Transcript Auditory Perception P1

Auditory Perception
Rob van der Willigen
http://~robvdw/cnpa04/coll4/AudPerc_2008_P4.ppt
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General Outline P4
P4: Auditory Perception
- Cochlear Mechanotransduction
- Neuroanatomical Organization
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Sensory Coding and Transduction
Mammalian Auditory Pathway
Cochlear Mechanotransduction
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Sensory Coding and Transduction
6 critical steps
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Physical Dimensions of Sound
Summary
x(t)  A sin( 2f  t  )
Amplitude
- height of a cycle
- relates to loudness
Wavelength (λ)
- distance between peaks
Phase (Φ)
- relative position of the peaks
Frequency (f )
- cycles per second
- relates to pitch
Recapitulation previous lectures
The Adequate Stimulus to Hearing
Summary
Sound is a longitudinal pressure wave:
a disturbance travelling through a medium
http://www.kettering.edu/~drussell/demos.html
(air/water)
Recapitulation previous lectures
The Adequate Stimulus to Hearing
Type of waves
Transverse waves
Longitudinal waves
http://www.physics.usyd.edu.au/~gfl/Lecture/GeneralRelativity2005/
The Adequate Stimulus to Hearing
Summary
Duration
Compression
Decompression
Particles do NOT travel,
only the disturbance
Particles oscillate back
and forth about their
equilibrium positions
Compression
Distance from source
Recapitulation previous lectures
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/sound/u11l2a.html
Physical Dimensions of Sound
Amplitude (A)
http://www.physpharm.med.uwo.ca/courses/sensesweb/
Pressure
Amplitude
High
LOUD sound
Large change in
amplitude
Low
SOFT sound
Small change in
amplitude
Time or Distance from the source
In air the disturbances travels with the 343 m/s,
the speed of sound
Amplitude is a measure of pressure
Physical Dimensions of Sound
Frequency (f) ; Period (T) ; Wavelength (λ)
LOW pitched sound
Low frequency
Long wavelength
Pressure changes are slow
Pressure
High
Low
HIGH pitched sound
High frequency
Short wavelength
Pressure changes are fast
One cycle
Time or Distance from source
T is the Period (duration of one cycle)
λ is wavelength (length of one cycle)
f is frequency (speed [m/s] / λ [m]) or (1/T[s])
The Mathematics of Waves
Phase ()
x(t )  A  sin(   t )
x(t )  A  sin(   t   )
Phase is a
relative shift in
time or space
The Mathematics of Waves
Fourier’s Theorem
Jean Baptiste
Fourier (1768-1830)
Any complex periodic wave can be “synthesized”
by adding its harmonics (“pure tones”) together
with the proper amplitudes and phases.
“Fourier analysis”
Time domain
“Fourier synthesis”
Frequency domain
The Mathematics of Waves
Fourier’s Theorem
Linear Superimposition of Sinusoids to build
complex waveforms

x(t )  A0   An cos( n t   n )
n 1
If periodic repeating
 n  n1
The Mathematics of Waves
Fourier synthesis
“Saw tooth
wave”
The Mathematics of Waves
Fourier synthesis
“Square
wave”
The Mathematics of Waves
Fourier synthesis
“Pulse train
wave”
The Mathematics of Waves
Fourier Analysis
Transfer from time to frequency domain
Time domain
Frequency domain
Superposition
The Mathematics of Waves
Superposition
Waves can occupy the same part of a medium
at the same time without interacting.
Waves don’t collide like particles.
Two waves (with the same
amplitude, frequency, and
wavelength) are traveling in
opposite directions.
The summed wave is no longer
a traveling wave because the
position and time dependence
have been separated.
The Mathematics of Waves
Superposition
Waves can occupy the same part of a medium
at the same time without interacting.
Waves don’t collide like particles.
Waves in-phase (=0) interfere
constructively giving twice the
amplitude of the individual
waves.
When the two waves have
opposite-phase (=0.5 cycle),
they interfere destructively and
cancel each other out.
The Mathematics of Waves
Superposition
Most sounds are the sum of many waves
(pure tones) of different Frequencies, Phases
and Amplitudes.
At the point of overlap the net amplitude is
the sum of all the separate wave amplitudes.
Summing of wave amplitudes leads to
interference.
Through Fourier analysis we can know the
sound’s amplitude spectrum (frequency content).
Sensory Coding and Transduction
Sensory Coding and Transduction
A Sensor Called Ear
Sensory Coding and Transduction
Peripheral Auditory System
Outer Ear:
- Extents up to Eardrum
- Visible part is called Pinna or
Auricle
- Movable in non-human
primates
- Sound Collection
- Sound Transformation
Gives clues for sound localization
Sensory Coding and Transduction
Peripheral Auditory System
Elevation (deg)
+60
+40
+20
0
-20
-40
Frequency
The Pinna creates
Sound source position
dependent spectral
clues.
