; for example, multiplying the pressure ratio by 10 increases dB by 20
dB, so, a change from 20 dB to 40 dB represents a change in the pressure ratio from 10 to 100,
but a change from 120 dB to 140 dB occurs when the pressure ratio increases from 1 million to
10 million.
In this exercise you will hear the magnitude of change associated with increases of 10 dB SPL.
For each pair of tones, the second tone will be 10 dB louder than the first. Notice whether you
can hear both tones in each of the pairs and whether the increase in loudness is the same for all
pairs.
RESULTS & DISCUSSION
1. Were you able to hear both tones in all five pairs of tones? Why might some people not hear
all the tones?
2. The second tone in each pair was 10 dB greater than the first tone. Did the change in
loudness sound the same across all five pairs of tones? What does this suggest?
Virtual Lab Manual
327
Chapter 11: Sound, The Auditory System, and Pitch Perception
2. Loudness Scaling
Stevens’ magnitude estimation procedure has commonly been used to map the relationship
between physical intensity and loudness. In this procedure, observers assign a loudness rating to
sounds of different physical intensities. Observers are initially presented a standard stimulus and
told the rating it should be assigned, and subsequent stimuli are rated relative to that standard.
By plotting the rating as a function of the physical intensity, the relationship between loudness
and intensity may be identified. One commonly cited result of such rating experiments is that an
increase of 10 dB results in a perceived doubling of loudness.
In this exercise, you will carry out a magnitude estimation procedure like that described above.
Create a matrix like the one shown in the exercise. Use the matrix below to record your rating
for each stimulus. Six series of stimuli will be presented. The first stimulus in each series is the
standard stimulus, so it is assigned a rating of 10 in the matrix. Record your ratings for each
stimulus as indicated in the instructions.
RESULTS & DISCUSSION
1. Report your ratings for each stimulus in the matrix below.
SERIES
1
2
3
4
5
6
STANDARD
10
10
10
10
10
10
Virtual Lab Manual
1
2
3
329
Chapter 11: Sound, The Auditory System, and Pitch Perception
(2. Loudness Scaling Cont.)
2. Using the intensity values (in dB) on the second screen plot your results in the graph below.
You should plot one data point for each entry in the matrix above.
3. Based on the function you’ve plotted, does an increase in 10 dB result in a doubling of
loudness? Is this true for the entire range of stimuli?
4. How consistent were your ratings? Did consistency vary across intensities, or did the
inconsistent ratings occur with no predictability? What do you think accounts for any
inconsistencies?
5. The sounds in this exercise consisted of a “white noise,” stimulus, which is a mixture of many
frequencies. Do you think your data would look different if pure tones were used? Would
the frequency of the tone make a difference? Why or why not?
Virtual Lab Manual
331
Chapter 11: Sound, The Auditory System, and Pitch Perception
3. Tone Height and Tone Chroma
Pitch is largely determined by the dominant frequency of a tone. As frequency increases, so does
pitch. Some pitches, those separated by an octave, sound very similar. This exercise presents
stimuli that demonstrate the concept of tone height and tone chroma. Click on each button to
hear the stimuli.
RESULTS & DISCUSSION
1. Explain what is meant by tone height. How do stimuli of differing tone heights differ
physically? How do they differ perceptually?
2. Explain what is meant by tone chroma. How are stimuli with the same tone chroma related?
How are they similar perceptually? How are they different?
Virtual Lab Manual
333
Chapter 11: Sound, The Auditory System, and Pitch Perception
4. Periodicity Pitch: Eliminating the Fundamental and Lower Harmonics
When a key on a piano is struck, the sound produced is composed of a fundamental frequency
and several harmonics. The pitch of the sound is related to the sound’s fundamental frequency.
As the sound’s fundamental frequency increases, so does its pitch.
This lab demonstrates the missing fundamental effect, or periodicity pitch. A series of five tones
are presented. The first tone contains the fundamental and all the harmonics. The fundamental
frequency has been removed from the second tone and each subsequent tone lacks one or more
higher harmonics. Listen carefully, and note any changes in your perception of the tones. The
series of tones is repeated once.
