Rob van der Willigen ~robvdw/cnpa04/coll1/AudPerc_2007_1

Rob van der WilligenRob van der Willigenhttp://~robvdw/cnpa04/coll1/AudPerc_2007_1.ppthttp://~robvdw/cnpa04/coll1/AudPerc_2007_1.ppt

Auditory PerceptionAuditory Perception

Q ui ckTi me™ and a TI FF (LZW) decompressor are needed to see thi s pi cture. Today’s goalsToday’s goals

Outline of The Course

Introduction to the field of Auditory Perception

Understanding the physical nature of sound

Q ui ckTi me™ and a TI FF (LZW) decompressor are needed to see thi s pi cture. General Outline P1-P2 General Outline P1-P2

P1: Auditory Perception

P2: The Mammalian Auditory System

- The Problem of Audition

- The Physical Characteristics of Sound

- Mechanotransduction

- Neuroanatomical organization

Q ui ckTi me™ and a TI FF (LZW) decompressor are needed to see thi s pi cture. General Outline P3-P5General Outline P3-P5

P3-P5: Sound Localization - Neural Correlates in Birds

and Mammals- Plasticity and

Development- Coordinate

Transformation- Measuring Sound Localization

Behaviour

Q ui ckTi me™ and a TI FF (LZW) decompressor are needed to see thi s pi cture.

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

Q ui ckTi me™ and a TI FF (LZW) decompressor are needed to see thi s pi cture. AssignmentsAssignments

Individual Assignments:

Group assignments (Pairs):

- Reading (research papers)

- Writing Succinct Essays

- Write Matlab Scripts

- Write Brief Data Reports

Q ui ckTi me™ and a TI FF (LZW) decompressor are needed to see thi s pi cture. ExaminationsExaminations

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

Q ui ckTi me™ and a TI FF (LZW) decompressor are needed to see thi s pi cture. Audition (Hearing)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 John G. Neuhoff (Ecological Psychoacoustics 2004; p. 1)2004; p. 1)

Q ui ckTi me™ and a TI FF (LZW) decompressor are needed to see thi s pi cture. PsychoacousticsPsychoacoustics

Auditory Perception or Psychoacoustics is a branch of Psychophysics.

Psychophysics studies relationships between perception and physical properties of stimuli.


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.

Q ui ckTi me™ and a TI FF (LZW) decompressor are needed to see thi s pi cture. PsychoacousticsPsychoacoustics

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



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





Elevation (deg)

-40

-20

0

+20

+40

+60

The Pinna creates Sound source position dependent spectral clues.

Frequency

“EAR PRINT”


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)




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




The cochlea’s core component is the Organ of Corti, the sensory organ of hearing



Cochleardeficits cause

Sensorineural

hearing loss


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.




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




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.


Six basic

steps:



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.


“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)


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

Q ui ckTi me™ and a TI FF (LZW) decompressor are needed to see thi s pi cture. The Adequate Stimulus to Hearing

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


The Adequate Stimulus to Hearing

http://www.physics.usyd.edu.au/~gfl/Lecture/GeneralRelativity2005/

Transverse waves

Longitudinal waves

Type of waves


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)



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


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


The Mathematics of Waves

Phaseϕ ))sin()( tAtx

Phase is a relative shift in time or space

)sin()( tAtx


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.


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.


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.


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.


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



Fourier synthesis

“Saw tooth wave”



Fourier synthesis

“Square wave”



Fourier synthesis

“Pulse train wave”



Transfer from time to frequency domain Time

domain

Superposition

Frequency domain

Fourier Analysis



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


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


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


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


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


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


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


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.


20/04/23 Joseph Dodds 2006 53


“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)


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

Rob van der Willigen ~robvdw/cnpa04/coll1/AudPerc_2007_1

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