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Rob van der WilligenRob van der Willigenhttp://~robvdw/cnpa04/coll1/AudPerc_2007_1.ppthttp://~robvdw/cnpa04/coll1/AudPerc_2007_1.ppt
Auditory PerceptionAuditory Perception
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Outline of The Course
Introduction to the field of Auditory Perception
Understanding the physical nature of sound
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P1: Auditory Perception
P2: The Mammalian Auditory System
- The Problem of Audition
- The Physical Characteristics of Sound
- Mechanotransduction
- Neuroanatomical organization
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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-General Outline P6-P10P10
P6-P10: Perceptual Dimensions of Hearing - Psychophysics: Measuring
Perception- Perception of Sound Level &
Loudness- Masking & Critical Band
- Illusions & Scene Analysis
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Individual Assignments:
Group assignments (Pairs):
- Reading (research papers)
- Writing Succinct Essays
- Write Matlab Scripts
- Write Brief Data Reports
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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 HearingP1: Psychology of Hearing
Rob van der WilligenRob van der Willigenhttp://~robvdw/cnpa04/coll1/AudPerc_2007_1.ppthttp://~robvdw/cnpa04/coll1/AudPerc_2007_1.ppt
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“Detecting and recognizing a sound are the result of a complex interaction of physics, physiology, sensation, perception and cognition.”
John G. Neuhoff (Ecological Psychoacoustics John G. Neuhoff (Ecological Psychoacoustics 2004; p. 1)2004; p. 1)
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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 Physical vs. Perceptual DimensionsDimensions
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 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
A Sensor Called Ear
Sensory Coding and Transduction
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Peripheral Auditory Peripheral Auditory SystemSystem
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 Peripheral Auditory SystemSystem
Sensory Coding and Transduction
Elevation (deg)
-40
-20
0
+20
+40
+60
The Pinna creates Sound source position dependent spectral clues.
Frequency
“EAR PRINT”
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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 soundsThree bones (Ossicles)
A small pressure on a large area (ear drum) produces a large pressure on a small area (oval window)
Peripheral Auditory Peripheral Auditory SystemSystem
Sensory Coding and Transduction
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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
Peripheral Auditory Peripheral Auditory SystemSystem
Sensory Coding and Transduction
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The cochlea’s core component is the Organ of Corti, the sensory organ of hearing
Peripheral Auditory Peripheral Auditory SystemSystem
Sensory Coding and Transduction
Cochleardeficits cause
Sensorineural
hearing loss
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The Organ of Corti mediates mechanotransduction:
Peripheral Auditory Peripheral Auditory SystemSystem
Sensory Coding and Transduction
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.
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Peripheral Auditory Peripheral Auditory SystemSystem
Sensory Coding and Transduction
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Peripheral Auditory Peripheral Auditory SystemSystem
Sensory Coding and Transduction
The organ of corti is the hearing sense organ and lies on the BM (basilar membrane)
The tectorial membrane lies above the stereocilia, shearing motion between BM and tectorial membrane causes stereocilia to be displaced
It consists of supporting cells and hair cells2 groups of hair cells: inner and outer hair cellsProtruding from each hair cell are hairs called stereocilia
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Peripheral Auditory Peripheral Auditory SystemSystem
Sensory Coding and Transduction
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.
The cochlear nerve transmits hearing information from cochlea to central nervous system.
Dendrites of these neurons synapse with the hair cells.
Important findings from recording impulses in single auditory nerve fibres are:
Spontaneous firing, frequency selectivity of fibres, phase locking.
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Six basic
steps:
Peripheral Auditory Peripheral Auditory SystemSystem
Sensory Coding and Transduction
Q ui ckTi me™ and a TI FF (LZW) decompressor are needed to see thi s pi cture. The Problem of HearingThe 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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“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, Albert S. Bregman (Auditory scene analysis, 1999; p. 1)1999; p. 1)
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Sound is a longitudinal pressure wave: a disturbance travelling through a medium (air/water)
The Adequate Stimulus to Hearing
http://www.kettering.edu/~drussell/demos.html
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http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/sound/u11l2a.html
Particles do NOT travel, only the disturbanceParticles oscillate back and forth about their equilibrium positions
Compression
Decompression or rarefaction
CompressionDistance from source
Duratio
n
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The Adequate Stimulus to Hearing
http://www.physics.usyd.edu.au/~gfl/Lecture/GeneralRelativity2005/
Transverse waves
Longitudinal waves
Type of waves
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Physical Dimensions of Sound
http://www.physpharm.med.uwo.ca/courses/sensesweb/
Time or Distance from the source
Pressur
e
High
Low
LOUD soundLarge change in amplitude
SOFT soundSmall change in amplitude
In air the disturbances travels with the 343 m/s, the speed of soundAmplitude is a measure of pressure
Amplitud
eAmplitude
(A)
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Physical Dimensions of Sound
Time or Distance from source
Pressur
e
High
Low
LOW pitched soundLow frequency Long wavelengthPressure changes are slow
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])
HIGH pitched soundHigh frequencyShort wavelengthPressure changes are fast
Frequency (f) ; Period (T) ; Wavelength (λ)
One cycle
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The Mathematics of WavesThe Pure Tone
)2sin()( tfAtx
• has infinite duration, but only one frequency• is periodic and has a phase• is known as the “harmonic function”
x(t)Asin( t )
= 2f, is the angular frequency [rad/s]
= is phase, t is time
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The Mathematics of Waves
Phaseϕ ))sin()( tAtx
Phase is a relative shift in time or space
)sin()( tAtx
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The Mathematics of WavesSuperposit
ionWaves 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.
