Transcript Auditory Perception P1

Auditory Perception
Rob van der Willigen
http://~robvdw/cnpa04/coll1/AudPerc_2007_1.ppt
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Today’s goals
Outline of The Course
Introduction to the field of Auditory Perception
Understanding the physical nature of sound
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General Outline P1-P2
P1: Auditory Perception
- The Problem of Audition
- The Physical Characteristics of Sound
P2: The Mammalian Auditory System
- Mechanotransduction
- Neuroanatomical organization
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General Outline P3-P5
P3-P5: Sound Localization
- Neural Correlates in Birds and Mammals
- Plasticity and Development
- Coordinate Transformation
- Measuring Sound Localization Behaviour
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General Outline P6-P10
P6-P10: Perceptual Dimensions of Hearing
- Psychophysics: Measuring Perception
- Perception of Sound Level & Loudness
- Masking & Critical Band
- Illusions & Scene Analysis
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Assignments
Individual Assignments:
- Reading (research papers)
- Writing Succinct Essays
Group assignments (Pairs):
- Write Matlab Scripts
- Write Brief Data Reports
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Examinations
Students must complete all assignments
with a satisfactory record.
All assignments must be typed and
completed within one week.
Grading will occur within one week.
Students will take a written, final exam
with open, closed book questions.
P1: Psychology of Hearing
Rob van der Willigen
http://~robvdw/cnpa04/coll1/AudPerc_2007_1.ppt
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Audition (Hearing)
“Detecting and recognizing a sound
are the result of a complex interaction
of physics, physiology, sensation,
perception and cognition.”
John G. Neuhoff (Ecological Psychoacoustics 2004; p. 1)
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Psychoacoustics
Auditory Perception or Psychoacoustics
is a branch of Psychophysics.
Psychophysics studies relationships
between perception and physical
properties of stimuli.
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Physical vs. Perceptual Dimensions
Physical Dimensions:
Fundamental measures of a physical stimulus that can be
detected with an instrument (e.g., a light meter, a sound
level meter, a spectrum analyzer, a fundamental frequency
meter, etc.).
Perceptual Dimensions:
These are the mental experiences that occur inside the
mind of the observer. These experiences are actively
created by the sensory system and brain based on an
analysis of the physical properties of the stimulus.
Perceptual dimensions can be measured, but not with a
meter. Measuring perceptual dimensions requires an
observer.
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Psychoacoustics
Psychoacoustics is the study of
subjective human perception of sounds.
Psychoacoustics can be described as
the study of the psychological
correlates of the physical parameters
of acoustics.
Acoustics is a branch of physics and is
the study of sound.
Sensory Coding and Transduction
Sensory Coding and Transduction
A Sensor Called Ear
Sensory Coding and Transduction
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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
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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
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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
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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
Sensory Coding and Transduction
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Peripheral Auditory System
The cochlea’s core
component is the
Organ of Corti, the
sensory organ of
hearing
Cochlear
deficits cause
Sensorineural
hearing loss
Sensory Coding and Transduction
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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 and Transduction
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Peripheral Auditory System
Sensory Coding and Transduction
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Peripheral Auditory System
The organ of corti is the hearing sense organ and lies on
the BM (basilar membrane)
It consists of supporting cells and hair cells
2 groups of hair cells: inner and outer hair cells
Protruding from each hair cell are hairs called stereocilia
The tectorial membrane lies above the stereocilia,
shearing motion between BM and tectorial membrane
causes stereocilia to be displaced
Sensory Coding and Transduction
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Peripheral Auditory System
The auditory nerve consists of vestibular and cochlear nerve
Cochlear nerve: the axon fibres of neurons whose cell bodies
are in the spiral ganglion of the cochlea.
Dendrites of these neurons synapse with the hair cells.
The cochlear nerve transmits hearing information from
cochlea to central nervous system.
Important findings from recording impulses in single auditory
nerve fibres are:
Spontaneous firing, frequency selectivity of fibres, phase locking.
Sensory Coding and Transduction
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Peripheral Auditory System
Six basic
steps:
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The Problem of Hearing
Now we know the sensor of the
process called hearing.
It leaves open,
however, the question
of how sound is
actually encoded at
the sensory level.
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The Problem of Hearing
“Only by being aware of how sound is
created and shaped in the world can
we know how to use it to derive the
properties of the sound-producing
events around us.”
Albert S. Bregman (Auditory scene analysis, 1999; p. 1)
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The Adequate Stimulus to Hearing
Sound is a longitudinal pressure wave:
a disturbance travelling through a medium
(air/water)
http://www.kettering.edu/~drussell/demos.html
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The Adequate Stimulus to Hearing
Duration
Compression
Particles do NOT travel,
only the disturbance
Particles oscillate back
and forth about their
equilibrium positions
Decompression
or
rarefaction
Compression
Distance from source
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/sound/u11l2a.html
The Adequate Stimulus to Hearing
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Type of waves
Transverse waves
Longitudinal waves
http://www.physics.usyd.edu.au/~gfl/Lecture/GeneralRelativity2005/
Physical Dimensions of Sound
Amplitude (A)
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High
http://www.physpharm.med.uwo.ca/courses/sensesweb/
Pressure
Amplitude
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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
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Frequency (f) ; Period (T) ; Wavelength (λ)
LOW pitched sound
Low frequency
Long wavelength
Pressure changes are slow
High
Pressure
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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
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The Pure Tone
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x
(
t
)