“EAR PRINT”
Sensory Coding and Transduction
Amplitude (dB)
Peripheral Auditory System
In humans mid-frequencies
also exhibit a prominent
notch that varies in
frequency with changes
in sound source elevation
(6 – 11 kHz)
Elevation
Elevation (deg)
+60
+40
+20
0
-20
-40
Frequency kHz
Sensory Coding and Transduction
Peripheral Auditory System
Barn Owls have
Asymmetric Ears and
Silent Flight.
One ear points upwards,
the other downwards.
Sensory Coding and Transduction
Peripheral Auditory System
Middle Ear: (Conductive hearing loss)
- Mechanical transduction (Acoustic Coupling)
- Perfect design for impedance matching Fluid in inner ear is much harder to
vibrate than air
- Stapedius muscle: damps loud sounds
Three bones (Ossicles)
A small pressure on a large area (ear
drum) produces a large pressure on a
small area (oval window)
Sensory Coding and Transduction
Peripheral Auditory System
Inner Ear:
The Cochlea is the
auditory portion of
the ear
Cochlea is derived from the
Greek word kokhlias "snail
or screw" in reference to its
spiraled shape, 2 ¾ turns,
~ 3.2 cm length (Humans)
Sensory Coding and Transduction
Peripheral Auditory System
The cochlea’s core
component is the
Organ of Corti, the
sensory organ of
hearing
Cochlear
deficits cause
Sensorineural
hearing loss
Its receptors
(the hair cells)
provide the sense of hearing
Sensory Coding and Transduction
Peripheral Auditory System
The Organ of Corti
mediates
mechanotransduction:
The cochlea is filled with a
watery liquid, which moves
in response to the vibrations
coming from the middle ear
via the oval window.
As the fluid moves, thousands
of hair cells are set in motion,
and convert that motion to
electrical signals that are
communicated via
neurotransmitters to many
thousands of nerve cells.
Sensory Coding of Sound
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Cochlear anatomy
Sensory Coding of Sound
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Cochlear anatomy (straightened)
Sensory Coding of Sound
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Tonotopic coding
Pressure waves distort basilar membrane on the
way to the round window of tympanic duct:
- Location of maximum distortion varies with
frequency of sound
- Frequency information translates into information
about position along basilar membrane
Sensory Coding of Sound
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Travelling Wave Theory
Periodic stimulation of the Basilar membrane matches frequency of sound
Travelling wave theory von Bekesy: Waves move down basilar
membrane stimulation increases, peaks, and quickly tapers
Location of peak depends on frequency of the sound, lower
frequencies being further away
Sensory Coding of Sound
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Cochlear Fourier Analysis
High f
Periodic stimulation
of the Basilar
membrane matches
frequency of sound
Med f
Location of the peak
depends on
frequency of the
sound, lower
frequencies being
further away
Low f
BASE
APEX
Position along the basilar membrane
Sensory Coding of Sound
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Travelling wave
theory von Bekesy:
Waves move down
basilar membrane
Location of the peak
depends on
frequency of the
sound, lower
frequencies being
further away
Location of the peak
is determined by the
stiffness of the
membrane
Place Theory
Sensory Coding of Sound
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Sensory Input is Tonotopic
Thick & taut near base
Thin & floppy at apex
TONOTOPIC PLACE MAP
LOGARITHMIC:
20 Hz -> 200 Hz
2kH -> 20 kHz
each occupies 1/3
of the basilar membrane
Sensory Coding of Sound
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Sensory input is tonotopic
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Sensory Coding of Sound
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Sensory Input is Non-linear
The COCHLEA:
Decomposes sounds into
its frequency components
Represents sound
TONOTOPICALLY
Has direct relation to the
sounds spectral content
Has NO linear relationship
to sound pressure
Has NO direct relationship
to the sound’s location in
the outside world
Cochlear nonlinearity
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Active processing of sound
Iso-level curves show sharp
tuning at low sound levels,
broader tuning at high levels.
Effects of an “active”cochlea
Frequency (kHz)
Response is strongly
compressive around the
so-called characteristic
frequency (CF).
BM Velocity
(dB re. 1µ /s)
60
80
70
60
40
50
10
40
3
30
20
20
Requires functioning outer hair
cells.
0
1
2
3
4
5
6
7
8
9 10 11 12
The response of the BM at location most
sensitive for ~ 9 KHz tone (CF).
The level of the tone varied from 3 to 80
dB SPL (iso-intensity contours).
