The Auditory System: From Sound Waves to Brain Activity, Slides of Human ethology

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The Auditory SystemThe

Auditory System

Audition (Hearing) †

Transduction of physical sound waves intobrain activity via the ear. „

Sound is perceptual and subjective.

†

Structure of the ear.

†

Pathways from the ear to the cortex. „

MGN (medial geniculate nucleus of the thalamus)

„

MGN (medial geniculate nucleus of the thalamus)

Physics of SoundPhysics

of Sound

F

requency

Number of cycles completed by a wave ina given amount of timea given amount of time

Low Frequency

High Frequency

Low Frequency

High Frequency

Physics of SoundPhysics

of Sound

Amplitude

Physical strength of a waveHigh Amplitude

Low Amplitude

High Amplitude

Low Amplitude

Anatomy of Auditory Perception †

Outer ear – directs sound waves to tympanicmembrane, pinna localizes sound.

†

Middle ear – amplifies the wave and transmitsit to the fluid-filled inner ear. „

Eustachian tube – equalizes pressure and protectsear from loud noise

†

Inner ear – cochlea transduces sound wavesinto neural signals.

g

Auditory Pathways

A di

i

hl

i

i

†

A

uditory receptors in cochlea exit via auditory nerve.B

i

i^

li

i

†

B

rain stem neurons at superior olive permit sound localization.S

h

f

h

h

b

i

†

S

eparate pathways for each ear up the brain stem.MGN

†

MGN

†

Auditory cortex

Attenuation Reflex

M

l

k

h

i l

†

M

uscles contract to make the ossicles more

rigid, reducing sound transmission to the innerear

protects the ear

ear – protects the ear.

†

Operates more at low frequencies.P

i

ki

hi h f

†

P

revents saturation, making high frequency sounds more discernible.M k

h

i

d

d i

i

†

M

akes speech easier to understand in a noisy

environment.

Sound Localization

I

l i

d l

†

I

nteraural time delay „

Detected at superior oliveW

k

l^

f

i

„

W

orks at low frequencies

†

Interaural intensity difference (sound

h d

shadows) „

Works at high frequencies

Pi

l

li

d

i

ll

(f

b

†

Pi

nna localizes sounds vertically (from above and below)