RESULTS & DISCUSSION
1. As harmonics were removed, what changed about perception of the tones?
2. As harmonics were removed, what remained the same about perception of the tones?
Virtual Lab Manual
335
Chapter 11: Sound, The Auditory System, and Pitch Perception
5. Periodicity Pitch: St. Martin Chimes with Harmonics Removed
In the previous demonstration of periodicity pitch the fundamental frequency and the lower
harmonics were removed in a systematic fashion, and pitch did not change. This lab presents the
tune played by St. Martin’s chimes. Four versions are presented. In the first version all
harmonics are included. For the second version the fundamental frequency (1st harmonic) has
been removed. For the last two versions, additional harmonics have been removed. Listen
carefully, and note any changes in the pitch or other timbre.
RESULTS & DISCUSSION
1. How did each version sound? Did pitch vary as the harmonics varied? Did other changes
occur?
2. What does this demonstration suggest about pitch perception?
Virtual Lab Manual
337
Chapter 11: Sound, The Auditory System, and Pitch Perception
6. Frequency Response of the Ear
This exercise demonstrates the variation in sensitivity across different frequencies. Before
listening to the tone series, be sure to adjust the volume to a comfortable level. After adjusting
the calibration tone’s intensity, click on Series 1. Each series contains nine tones that are equal
in physical intensity. Listen carefully, and record your data in the table below.
RESULTS & DISCUSSION
1. Enter the number of the lowest frequency, and highest frequency tones you could hear for
each series.
SERIES
LOWEST FREQUENCY TONE
HEARD (#)
HIGHEST FREQUENCY TONE
HEARD (#)
1
2
3
2. Did all of the tones in a series sound equally loud? If not, which ones sounded loudest (low
frequency, middle, high frequency)? If some tones sounded louder, explain why.
3. What does this exercise show about the relationship between physical intensity and loudness?
Virtual Lab Manual
339
Chapter 11: Sound, The Auditory System, and Pitch Perception
7. Harmonics of a Gong
In this exercise, you will hear a gong sound that contains a number of harmonics. The complex
sound will be preceded by a cue tone that has a frequency which corresponds to one of the
harmonics of the gong. Listen carefully and see if you can detect the cue tone harmonic in the
complex sound.
RESULTS & DISCUSSION
1. Describe your perception. Was it possible to hear the frequency of the cue tone when the
complex gong-tone was present?
2. Were some harmonics harder to detect than others? If so, which ones (high or low
frequency).
Virtual Lab Manual
341
Chapter 11: Sound, The Auditory System, and Pitch Perception
8. Effect of Harmonics on Timbre
This lab illustrates how adding harmonics can affect the timbre of a sound. You will hear a
series of tones. The first tone is only the fundamental frequency. Eight harmonics are added to
the fundamental frequency, one at a time, on subsequent presentations of the tone. Pay close
attention to how the sound changes as the harmonics are added.
RESULTS & DISCUSSION
1. How did the sound change as harmonics were added?
2. What general conclusion might we make concerning the influence of having multiple
harmonics?
3. Did pitch change as harmonics were added? Explain this.
Virtual Lab Manual
343
Chapter 11: Sound, The Auditory System, and Pitch Perception
9. Timbre of a Piano Tone Played Backwards
The previous lab demonstrated that the harmonic components of a tone affect timbre. The
specific harmonics are not the only determinant of timbre, however. The timing of a tone’s
attack and decay also greatly influence timbre. Attack is the buildup of the sound at the
beginning of the tone. Decay is the decrease in the sound at the end of the tone. The speed of
attack and decay influences the “sound envelope,” the “shape” of the sound, and the nature of the
sound envelope is important in timbre.
This lab demonstrates how changing the attack and decay may affect the characteristics of
sounds. You will hear two versions of a composition played on the piano. In the first, the piece
is played normally. Pay attention to the timbre of the piano. In the second, the notes are in the
same order as the original piece, but, instead of the beginning of each note coming first, the end
of the sound is heard first. Again, note the timbre. Be sure you understand how the versions
differ.