Cochlear nonlinearity
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Frequency (kHz)
BM Velocity
(dB re. 1µ /s)
60
80
70
60
40
50
10
40
3
30
20
20
0
1
2
3
4
5
6
7
8
9 10 11 12
Frequency [kHz]
The response of the BM at location
most sensitive for ~ 9 KHz tone (CF).
The level of the tone varied from 3 to
80 dB SPL (iso-intensity contours).
OUTPUT Response in dB
Active processing of sound
CF= 9 kHz
~4.5kHz
INPUT level (dB SPL)
BM input-output function for a tone
at CF (~9 kHz, solid line) and a tone
one octave below (~4.5 kHz) taken
from the iso-intensity contour plot.
Cochlear nonlinearity
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No nonlinearity post mortem
Rugero et al. (1997)
Basilar-membrane intensity-velocity coding functions
for a chinchilla using a tone at the 10 kHz
1) Reduced gain:
Higher thresholds in
quiet; loss of audibility
as measured with
pure-tone audiogram
2) Loss of nonlinearity:
Reduced dynamic range;
quiet sounds lost but loud
sounds just as loud:
Loudness Recruitment
GAIN equals D Amplitude of motion divided by
DAmplitude of stimulus pressure
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The Problem of Hearing
Tonotopie blijft
in het auditief
systeem tot en
met de auditieve
hersenschors
behouden.
“De samenstelling van een geluid uit afzonderlijke
tonen is te vergelijken met de manier waarop
wit licht in afzonderlijke kleuren uiteenvalt wanneer
het door een prisma gaat .”
John A.J. van Opstal (Al kijkend hoort men, 2006; p. 8)
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The Problem of Hearing
Mapping can be an important clue to the function of an area. If
neurons are arrayed according to the value of a particular
parameter, then that property might be critical in the processing
performed by that area.
Neurons within a brain area
may be organized
topographically (or in a map),
meaning that neurons that are
next to each other represent
stimuli with similar properties.
Neurons do not need to be
arranged topographically along
the dimensions of the reference
frame that they map, even if its
neurons do not form a map of
that space.
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The Problem of Hearing
Problem I: Sound localization
can only result from the neural
processing of acoustic cues in
the tonotopic input!
Problem II: How does the
auditory system parse the
superposition of distinct sounds
into the original acoustic input?
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08/04/2016
Joseph Dodds 2006
49
Sensory Coding of Sound
Summary
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Outer
Hair cells
Organ of Corti
Inner
Hair cell
Auditory nerve
Basilar Membrane
NEXT WEEK
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Cochlear Innervation & Auditory Nerve
Mechanotransduction: Step 5:
Vibration of basilar membrane causes vibration
of hair cells against Tectorial membrane (TM):
Movement displaces stereocilia/kinocilia,
opens ion channels in hair cell membranes
Rush of ions depolarizes hair cells,
which initiates the release of neurotransmitters
NEXT WEEK
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Cochlear Innervation & Auditory Nerve
Neural responses in the AN: Step 6
Information about region and intensity of
cochlear stimulation is relayed to CNS over
cochlear branch of vestibulocochlear nerve
(VIII):
Called the auditory nerve (AN):
Has sensory neurons in spiral ganglion of cochlea
Carries neural information to cochlear nuclei (CN) of
midbrain for distribution to other (more higher) brain
centers.
NEXT WEEK
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Cochlear Innervation & Auditory Nerve
Outer hair cells:
Primarily receiving
efferent inputs.
Inner hair cells:
type 1
type 2
Main source of afferent
signal in auditory nerve.
(~ 10 afferents per hair cell)
Type I neurons (95%
of all ganglion cells)
have a single ending
radially connected to
IHCs.
Type II small, unmyelinated
neurons spiral basally
after entering the organ
of Corti and branch to
connect about ten OHCs,
in the same row.
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The Auditory Nerve
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FTC versus FRC
FTC data indicate the characteristics of the cochlea from which has been eliminated
the non-linear response characteristics of the cochlear nerve excitation process.
Response Rate versus Frequency Curve
(FRC)
FRC data indicate the limits which may be set upon the central representation of
the cochlear filtering by the non-linear rate behavior of the cochlear fibers.
The Auditory Nerve
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Frequency Selectivity: CF & place theory
Place Theory:
Place of maximum vibration along
basilar membrane correlates with
the place of the Tuning curve (or
FTC=Frequency Threshold Curve)
along the frequency axis.
Shown are tuning curves measured
by finding the pure tone amplitude
that produces a criterion response
in an 8th nerve fiber (cat).
Tuning curves for four different
fibers (A-D) are shown.
Cochlear nonlinearity
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OHC motor driven by the Tectorial membrane
A virtuous loop.
Sound evoked perturbation of
the organ of Corti elicits a motile
response from outer hair cells,
which feeds back onto the organ
of Corti amplifying the basilar
membrane motion.