OUTER
HAIR CELL FUNCTION
Implications
for Hearing Aid Fittings
Traditional
View
-
Cochlea was a ____________organ
that converted the ___________ vibrations of sound into neural energy
-
New Discoveries change
this View
-
Kemp (1978) discovers
that the cochlea is able to ____________ sound
-
Brownell & colleagues
(1983, 1984, 1985) discover that outer hair cells possess a unique __________
capacity.
Historical
Overview of
Cochlear Function
-
_____________ (1960)
contributed much knowledge re: the ______________ tuning of the Basilar
Membrane…
-
i.e., most sensitive
to low freq at the ____________ end of the cochlea
-
and most sensitive to
high freq at the ____________ end of the cochlea
Mismatch
between tuning curves
-
Kiang et al (1965) found
that mechanical tuning curves were much _____________ than neural
-
Russel & Sellick
(1978) found the same was true for ____________hair cells
-
Rhode, Ruggero, Robles,
Sellick (1980’s) found improved ways to measure the _______ tuning curves
Another
Major Discovery Supporting Active Process
in the Cochlea
-
Rhode and Sellick et
al (80’s) found that ____________ lead to degradation of the _______________
mechanical tuning of the healthy ear
-
So Bekesy’s curves were
______________ because of _______________ effects in his animals
Conclusion
Re: Cochlear Tuning
-
It was concluded that
the narrow mechanical tuning of the _______________cochlea was based on
physiologically ________________ mechanism.
-
Anoxia resulting from
_______________ results in changes in the “energy consuming or active process”
required for ______________ tuning
-
So….it is _____________energy
from an active process that that contributes to the ____________ mechanical
tuning
OK…Very
Interesting, BUT….
-
How does tuning relate
to hearing aid fittings????
-
Is narrow tuning necessary
for Speech Recognition????
-
Does narrow tuning relate
to loudness growth???
-
Difficult to show direct
evidence because of the ________________ of the speech signal!
So are
we convinced there is some relationship worth our understanding?????
Then Carry
on with the discussion……..
How might
this active process be mediated?
-
Brown et al (1983, 1984)
studied the effects of stimulating the crossed __________ (COCB)
-
The COCB is a collection
of neural fibers starting the __________ that travel to the cochlea and
terminate primarily on the ______________!
-
Stimulation of _______________
results in changes in the hair cell receptor potentials and __________________in
the ear canal.
-
Outer Hair Cell Function
-
An OHC can be removed
and it’s function maintained up to ________________
-
Healthy OHC is like
a _________________
-
resists bending and
deformation by probes
Electrical
stimulation results in shape changes
-
hyperpolarizing causes
________________
-
depolarization causes
_________________
-
The source of movement
is the ________________
-
Each cell has a standing
current that is modulated when ____________ are bent as a result of cochlear
partition displacement
-
This creates _______________
that are transmitted back to the ear canal as Otoacoustic Emissions
-
OHCs are arranged so
that there is ample space around them to allow for _____________
-
OHC apical end is anchored
in the _________________
-
OHC basal end makes
contact with ________________ nerve terminals
-
Aspirin toxicity results
in an increase in __________________
-
This results in the
cell flattening and not holding the normal ________________
-
_____________
results in results in a blocking of OAE’s
.................Therefore,
....................This relationship (aspirin toxicity and loss of OAE’s)
-
is the strongest argument
for the role of ____________and the ____________ of OAE’s
So what
does loss of OHC function have to do with fitting hearing aids????
Read Chap
8….
Explain
relationship with three types of hearing loss and type of hearing aid fitting
Type I____________??
Type II____________??
Type III___________???
Type 1
Hearing Loss
-
Degree of Loss
-
AE present __________
-
Loss of __________ Hair
cells, normal __________ Hair Cells
-
Loudness Growth
-
Loss of sensitivity
for________ Sounds
-
Need amplification of
________ Sounds
Loudness
Growth-Type I Loss
Type II
Hearing Loss
-
Degree of Loss
-
OAE present ____________?
-
Loss of __________ Hair
cells, Loss of __________ Hair Cells
-
Loudness Growth is __________
-
Loss of sensitivity
for __________ Sounds
-
Need amplification of
___________ Sounds
-
Speech Recognition________________
Loudness
Growth-Type II Loss
Type III
Hearing Loss
-
Degree of Loss
-
OAE present?? _____________
-
Loss of __________ Hair
cells, Loss of ____________ Hair Cells
-
Loudness Growth?_____
-
Loss of sensitivity
for ___________ Sounds
-
Need amplification of
___________ Sounds
-
Speech Recognition____________
-
Dynamic Range_____________
Loudness
Growth-Type III Loss
Fig 8-13 (Berlin, 1996)
Consider…..effect
of OHC
-
Ruggero
& Rich (1991) Fig. 8-18 (Berlin, 1996)
-
Compare
HA to OHC amplifier Table 8-2 (Berlin, 1996)
Hearing
Aid Fittings
-
Type I Loss____________________
-
Type II Loss____________________
-
Type III Loss____________________
Restoring
loudness for Type I Loss
Fig 8-17,
8-20, 8-21 (Berlin, 1996)
New Info
on “Dead Regions in the Cochlea”-Brian Moore et al. (2000)
Role of IHC-
-
Transduce ___________
vibrations in the cochlear into neural activity
Role of
OHC-
-
Enhance the sensitivity
to ___________ sounds by
-
Increasing the response
on the BM for freq close to CF
-
Increase sharpness of
___________ on the BM
-
Produce a ___________
(compressive) I/O function for freq close to CD
-
Contribute to production
of ___________ tones
Damage
to IHC-
-
Less efficient ___________
of mechanical vibration into neural activity
-
Loss of sensitivity
-
Reduced information
flow in the ___________ (___________ transmission)
-
In extreme cases..no
transduction of activity at some regions of BM- ___________ regions
Damage
to OHC-
-
Reduced sensitivity
to ___________ sounds
-
Reduced sharpess of
___________ on the BM
-
More ___________ I/O
functions on BM, ie loudness ___________
-
___________ of Combination
tones…
Note that
threshold elevation
-
Can occur as a result
of ___________ or ___________ damage, or a mixture of the two
-
Moore developed test
to detect ___________ regions
Test for
Dead Regions
-
Measure thresholds in
___________
-
Measure thresholds in
___________ noise
-
If thresholds shift
more than ____ dB more than normal shift…there is a dead region.
-
If HL >80 dB, nearly
___________ dead regions
Implications
for fitting HAs?