RESULTS & DISCUSSION
1. Compare the characteristics of each version of the music. Did timbre vary?
2. Did the pitch change when the sounds were reversed? Was the melody the same?
3. Why does the second version sound so different? (Don’t just say, “The sounds are played
backwards.” Give specific reasons, using the characteristics of sound previously discussed.)
Virtual Lab Manual
345
Chapter 11: Sound, The Auditory System, and Pitch Perception
10. Cochlear Mechanics: Cilia Movement
This animation shows how the cilia that sit on top of the hair cell move in response to a sound
stimulus. The hair cell is activated when the cilia move to the right, and is not activated as the
cilia move back to the left.
Demonstration courtesy of Stephen T. Neely.
Virtual Lab Manual
347
Chapter 11: Sound, The Auditory System, and Pitch Perception
11. Cochlear Mechanics: Traveling Waves
This animation shows how the basilar membrane vibrates in response to two sound frequencies.
Demonstration courtesy of Stephen T. Neely.
RESULTS & DISCUSSION
1. Which frequency caused the largest deflection at the apex (far end) of the basilar membrane?
Virtual Lab Manual
349
Chapter 11: Sound, The Auditory System, and Pitch Perception
12. Masking High and Low Frequencies
Masking occurs when the presence of a one stimulus reduces the observer’s ability to perceive or
process another stimulus. Masking is not surprising if the two stimuli physically overlap, but
masking also can occur when the mask and target stimulus do not overlap.
As your text points out, the results of auditory masking studies provides support for the place
theory of pitch discrimination. Research shows that the effect of masking varies with the
frequency of the target tone relative to the masking tone. The movement patterns for the basilar
membrane are consistent with this masking effect, and thus, the masking data are interpreted as
evidence for the place theory.
This exercise demonstrates the auditory masking effect found in the research described above. A
600 Hz mask is always used, but the test tone is either 1,000 Hz or 200 Hz. The test tone will be
presented three times during each masking tone. This will be repeated several times, with the
intensity of the test tone decreased on each subsequent trial. Count the number of the trials on
which you are able to detect all three presentations of the 1000 Hz test tone. Repeat for the 200
Hz test tone. Use headphones, if possible, but be sure to adjust the volume to a comfortable
level.
1. Report your observations for each stimulus condition. Was there any difference in the
absolute threshold for the masked test tone in the two masking conditions?
2. Explain why this phenomenon, coupled with the basilar membrane data, support the place
theory of pitch perception.
Virtual Lab Manual
351
Chapter 11: Sound, The Auditory System, and Pitch Perception
13. Cochlear Mechanics: Cochlear Amplifier
The outer hair cells (OHC) change their length as the basilar membrane vibrates, and this length
change amplifies the basilar membrane’s movement by pushing and pulling on it. This “cochlear
amplifier” function of the OHCs is illustrated in these animations.
Demonstration courtesy of Steven T. Neely
RESULTS & DISCUSSION
Click on ”Organ Of Corti Vibration: No Cochlear Amplifier”. The tectorial membrane (green)
and the basilar membrane (brown) are vibrating, but the length of the OHCs is not changing, so
there is no cochlear amplifier effect.
Click on “Organ Of Corti Vibration: Cochlear Amplifier”. The hair cells are changing in length,
so there is a cochlear amplifier effect. Note that, although the bases of the OHCs are not shown
as contacting the basilar membrane, supporting tissue in the Organ of Corti (which is not shown
here) fills in the space. Thus, the force created as the hair cells change length can be transmitted
to the basilar membrane.
RESULTS & DISCUSSION
1. In which condition is there more vibration? Describe which parts of the Organ of Corti
vibrate more and how that would affect firing of the inner hair cells.
Virtual Lab Manual
353
Chapter 11: Sound, The Auditory System, and Pitch Perception
14. Hearing Loss
Hearing loss is estimated to affect over 28 million Americans. It can result from various causes
including excessive noise, ageing, disease, and congenital or heredity conditions. Hearing loss
can diminish one’s ability to detect sounds overall or it may be selective, affecting the ability to
hear only certain frequencies of sound. Mild to moderate levels of hearing loss can affect the
perception of many sounds that are common in our daily life and may affect them differently.
