Download ch7 - Physiology and Anatomy of Hearing

Communication acoustics
Ch 7: Physiology and Anatomy of Hearing
Ville Pulkki and Matti Karjalainen
Department of Signal Processing and Acoustics
Aalto University, Finland
September 14, 2016
This chapter
Structure of ear
Cochlea
Functioning of the cochlea
Cochlear non-linearities
Auditory nerve
Auditory nervous system
Structure of the ear
malleus
incus
stapes and oval window
semicircular canals
auditory nerve
cochlea
round window
Eustachian
tube
pinna
external middle inner ear
concha
eardrum
ear canal
Simplified diagram of the ear
external ear
middle ear
eardrum
inner ear
air
liquid
auditory
nerve
ear canal
ossicles
pinna
Eustachian tube
traveling wave
basilar membrane
Acoustical effect of outer ear
magnitude [dB]
20
10
0
-10
1
3
10
frequency [kHz]
Magnitude response from frontal sound source to eardrum
Middle ear: bone conduction
Ossicles
Malleus (hammer-shaped bone)
Incus (anvil-shaped bone)
Stapes (stirrup-shaped bone)
Match partially the impedance difference from air to liquid (1:3000),
malleus
incus
A1
oval window
A2
P2
P1
eardrum
oval window
stapes
eardrum
a)
b)
Middle ear conduction and features
Signal transfer function is a bandpass filter
|SVFT| [dB (ref 1 mm/s/Pa)]
−10
−15
−20
−25
−30
−35
2
10
3
10
Frequency [Hz]
4
10
Adapted from Aibara et al. (2001)
Other middle ear features
Acoustic reflex = stiffening of muscles attached to ossicles with loud
sounds
Eustachian tube, balancing air pressure between the middle ear and the
environment
Structure of the ear
malleus
incus
stapes and oval window
semicircular canals
auditory nerve
cochlea
round window
Eustachian
tube
pinna
external middle inner ear
concha
eardrum
ear canal
Inner ear, the Cochlea
Cochlea is a spiral-shaped, liquid-filled tube of about 2.7 turns and 35
mm long
Stapes vibration enters the cochlea through oval window, and exits from
round window
Basilar membrane divides the cochlea into two parts
helicotrema
bony shelf
oval
window
Reissner’s membrane
base
(basal end)
apex
(apical end)
stapes
basilar membrane
round window
Inner ear, the Cochlea
Basilar membrane between bony shelves
Division to scala vestibuli and scala tympani
Reissner’s membrane separates scala media, where higher
concentration of K+
Organ of Corti: hair cells
(shown as shaded)
Tectrorial membrane
Re
scala
media
iss
ne
tectorial
membrane
r's
m
scala vestibuli
em
br
an
e
outer
inner
hair cells
auditory nerve
bony shelf
basilar membrane
scala tympani
Hair cells
S
inner haircell
S
N
outer haircell
N
S
+
+
K
K
Hair cells
Vibration of the basilar membrane causes bending of stereocilia and
this opens ion channels which modulates potential within the cell
Activation of the cell releases neurotransmitter to synaptic junctions
between hair cell and neural fibers of the auditory nerve
A neural spike is generated that propagates in the auditory nerve fiber
Next spike possible only after at least 1 ms
Passive frequency selectivity in cochlea
Basilar membrane is nonhomogeneous transmission line
Frequencies resonate at different positions
oval
window
basilar membrane
stapes
helicotrema
liquid inertia increase
vibration
membrane mass & width increase
stiffness decrease
round
window
high f
med f
low f
Traveling wave in basilar membrane
Traveling wave has maximum vibration amplitude depending on the
frequency of wave (characteristic frequency = CF)
High frequencies resonate close to the oval window and low
frequencies close to helicotrema
amplitude
maximum
vibration of membrane
traveling
wave
direction
apex
base
basilar membrane
position
direction of liquid vibration
Active processing in cochlea
