hearing balance

7/27/2019 Hearing Balance

1/11

Physiology and Biophysics of

Auditory and Vestibular function

Dr. Charles CapadayProfessor & DirectorBrain and Movement Laboratory

CRULRG, F-65002601 de la Canardiere, Qubec City (QC),

G1J 2G3, Canadahttp://www.BrainAndMovementLab.org/
http://www.brainandmovementlab.org/http://www.brainandmovementlab.org/http://www.brainandmovementlab.org/http://www.brainandmovementlab.org/http://www.brainandmovementlab.org/


2/11

The sensitivity of the ear is remarkable.

Some facts:At 2-3 kHz the threshold of hearing intensity is about 10-16W/cm2.

This corresponds to a pressure variation of 2.9 x 10-4dyn/cm2, the

background atmospheric pressure is 1.013 x106dyn/cm2(101.3 kPa).

Random pressure variations due to thermal motion of air molecules is0.5 x 10-4dyn/cm2 ! The sensitivity of the ear is thus close to thetheoretical limit, being just above the thermal noise level.

At the threshold power level (10-16W/cm2) the displacement of the air

molecules is less than the size of the molecules themselves!

1 1 2

1 1 2

2

22

4

( )

It p v p v

Ii p v p v

From which it is readily apparent that only 0.1% of the soundenergy enters the water. Water is a very

good sound barrier.


3/11

The sensitivity of the ear is partly due to its mechanicalconstruction which amplifies sound pressure

The area of the eardrum is 30times larger than that of theoval window. So byArchimides principle

The ossicles act as a leversystem with a mechanicaladvantage of about 2.

The ear canal has a resonantfrequency circa 3 kHz,

amplifying the pressure by afactor of about 2.

Thus, 2 x 30 x 2 =120.However,


4/11

What we will explain

Sensitivity curve of human ear Sound Localization

-4

sin

lt= , where v is sound velocity

v

0.085 m. . 2.5 x 10 0.25

340m/s

In fact time differences of the order of 30 s can be detected,corresponding to an angle of about 3 deg.

l d

e g t s ms


5/11

Why primary afferent fibre firing rate is nonlinearlyrelated to stimulus intensity (but not always)

x 0 0.10 1000

y1 1 y2 800

y3 x( ) x0.3

0 500 10000

500

1000

Y-axis in Linear Scale

y1

y2

x

0 500 10000.01

0.1

1

10100

1 103

1 104

Y-axis in Log Scale

y1

y2

x

0 200 400 600 800 10000

5

10

Power Function with Exponent = 0.3

y3 x( )

x


6/11


7/11

The mammalian central auditory pathways (fordummies version).


8/11

A1 is tonotopically organized


9/11

Neural Mechanisms of sound localization

The medial superiorolive transforms atime code into a

place code.


10/11

The Barn Owls Story


11/11

A measured behaviour and its underlyingneural systems

See, T. Carew. Behavioural Neurobiology. Sinauer Associates, 2000.

hearing balance

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