Week 2 Flashcards
What are the 4 areas of the auditory system?
the
outer
ear,
the
middle
ear,
the
inner
ear
and
the
central
nervous
system. Each with different function
The ear is an energy transducer, which means?
it converts acous6c energy into
electrochemical
energy
(it
is
basically
the
translator
between
the
acous6c
world
and
the
language
that
the
brain
can
understand).
he outer ear includes?
the
pinna
and
the
auditory
canal.
It
stops
at
the
eardrum.
The canal
is
lined
with
hairs
and
secretes
“wax”
to
protect
the
ear
The
concha
of
the
pinna
and
the
auditory
canal
act
as
resonators
andund
in
certain
frequency
regions.
The
fact
that
we
have
two
ears
seace
and
the
structure
of
the
pinna
and
the
concha,
both
help
us
tospace.
What are the parts of the middle ear?
ddle
ear
includes
the
ear
drum
and
three
small
bones
known
as
the
ossicles
(hammer,
anvil,
s6rrup
or
malleus,
incus
and
stapes
in
medical
terms).
The
eardrum
(or
tympanic
membrane)
turns
air
vibra6on
into
solid
vibra6on
whichtransmiNed
through
the
ossicles
to
the
inner
ear.
The
middle
ear
structure
serves
to
amplify
the
vibra6ons
going
into
the
inner
ear.
Force difference, concha, ossicles, ear drum
When
sound
moves
the
eardrum,
the
air
within
the
closed
midrarifies,
crea6ng
sound
pressure.
This
sound
pressure
moves
tmiddle
year
and
s6mulates
the
oval
and
round
windows.
The
smoving
the
fluid
inside
the
inner
ear.
Sound
waves
apply
certain
force
to
each
square
cm
of
the
earenergy
is
transferred
to
and
concentrated
in
the
footplate
of
tmuch
smaller
than
the
eardrum.
As
a
result
of
the
size
differenmuch
greater
at
the
stapes
than
it
is
at
the
eardrum
(amplifyinThe
area
difference
between
the
ear
drum
and
the
footplate
opressure
amplifica6on
by
a
factor
of
about
15.
Combined,
this
pressure
amplifica6on
and
force
amplifica6onabout
18
dB
of
amplifica6on.
The
inner
ear
includes:
Semi-‐circular
canals
of
the
ves6bular
system,
which
is
dedbalance
and
mo6on
detec6on.
-‐ The
cochlea,
where
the
mechanical
vibra6ons
are
turnedsent
to
the
brain
through
the
auditory
nerve.
Vibra6ons
start
at
the
base
and
travel
along
the
basilar
membrane
toward
tThey
increase
and
decrease
in
their
maximum
displacement
of
the
membradepending
on
the
frequency
content
of
the
signal.
For
a
sine
wave
at
a
par6frequency,
there
will
be
one
maximum.
This
maximum
will
be
near
the
basefrequencies
and
near
the
apex
for
low
frequencies.
Note
the
asymmetry
of
ttraveling
wave
envelope,
which
extends
more
toward
the
high
frequencies.This
will
be
important
for
understanding
audito
This
organiza6on
is
called
“tonotopic”
(from
Gre
What is a critical band?
Auditory nerves respond to select range of frequencies like a band pass filter.one measure of frequency selectivity is the width of the auditory filter, know as the critical band.
Lower frequency masked have more effect,
The
inner
hair
cells
do
the
sensory
transduc6on
from
mechanical
vibimpulses
sent
to
the
brain.
The
outer
hair
cells
refine
the
vibra6on
lthey
act
like
liNle
muscles
that
resonate
at
certain
frequencies.
The
membrane
par6cipates
in
the
transduc6on
and
refinement
processhairs
on
the
hair
cells,
or
the
fluids
around
them,
move.
The
medium
outside
the
cell
is
posi6vely
charged,
the
medium
inside
the
cell
is
nega6vely
charged.
Potassium
ions
are
in
high
concentra6on
outside
the
cell,
but
lowconcentra6on
inside
it.
When
the
hairs
bend,
liNle
gates
on
the
tops
of
them
open
and
let
the
potassium
ions
(K+)
move
through
the
hairs
(because
of
diffusion
and
voltage
forces),
carrying
a
posi6ve
electric
current
with
them.
This
current
depolarizes
the
cell,
causing
the
release
of
neurotransmiNers
into
the
synapses
at
thboNom
of
the
cell,
and
thus
s6mula6ng
the
auditory
nerve
fibres.
Because
of
the
fact
that
movement
in
one
direc6on
opens
the
channels
and
movement
in
the
other
direc6on
closes
them,
the
nerve
fibres
tend
to
discharge
on
the
high
points
of
the
waveform.