A
sin(
2

ft

)
• has infinite duration, but only one frequency
• is periodic and has a phase
• is known as the “harmonic function”
x
(
t
)

A
sin(

t

)
 = 2 f, is the angular frequency [rad/s]
 = is phase, t is time
The Mathematics of Waves
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Phase ()
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x(t )  A  sin(  t )
x(t )  A  sin(  t   )
Phase is a
relative shift in
time or space
The Mathematics of Waves
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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
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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
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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).
The Mathematics of Waves
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Fourier’s Theorem
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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
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Fourier’s Theorem
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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
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Fourier synthesis
“Saw tooth
wave”
The Mathematics of Waves
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Fourier synthesis
“Square
wave”
The Mathematics of Waves
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Fourier synthesis
“Pulse train
wave”
The Mathematics of Waves
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Fourier Analysis
Transfer from time to frequency domain
Time domain
Frequency domain
Superposition
Physical Dimensions of Sound
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Amplitude
- height of a cycle
- relates to loudness
Wavelength (λ)
- distance between peaks
Phase ( )
- relative position of the peaks
Frequency (f )
- cycles per second
- relates to pitch
Summary
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The Problem of Hearing
Now we know the sensor of the
transduction process called hearing.
And we know a little about the
physical nature of sound (Acoustics).
So it should be possible to
understand how sound is encoded at
the sensory level.
Sensory Coding of Sound
Outer
Hair cells
Organ of Corti
Inner
Hair cell
Auditory nerve
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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Place Theory
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
Sensory Coding of Sound
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Cochlear Fourier Analysis
Periodic stimulation
of the Basilar
membrane matches
frequency of sound
High f
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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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 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
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Perceptual Attributes of Sound
Pitch (not fundamental
frequency)
Loudness (not intensity)
Timbre (not spectrum envelope or
amplitude envelope)
The terms pitch, loudness, and timbre refer NOT to the
physical characteristics of sound.
They refer to the mental experiences that occur in the
brains of listeners.
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21/07/2015
Joseph Dodds 2006
53
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The Problem of Hearing
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“Sound has no dimensions of space,
distance, shape, or size; and the
auditory periphery of all known
vertebrates contains peripheral receptors
that code for the parameters of the
sound pressure wave rather than
information about sound sources per se.”
William A. Yost (Perceiving sounds in the real world, 2007; p.
3461)
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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 Audition
Problem I: Sound
localization can only
result from the neural
processing of acoustic
cues in the tonotopic
input of the (two) ear(s)!
Problem II: How does
the auditory system parse
the superposition of
distinct sounds into the
original acoustic input?
Periodicity of waves: time and space
Announcements
1. This week, we will have the first lab, entitled “Introduction to
harmonic waves and Fourier (Spectrum Analysis)”
2. Read the print outs.
3. Importantly, the section MATLAB PRIMER is a complementary
material for the very first lab.
4. This week’s reading assignment.
2005Syracuse University
11
The basic relation underlying all waves:
Wave-speed equals frequency times wavelength.
In symbols, v = fλ.
This equation is called the wave-relation.
Unit for wave-speed is: [v] = 1 m/s