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The Mathematics of WavesSuperposit
ionWaves 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.
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The Mathematics of WavesSuperpositio
nMost sounds are the sum of many waves (pure tones) of different Frequencies, Phases and Amplitudes.
Through Fourier analysis we can know the sound’s amplitude spectrum (frequency content).
At the point of overlap the net amplitude is the sum of all the separate wave amplitudes. Summing of wave amplitudes leads to interference.
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The Mathematics of WavesFourier’s
Theorem
Time domain
Frequency domain
Jean Baptiste Fourier (1768-1830)
“Fourier synthesis”
“Fourier analysis”
Any complex periodic wave can be “synthesized” by adding its harmonics (“pure tones”) together with the proper amplitudes and phases.
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The Mathematics of WavesFourier’s
TheoremLinear Superimposition of Sinusoids to build complex waveforms
If periodic repeating
1
0 )cos()(n
nnn tAAtx ϕ
1 nn
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The Mathematics of Waves
Fourier synthesis
“Saw tooth wave”
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The Mathematics of Waves
Fourier synthesis
“Square wave”
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The Mathematics of Waves
Fourier synthesis
“Pulse train wave”
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The Mathematics of Waves
Transfer from time to frequency domain Time
domain
Superposition
Frequency domain
Fourier Analysis
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Physical Dimensions of Sound
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
Q ui ckTi me™ and a TI FF (LZW) decompressor are needed to see thi s pi cture. The Problem of HearingThe 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.
Organ of Corti
Basilar Membrane
Auditory nerve
Inner Hair cell
OuterHair cells
Sensory Coding of Sound
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Travelling wave theory von Bekesy: Waves move down basilar membrane stimulation increases, peaks, and quickly tapers
Periodic stimulation of the Basilar membrane matches frequency of sound
Location of peak depends on frequency of the sound, lower frequencies being further away
Sensory Coding of SoundTravelling Wave Travelling Wave
TheoryTheory
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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
Travelling wave theory von Bekesy: Waves move down basilar membrane
Sensory Coding of Sound Place TheoryPlace Theory
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High f
Med f
Low f
Periodic stimulation of the Basilar membrane matches frequency of sound
Sensory Coding of SoundCochlear Fourier Cochlear Fourier
AnalysisAnalysis
BASE APEX
Location of the peak depends on frequency of the sound, lower frequencies being further away
Position along the basilar membrane
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Thick & taut near baseThin & floppy at apex
TONOTOPIC PLACE MAP
Sensory Coding of SoundSensory Input is Sensory Input is
TonotopicTonotopic
LOGARITHMIC: 20 Hz -> 200 Hz
2kH -> 20 kHz each occupies 1/3
of the basilar membrane
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The COCHLEA:
Decomposes sounds into its frequency components
Sensory Coding of SoundSensory Input is Non-Sensory Input is Non-
linearlinear
Has direct relation to the sounds spectral content
Represents sound TONOTOPICALLY
Has NO linear relationship to sound pressureHas NO direct relationship to the sound’s location in the outside world
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Perceptual Attributes of Perceptual Attributes of SoundSound
The terms pitch, loudness, and timbre refer NOT to the physical characteristics of sound.
Pitch (not fundamental frequency)
Loudness (not intensity)
Timbre (not spectrum envelope or amplitude envelope)
They refer to the mental experiences that occur in the brains of listeners.
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20/04/23 Joseph Dodds 2006 53
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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 William A. Yost (Perceiving sounds in the real world, 2007; p. real world, 2007; p. 3461)3461)
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Tonotopie blijft in het auditief systeem tot en met de auditieve hersenschorsbehouden.
“De samenstelling van een geluid uit afzonderlijke tonen is te vergelijken met de manier waaropwit licht in afzonderlijke kleuren uiteenvalt wanneer het door een prisma gaat .”John A.J. van Opstal (Al kijkend hoort John A.J. van Opstal (Al kijkend hoort
men, 2006; p. 8)men, 2006; p. 8)
Q ui ckTi me™ and a TI FF (LZW) decompressor are needed to see thi s pi cture. The Problem of AuditionThe 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?
4
Periodicity of waves: time and spacePeriodicity of waves: time and space
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.
AnnouncementsAnnouncements
112005Syracuse University
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