So
sta6s6cally,
across
a
set
of
them,
the
temporal
fine
structure
of
the
waveform
is
preserved
in
the
nerve
firing
paNern.
This
providesa
mechanism
for
temporal
coding
in
the
auditory
nerve.
Here
are
the
main
brain
centers
doing
auditory
processing.
Once
the
neural
informa6on
leaves
the
cochlea,
it
goes
through
different
processing
sta6ons
in
the
brain
centers
dedicated
to
processing
auditory
informa6on,
,
all
the
way
up
to
auditory
cortex.
Some
of
it
goes
up
the
same
side
of
the
brain
as
the
ear
it
enters,
bumost
of
it
crosses
over
to
the
other
side.
There
are
centers
such
as
the
Superior
olivewhere
informa6on
from
both
sides
gets
compared.
There
are
also
pathways
sending
info
back
all
the
way
to
the
cochlea,
where
the
infocan
be
modified
before
it
goes
back
to
the
brain.
This
plays
a
role
at
higher
processing
levels,
like
aNen6on,
implying
that
it
is
possible
that
some
of
the
informa6on
is
not
even
gepng
to
the
brain
(the
ear
is
filtering
out
info).
Tonotopic
organiza6on
of
cochlea
is
preserved
(with
different
degrees
of
accuracy)
athe
way
up
to
the
auditory
cortex.
So,
in
each
of
these
nuclei,
the
cells
that
respond
to
higher
frequencies
are
grouped
together,
the
ones
that
respond
to
low
frequencies
are
also
together,
and
in
between
the
high-‐
and
low-‐
frequency
cell
groups
are
the
cells
that
respond
to
middle
frequencies.
As
we
get
higher
in
the
auditory
system,
the
fibers
respond
to
a
wider
range
of
frequencies
(their
frequencyresolu6on
decreases)
and
to
more
complex
tones
(tones
with
a
richer
spectrum).
Further,
in
the
inferior
colliculus
and
medial
geniculate
there
are
inhibitory
(in
addi6on
to
excitatory)
regions.
For
example,
evidence
has
shown
that
in
the
medial
geniculate
some
cells
respond
to
all
the
harmonics
of
a
given
sound
(which
in
turn
implies
that
the
auditory
system
is
biased
to
harmonic
sounds!).
Cells
in
higher
processing
areas
respond
mostly
to
sounds
that
change
over
6me,
whereas
they
“fall
asleep”
with
sounds
that
remain
constant.
Resonance of the ear canal and concha
The upper panel shows the amplification of sound from the entry of the ear to the
ear drum that results from the resonance of the concha and auditory canal. Note thatas much as about 17 dB of amplification is achieved in the mid-high frequency region (2000-5000 Hz , roughly the upper range of the piano). The lower panel shows how
this upper curve (T) can be decomposed into the relative contributions of the concha (1) and the auditory canal (2). Why is the peak of (1) higher in frequency than that of
(2)? How much each of ear part contributes to capture and transmit sound depends
on the size of part of the ear relative to the wavelength of sound, so that the larger
the ear structure, the lower the sound frequency affected by the structure.
Transmission of vibrations through the inner ear
When sound moves the eardrum, the air within the closed middle ear condenses andrarifies, creating sound pressure. This sound pressure moves the little bones in the
middle ear and stimulates the oval and round windows. The stapes acts like a piston, moving the fluid inside the inner ear.
Sound waves apply certain force to each square cm of the eardrum, and all that
energy is transferred to and concentrated in the footplate of the stapes, which is
much smaller than the eardrum. As a result of the size difference, the pressure is
much greater at the stapes than it is at the eardrum (amplifying the sound).
The area difference between the ear drum and the footplate of the stirrup causes a
pressure amplification by a factor of about 15.
Combined, this pressure amplification and force amplification from the ossicles give
about 18 dB of amplification.
Describe the basilar membrane
the basilar membrane unrolled. is narrow, thick and rigid at thebase and thus resonates to higher frequencies. The membrane is wide, thin and
flaccid at the apex and thus resonates to lower frequencies. It varies continuously
between the two along its whole length.
Varies in width thickness and stiffness.
Resonates to dif. Freq. high base to low at apex.
Dependency of basilar membrane peak on freq
This diagram shows an instantaneous snap-shot of the basilar membrane in responseto sine waves of three different frequencies. The dark undulating line is the BM at a
given moment and the dashed line represents the envelope of activity of the BM in
response to that stimulus. The BM won’t go outside this envelope. Notice that the
peak of the envelope is in different places for the different frequencies: closer to the
apex for lower frequencies and closer to the base for higher frequencies.
Frequency selectivity
The ability to process frequency information in small bands (critical bands)
demonstrates that lower-frequency maskers have more of a masking effect
than do higher-frequency maskers.