Outer hair cells actively amplify vibration at their characteristic
frequency
Effect is highest at low levels
60
velocity / pressure gain
[mm / s / Pa]
velocity [dB]
20
gain
5 & 10 dB
30
40
40
20
50
60
0
70
80
-20
0
30
60
input SPL [dB]
90
2
3 4 5 6 8 10
stimulus frequency [kHz]
Adopted from Ruggero et al. (1997)
20
Velocity of basilar membrane with different levels
Higher level causes broader excitation in frequency
Excitation spreads more towards higher frequencies
characteristic frequency [Hz]
40 dB 500 Hz sine
90 dB 500 Hz sine
326
391
464
545
636
737
850
977
1118
1276
1452
1649
1869
2114
2389
0
5
10
time [ms]
15
20 0
5
10
time [ms]
15
20
Animations
Link to cochlea anatomy animation
Link to cochlea / organ of corti animation
Auditory nerve / auditory cortex demo
Auditory nerve fibers
Several auditory nerves are connected to each inner hair cell
Auditory nerves send a spike (binary output) when they receive enough
neurotransmitter from hair cell
Different nerves are differently sensitive to level
Firing rate
[spikes/s]
80
60
(h)
40
(m)
(l)
20
0
0
20
40
60
80
Stimulus level [dB]
100
Auditory nerve fibers
Firing rate overshoot and undershoot with onset and offset of excitation
Firing rate [spikes/s]
Excitation level vs time
high
> 40
20-30
< 10
0
0
150
300
Time [ms]
450
600
Auditory nerve fibers
Response of nerves with different frequencies
Firing rate
Statistically, half-wave rectification appears
340 Hz
one cycle
Adapted from Joris et al. (1994)
670 Hz
Time
1425 Hz
2830 Hz
7100 Hz
Auditory nerve fibers
Response of nerves in cat with vowel sounds /a/ and /I/ with different
levels
Average rate shows increasing saturation with level
Frequency distribution of firing rate does not carry all information
The instantaneous temporal pattern of activation seems to carry more
information
Normalized firing rate
1.0
0.5
0.0
1.0
0.5
/I/
54dB
44dB
34dB
47dB
37dB
0.0
0.1
/a/
27dB
0.5
1.0
Characteristic frequency [Hz]
5.0
10.0
Adapted from Sachs and Young (1979)
Higher levels in processing
Eye
Ear
Cochlea
Cochlear
nucleus
SC
spatial
cues
IC
LSO
Left hemisphere
-
Right hemisphere
LSO
+
VCN
DCN
Transforming
vibrations to
neural impulses
MGB, Cortex
+
MSO
+
Preamplification,
preprocessing
L
NL
spectral
cues
Head movement
information
IC
MSO
Processing of directional
cues in left-right
dimension
Processing of spectral information
Integration of visual and auditory cues
Integration of auditory and movement
[front-back-inside resolving]
Spatial segregation of auditory events
References
These slides follow corresponding chapter in: Pulkki, V. and Karjalainen, M. Communication Acoustics:
An Introduction to Speech, Audio and Psychoacoustics. John Wiley & Sons, 2015, where also a more
complete list of references can be found.
References used in figures:
Aibara, R., Welsh, J.T., Puria, S., and Goode, R.L. (2001) Human middle-ear sound transfer function and
cochlear input impedance. Hearing Res., 152(1), 100–109.
Joris, P.X., Carney, L.H., Smith, P.H., and Yin, T. (1994) Enhancement of neural synchronization in the
anteroventral cochlear nucleus. I. responses to tones at the characteristic frequency. J. Neurophys.,
71(3), 1022–1036.
Ruggero, M.A., Rich, N.C., Recio, A., Narayan, S.S., and Robles, L. (1997) Basilar-membrane responses
to tones at the base of the chinchilla cochlea. J. Acoust. Soc. Am., 101(4), 2151–2163.
Sachs, M.B. and Young, E.D. (1979) Encoding of steady-state vowels in the auditory nerve:
Representation in terms of discharge rate. J. Acoust. Soc. Am., 66, 470–479.
Physiology and anatomy of hearing
Pulkki
Dept Signal Processing and Acoustics
23/23
September 14, 2016