Simulating and Measuring Otoacoustic Emissions - Cecilia Casarini

SIMULATINGAND

MEASURINGOTOACOUSTICEMISSIONS

Cecilia Casarini

Outline

Physiology of theear

Outer Ear

Middle Ear

Inner Ear

OtoacousticEmissions

Cochlear Model

Simulations

Measurements

Conclusions

SIMULATING AND MEASURINGOTOACOUSTIC EMISSIONS

Cecilia Casarini

Master of ScienceAcoustics and Music Technology (MSc)

University of Edinburgh

23rd August, 2016

SIMULATINGAND


Cecilia Casarini

Outline


Outer Ear

Middle Ear

Inner Ear


Cochlear Model

Simulations

Measurements

Conclusions

OUTLINE

1 Physiology of the earOuter EarMiddle EarInner Ear

2 Otoacoustic Emissions

3 Cochlear Model

4 Simulations

5 Measurements

6 Conclusions

SIMULATINGAND


Cecilia Casarini

Outline


Outer Ear

Middle Ear

Inner Ear


Cochlear Model

Simulations

Measurements

Conclusions

Physiology of the ear - OUTER EAR

Pinna (or Auricula):receives sounds from anydirection, responsible ofsound localization.

Ear canal: 2.5 cm long.

Resonant frequencies

f (n) = (2n − 1)cs4l

Eardrum (or tympanicmembrane): vibrates whenpressure wave enters the earcanal

SIMULATINGAND


Cecilia Casarini

Outline


Outer Ear

Middle Ear

Inner Ear


Cochlear Model

Simulations

Measurements

Conclusions

Physiology of the ear - MIDDLE EAR

Impedance matching between airand fluid to avoid reflection:

Pressure Amplification

Resonant frequencies

Aeardrum

Astapes=

Peardrum

Pstapes= 18.75

Lever action of middle earbones, increasing amplitudeand decreasing velocity,gain= 4.4

Total gain = 4.4 ∗ 18.75 = 82.5

SIMULATINGAND


Cecilia Casarini

Outline


Outer Ear

Middle Ear

Inner Ear


Cochlear Model

Simulations

Measurements

Conclusions

Physiology of the ear: INNER EAR

Two main functions:

Tonotopy

Active feedback:compressive, non linear

SIMULATINGAND


Cecilia Casarini

Outline


Outer Ear

Middle Ear

Inner Ear


Cochlear Model

Simulations

Measurements

Conclusions

OTOACOUSTIC EMISSIONS

Stimulus-based classification:

SOAEs (spontaneous)

SFOAEs (stimuls-frequency)

TEOAEs (transient-evoked)

DPOAEs(distortion-product)

Generation-based classification:

Linear reflection

Nonlinear distortion

SIMULATINGAND


Cecilia Casarini

Outline


Outer Ear

Middle Ear

Inner Ear


Cochlear Model

Simulations

Measurements

Conclusions

COCHLEAR MODEL

Three examples of cochlear models:

Neely and Kim (1986): Cochlear Model in the Frequency domain

Elliott (2007): State-space formulation in time domain

Moleti (2009): 1DOF state-space model that also simulatesotoacoustic emissions

Main assumptions:

1 The cochlea is uncurled and modelled as 1D rectangular box(macromechanics)

2 The cochlea is divided in N partitions of independent oscillators(micromechanics)

SIMULATINGAND


Cecilia Casarini

Outline


Outer Ear

Middle Ear

Inner Ear


Cochlear Model

Simulations

Measurements

Conclusions

COCHLEAR MODEL

1) 1D transmission line equation for the differential pressure p

∂2pd(x , ω)

∂2x=

2ρ

Hξ(x , t)

Using finite-difference approximation:

FP(t) = Ξ(t),F is invertible =⇒ P(t) = F−1Ξ(t)

2) Micromechanical elements

ξ(x , t) + γbm(x , ξ, ξ)ξ(x , t) + ω2bm(x , ξ, ξ)ξ(x , t) =

pd(x , 0, t)