One effect of hearing loss that has the greatest impact on hearing impaired individuals is trouble
understanding others’ speech.
In this lab, you will be able to listen to various sounds as they would be perceived by a listener
with normal hearing, a listener with mild hearing loss equivalent to the high-frequency hearing
loss experienced due to normal aging by most men age 60, and a listener experiencing moderate
hearing loss in which there is further loss of high-frequency hearing.
Demonstration courtesy of Phonak, Inc.
RESULTS & DISCUSSION
1. Begin by clicking on Single Speaker, Normal Hearing. Set the volume so you can hear the
person talking clearly and easily. Keeping the volume the same, click on Single Speaker, Mild
Hearing Loss and Moderate Hearing Loss. Describe what happens.
2. Keeping the volume the same, click on Moderate Hearing Loss, Dialogue Two Speakers.
Describe what the people are talking about.
3. Click on Moderate Hearing Loss, In a Restaurant. What are the people saying?
Virtual Lab Manual
355
Chapter 11: Sound, The Auditory System, and Pitch Perception
(14. Hearing Loss, Cont.)
4. Click on Normal Hearing, In a Restaurant. Based on the knowledge of how the conversation
is perceived by a person with normal hearing, how would you describe the changes that
occurred for the hearing loss in #3?
5. How would you describe the effect of background noise on hearing when there is hearing
loss?
6. Click on a few of the other sounds. Then compare the effect of hearing loss for speech to that
for environmental sounds and music.
Virtual Lab Manual
357
Chapter 11: Sound, The Auditory System, and Pitch Perception
15. Cochlear Implant: Environmental Sounds
This demonstration provides some insight into what people who use cochlear implants hear.
Most modern cochlear implant devices stimulate the cochlea with 22 electrodes that are
positioned along the length of the cochlea to stimulate sites that respond to different frequencies.
Different types of sounds are presented as they would be heard by a person with cochlear
implants with different numbers of channels: CI-1 = 1 channel; CI-4 = 4 channels, and so on.
NH indicates what a person with normal hearing would hear.
Demonstration courtesy of Sensimetrics Corporation.
RESULTS & DISCUSSION
1. Click on CI -1 for Baby Cooing. Then click on CI – 4 and so on until you reach Normal
Hearing. How would you compare the 20-channel sound to normal hearing?
2. Which sounds were more difficult to recognize with fewer channels? Was there a difference
in ease of recognition for sounds that contained a temporal pattern like the siren vs.
continuous sounds like dishes being washed or baby cooing?
Virtual Lab Manual
359
Chapter 11: Sound, The Auditory System, and Pitch Perception
16. Cochlear Implant: Music
This demonstration illustrates how musical sounds are perceived by a person with a cochlear
implant. As in the demonstration for environmental sounds, you can listen to sounds associated
with different numbers of channels and normal hearing.
Demonstration courtesy of Sensimetrics Corporation.
RESULTS & DISCUSSION
1. Click on a number of different instruments at different channel levels. Which instrument do
you think a cochlear implant user would appreciate the most? Why is this probably the case,
according to the explanation on the demonstration?
2. What is G1 music? How would you describe perception of (a) melody and (b) rhythm using
the cochlear implant?
Virtual Lab Manual
361
Chapter 11: Sound, The Auditory System, and Pitch Perception
17. Cochlear Implant: Speech
This demonstration illustrates how speech is perceived by a person with a cochlear implant. As
in the demonstration for environmental sounds, you can listen to sounds associated with different
numbers of channels and normal hearing.
Demonstration courtesy of Sensimetrics Corporation.
RESULTS & DISCUSSION
1. For sentence #1, begin with CI-1 and progress to more channels. At which channel are you
able to make out what the person is saying?
2. For sentence #2, click on CI-1. Can you make out what the person is saying? Click on CI-1
AV. You will see a person talking. Does this help you determine what the person is saying?
3. Continue to the right; (including more channels) first by just listening to the sound, then by
listening and watching the person talking. From your observations, what do you conclude
about how seeing a person talk affects the listener’s ability to understand what they are saying
under adverse hearing conditions?
Virtual Lab Manual
363