PHY2464 -The Physical Basis of Music
PHY
-2464
PHY-2464
Physical Basis of Music
Presentation
Presentation 55
Human
Human Ear
Ear
Taken
Taken largely
largely from
from Sam
Sam Matteson’s
Matteson’s
Unit
2
Sessions
12
&
Unit 2 Sessions 12 & 13
13
Sam
Sam Trickey
Trickey
Jan.
Jan. 26,
26, 2005
2005
PHYPHY-2464
Pres. 5 Human Ear
Ludwig van Beethoven
(1770-1827)
9th Symphony (Choral)
Composed when he was
profoundly deaf (from 1820
onward).
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PHY2464 -The Physical Basis of Music
PHYPHY-2464
Pres. 5 Human Ear
The ear is a highly sensitive sound receptor in which
• outer ear pressure fluctuations are transformed into
• vibrations of small bones (the ossicles) in the middle
ear that ultimately are communicated to
• the cochlea, in the inner ear, where the vibrations are
further transformed by stereocilia (hair cells) into
• neural impulses distributed by frequency and scaled
by intensity.
PHYPHY-2464
Pres. 5 Human Ear
Anatomy of Ear
Middle Ear
Outer Ear
Inner Ear
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PHY2464 -The Physical Basis of Music
PHYPHY-2464
Pres. 5 Human Ear
Outer Ear Anatomy
Pinna – (the feather) matches ear canal to outside
world. This is the ear we see.
Meatus – ( the passageway) conducts sound into
head. This is the “ear canal”.
Tympanium – (the drum) transforms pressure
fluctuations into displacement.
PHYPHY-2464
Pres. 5 Human Ear
Outer Ear
• Pinna ——→
• Meatus ———→
←— Tympanium
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PHY2464 -The Physical Basis of Music
PHYPHY-2464
Pres. 5 Human Ear
Anatomy of Ear
Middle Ear
PHYPHY-2464
Pres. 5 Human Ear
Middle Ear Anatomy: The Ossicles (little bones)
Malleus (the hammer) - moved by Tympanium.
Incus ― (the anvil) supported by ligaments that
protect against loud percussion.
Stapes ― (the stirrup) force multiplied by 1.3
because of lever action.
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PHY2464 -The Physical Basis of Music
PHYPHY-2464
Pres. 5 Human Ear
Tympanic Membrane (Ear Drum)
micrograph
(view from inside)
←————— Tympamium
←——— Malleus and ligaments
PHYPHY-2464
Pres. 5 Human Ear
The Ossicles
Malleus ——→
←—— Incus
←—— Stapes
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PHY2464 -The Physical Basis of Music
PHYPHY-2464
Pres. 5 Human Ear
Ossicles
(Micrographs)
Malleus
Incus
Malleus Incus
Tympanium
Stapes
Stapes
PHYPHY-2464
Pres. 5 Human Ear
Anatomy of Ear
Inner Ear
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PHY2464 -The Physical Basis of Music
PHY-2464 Pres. 5 Human Ear
Inner Ear Anatomy:
Cochlea – (the Snail) converts displacement into
neural impulses
Auditory Nerve – neural impulses to brain
Semicircular canals – detect motion & orientation
PHYPHY-2464
Pres. 5 Human Ear
Inner Ear Anatomy
←—— Semicircular Canals
Oval Window
←—— Cochlea
Round Window
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PHY2464 -The Physical Basis of Music
PHYPHY-2464
Pres. 5 Human Ear
Cochlea “The Snail”
(micrograph)
•
•
o~ oval window
r~ round window
2 mm
PHYPHY-2464
Pres. 5 Human Ear
Structure of Cochlea
1. Spiral cone
2. Divided by
Basilar
Membrane
3. In on top half
4. Out on bottom
5. “Sloshing “
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PHY2464 -The Physical Basis of Music
PHYPHY-2464
Pres. 5 Human Ear
Microstructure
of Cochlea
Basilar
——————→
Membrane
Auditory Nerve → → ↑
↑
Organ of
Corti
PHY-2464 Pres. 5 Human Ear
Organ of Corti and Basilar Membrane
Vibration
Outer
←——— Hair Cells
←————— Inner Hair Cells
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PHY2464 -The Physical Basis of Music
PHYPHY-2464
Pres. 5 Human Ear
Stereocilia (Hair Cells)
PHYPHY-2464
Pres. 5 Human Ear
Outer Hair Cell in Cross Section
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PHY2464 -The Physical Basis of Music
PHYPHY-2464
Pres. 5 Human Ear
Detail of Hair Cell
(note: “hair” in geometric
sense only.)
Stereocilia
PHYPHY-2464
Pres. 5 Human Ear
Action of Hair Cell
Vibration ))))
Neurotransmitter
released
Nerve
Hair Cell
Depolarizes
Hair Cell
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PHY2464 -The Physical Basis of Music
PHYPHY-2464
Pres. 5 Human Ear
Frequency Discrimination in Cochlea
•
•
•
•
20 Hz to 20 kHz (typical in human beings)
Resonances in Basilar membrane and in Hair
Cells (HC) cause spatial separation by frequency.
Differential movement of membranes stimulate
HC.
Minimum stimulation required for response.
Inhibition of neighbors causes non-linear
response.
PHYPHY-2464
Pres. 5 Human Ear
Neuronal Decoding of Sound (Schematic)
Low Frequency
High Frequency
Frequency response
localized in Cochlea
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PHY2464 -The Physical Basis of Music
PHYPHY-2464
Pres. 5 Human Ear
Neuronal Response to Sound
• Frequency → Where? The location in the
Cochlea at which the stereocilia are stimulated.
• Intensity → How many? The number of HC that
are stimulated by the sound determines the
perceived intensity (loudness).
PHYPHY-2464
Pres. 5 Human Ear
Vorsicht! Caution!
Repeated acoustic trauma can cause permanent and
profound hearing loss or deafness.
If you have experienced temporary hearing loss due
to loud sounds you have had a warning.
Stereocilia do regenerate daily (but cannot
overcome loud sound abuse).
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PHY2464 -The Physical Basis of Music
PHYPHY-2464
Pres. 5 Human Ear
Example Damage from Extreme Acoustic Trauma
Guinea Pig Stereocilia damage (120 dB sound)
Control, not exposed
PHYPHY-2464
After Exposure
Pres. 5 Human Ear
How does Anatomy affect perception?
• Frequency response
• Loudness perception
• Phase insensitivity
• Deafness
• Disruption of “acoustic chain.”
• Nerve death.
• Remedies
• Restore chain or increase amplitude
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PHY2464 -The Physical Basis of Music
PHYPHY-2464
Pres. 5 Sound Intensity Levels
Summary:
Anatomy : Outer, Middle and Inner Ear.
Function:
Outer – converts pressure fluctuations to
displacement.
Middle – amplifies displacement, protects
against loud noise.
Inner – converts displacement to neural
impulses, sorted by frequency.
PHYPHY-2464
Pres. 5 Sound Intensity Levels
Summary (concluded):
• Physiology determines function.
• No phase detection mechanism.
• Large “non-linear” range of 12 orders of
magnitude in intensity
• Three (3) orders of magnitude in frequency (20 Hz
to 20 kHz).
• Trauma (due to loud sounds) is a cause of
deafness.
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