hearing & deafness (4) pitch perception 1. pitch of …2 pitch of pure tones place theory place...
TRANSCRIPT
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Hearing & Deafness (4)Pitch Perception
1. Pitch of pure tones
2. Pitch of complex tones
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Pitch of pure tones
Place theoryPlace of maximum in basilar membrane excitation(excitation pattern) - which fibers excited
Timing theoryTemporal pattern of firing -how are the fibers firing -needs phase locking
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Phase-locking
-1
-0.5
0
0.5
1
0 0.2 0.4 0.6 0.8 1
Inter-spike IntervalsResponse to Low Frequency tones
time (t)
Response to High Frequency tones > 5kHz
Random intervals
time (t)
2 periods 1 periodnerve spike
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Pure tones: place vs timingLow frequency tones
Place & timing
High frequency tones
Place only
1. Phase locking only for tones below 4 kHz
2. Frequency difference threshold increases rapidlyabove 4 kHz.
3. Musical pitch absent above 4 kHz (top of piano)
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Frequencythresholdsincrease
above 4 kHz
B C J Moore (1973)JASA.
Phase-lock?Yes No
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Pitch of complex tones:fundamental & harmonics
time (t)
pres
sure
-4-3-2-1
01234
1
Period = 1/200 s = 5msfrequency (Hz)
ampl
itude
200
1.0
400 600 800
Harmonic spacing = 200 Hz
Fundamental =200 Hz
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Helmholtz’s place theory
frequency (Hz)
amp
litu
de
200
1.0
400 600 800
Harmonic spacing = 200 Hz
Fundamental =200 Hz
Pitch = frequency of fundamentalCoded by place of excitation
Peaks in excitation
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Arguments against Helmholtz
1. Fundamental not necessary for pitch(Seebeck)
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Missing fundamental
time (t)
pre
ssur
e
-3
-2
-1
0
1
2
3
1
Period = 1/200 s = 5ms frequency (Hz)
ampl
itude
200
1.0
400 600 800
Harmonic spacing = 200 Hz
No fundamental but you still hear the pitch at 200 HzTrack 37
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Distortion: Helmholtz fights back
frequency (Hz)
amp
litu
de
200
1.0
400 600 800
Harmonic spacing = 200 Hz
Sound stimulus
frequency (Hz)
amp
litu
de
200
1.0
400 600 800
Harmonic spacing = 200 Hz
Fundamental =200 Hz
Middle-eardistortion
Producesf2 - f1
600 - 400
Sound going into cochlea
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Against Helmholtz: Masking thefundamental
frequency (Hz)
amp
litu
de
200
1.0
400 600 800
Harmonic spacing = 200 Hz
Fundamental =200 Hz
Unmasked complex still has a pitch of 200 Hz
Tracks 40-42
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200 850 1050 1250
200
amp
Against Helmholtz:Enharmonic sounds
Middle-ear distortiongives difference tone(1050 - 850 = 200)
BUT
Pitch heard isactually about 210
Tracks 38-39
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Schouten’s theory
Excitation pattern of complex tone on bm
-5.0
0.0
5.0
10.0
15.0
20.0
25.0
b m
vib
rati
on
base apexlog (ish) frequency
2004001600
resolvedunresolved
600800
Output of 1600 Hz filter Output of 200 Hz filter
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 0.2 0.4 0.6 0.8 1
1/200s = 5ms
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1
1/200s = 5ms
Pitch due tobeats ofunresolvedharmonics
Tracks 43-45
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Problems with Schouten’s theory (1)1. Resolved harmonics dominant in pitch perception -not unresolved (Plomp, 1967)
“down”
frequency (Hz)200
1.0
400 600 800 2000 2400
“down”
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Problems with Schouten (2)2. Pitch discrimination much worse for unresolved than
resolved (Houtsma & Smurzynski (1990, JASA).res --> unres
good
bad
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Problems with Schouten (3)
3. Musical pitch is weak for complexsounds consisting only of unresolvedharmonics (Houtsma, 1984, MusicPerception)
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Against Schouten (4):Dichotic harmonics
• Pitch of complex tone still heard withone harmonic to each ear(Houtsma & Goldstein, 1972)
400 600
200 Hzpitch
No chance of distortion tones or physical beats
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Goldstein’s theory
• Pitch based on resolved harmonics• Brain estimates frequencies of resolved harmonics
(eg 402 597 806) - could be by a placemechanism, but more likely through phase-lockedtiming information.
• Then finds the best-fitting consecutive harmonicseries to those numbers (eg 401 602 804) -> pitchof 200.5
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Two pitch mechanisms ?
• Goldstein has difficulty with the fact thatunresolved harmonics have a pitch at all.
• So: Goldstein’s mechanism could be goodas the main pitch mechanism
• With Schouten’s being a separate (weaker)mechanism for unresolved harmonics
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Schouten’s + Goldstein's theories
-5.0
0.0
5.0
10.0
15.0
20.0
25.0
base apexlog (ish) frequency
2004001600
resolvedunresolved
600800
Output of 1600 Hz filter Output of 200 Hz filter
-2
-1.5-1
-0.5
0
0.5
11.5
2
0 0.2 0.4 0.6 0.8 1
1/200s = 5ms
-1
-0.8-0.6-0.4-0.2
00.20.40.60.8
1
0 0.2 0.4 0.6 0.8 1
1/200s = 5ms
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Some other sounds that givepitch
• SAM Noise: envelope timing - not spectral– Sinusoidally amplitude modulated noise
• Rippled noise - envelope timing & spectral– Comb-filter (f(t) + f(t-T)) -> sinusoidal spectrum– Huygens @ the steps from a fountain– Quetzal @ Chichen Itza
• Binaural interactions
100 200
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Huygen’s repetition pitch
Christian Huygens in 1693 noted that the noise produced by afountain at the chateau of Chantilly de la Cour was reflected by astone staircase in such a way that it produced a musical tone. Hecorrectly deduced that this was due to the successively longer timeintervals taken for the reflections from each step to reach thelistener's ear.
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Effect of SNHL
• Wider bandwidths, so fewer resolvedharmonics
• Therefore more reliance on Schouten'smechanism - less musical pitch?
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Problem we haven’t addressed
• What happens when you have twosimultaneous pitches - as with two voices ortwo instruments - or just two notes on apiano?
• How do you know which harmonic is fromwhich pitch?