σbm

State-space formulation:

Z (t) = AEZ (t) + BE (P(t) + S(t))

Ξ(t) = CEZ (t) =⇒ P(t) = F−1Ξ(t) = F−1CE Z (t)

SIMULATINGAND


Cecilia Casarini

Outline


Outer Ear

Middle Ear

Inner Ear


Cochlear Model

Simulations

Measurements

Conclusions

COCHLEAR MODEL

Overall state-space equation

MZ (t) = AEZ (t) + BES(t),

where M is the mass matrix of the system:

M = I − BEF−1CE

The mass matrix can be changed in:

Nonlinearity

M = I − BEG (Z )F−1CE ,where:

G (Z ) = B−1C + I

The parameter α determines the nonlinearity of the system:

α(x , ξ, t) = α0

[1− tanh

(1√λπ

∫ L

0

e−(x−x′)2/λ ξ

2(x ′, t)

ξ2satdx ′

)]

SIMULATINGAND


Cecilia Casarini

Outline


Outer Ear

Middle Ear

Inner Ear


Cochlear Model

Simulations

Measurements

Conclusions

Simulations - TONOTOPY

The basilar membrane has apeak in the cochlear placecorresponding to each inputfrequency

Video Animation of BMmotion

SIMULATINGAND


Cecilia Casarini

Outline


Outer Ear

Middle Ear

Inner Ear


Cochlear Model

Simulations

Measurements

Conclusions

Simulations - NONLINEAR vs LINEAR

Saturation of the nonlinear active mechanism vs linear case:

α = 0.75 α = 0

SIMULATINGAND


Cecilia Casarini

Outline


Outer Ear

Middle Ear

Inner Ear


Cochlear Model

Simulations

Measurements

Conclusions

Simulations - TEOAEs

SIMULATINGAND


Cecilia Casarini

Outline


Outer Ear

Middle Ear

Inner Ear


Cochlear Model

Simulations

Measurements

Conclusions

Simulations - DPOAEs

SIMULATINGAND


Cecilia Casarini

Outline


Outer Ear

Middle Ear

Inner Ear


Cochlear Model

Simulations

Measurements

Conclusions

Measurements

SIMULATINGAND


Cecilia Casarini

Outline


Outer Ear

Middle Ear

Inner Ear


Cochlear Model

Simulations

Measurements

Conclusions

Measurements - TEOAEs

SIMULATINGAND


Cecilia Casarini

Outline


Outer Ear

Middle Ear

Inner Ear


Cochlear Model

Simulations

Measurements

Conclusions

Measurements - DPOAEs

SIMULATINGAND


Cecilia Casarini

Outline


Outer Ear

Middle Ear

Inner Ear


Cochlear Model

Simulations

Measurements

Conclusions

Measurements - DPOAEs(Model vs Experimental measurements)

SIMULATINGAND


Cecilia Casarini

Outline


Outer Ear

Middle Ear

Inner Ear


Cochlear Model

Simulations

Measurements

Conclusions

Measurements - DPOEAEs(emissions not detected)

SIMULATINGAND


Cecilia Casarini

Outline


Outer Ear

Middle Ear

Inner Ear


Cochlear Model

Simulations

Measurements

Conclusions

Conclusions

Physical Model of the Cochlea:

Strong Linear and Nonlinear Models

Can simulate TEOAEs and DPOAEs

However:

We need a faster model

We should simulate also SOAEs

Work on Latency

Measurements:

Successfully measured DPOAEs

However:

We need a stronger analysis method for TEOAEs and SOAEs

Do more experiments in order to have reliable results and in thefuture substitute audiograms with OAEs screening tests.

SIMULATINGAND


Cecilia Casarini

Outline


Outer Ear

Middle Ear

Inner Ear


Cochlear Model

Simulations

Measurements

Conclusions

THANK YOU!

Simulating and Measuring Otoacoustic Emissions - Cecilia Casarini

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