Conduction and Middle Ear Flashcards
Define Conduction:
How sound travels through the OE ME and IE
How do sounds travel through the ear?
Through pathways where there is modification in amplitude, frequency and timing
What is the Normal pathway of Air conduction? (OE and ME)
Ear canal-Eardrum-ME bone chain
What is Normal pathway of sound conduction?
Air Conduction
(Ear canal-Eardrum-ME bone chain)
What are the steps of sound conduction in the IE? (3)
- Traveling wave—OC vibration
- Hair bundle deflection
- OHC active force–loop back to IHCs Mech-Electrical-Mech-Hydraulic
In the OE, resonance is due to?
To the standing wave just like a tube sealed at one end
f =n* c /( 4 * L)
What is the length of the ear canal and the speed of sound?
2.6 cm
33100 cm/s
When does resonance (standing wave enhancement) occur?
A tone of fixed frequency is given. Resonance is demonstrated by changing the length of tube. When the relationship between the length and the frequency meet the requirement of resonance, we see the output amplitude (the recorded waveform) increases.
This is easier than showing the resonance of a tube (with fixed length) by changing the frequency of the sound. By changing the frequency of the signal, we need to make calibration to make sure the acoustic output of the speaker remains the same across the frequency range.
What is the definition of Frequency response/Transfer function?
How gain/phase changes with frequency or how does a system responds to certain frequencies
What is gain?
Output/Input, in ratio or in dB
dB gain = ____log (_____________ Ratio) = ____ log (_______________ ratio)
20 log (pressure ratio) = 10 log (intensity ratio)
What can we say about the relationship between the gain and the frequency range of hearing?
The gain varies across frequency range of hearing
Explain what is occurring in this picture.
We can see the ratio gain between the different parts of the OE.
Ratio Gain: G=Output/Input
So for example Flange effect is seen as the difference between Microphone 2 and M1, Concha: M3-M2, etc.
Which parts provide the biggest dB gain between the Flange, Concha and Meatus?
Meatus 10dB
What is the maximum dB gain in the OE?
15 dB
The maximum dB gain in the OE is peaked at how much Hz for adults?
3200 Hz
What is the role of the ME in land animals?
Impedance Matching
Three middle ear mechanisms provide gain for compensating impedance mismatch, what are they?
(1) Area action
(2) Lever action
(3) Buckling action
What is the dB contribution of the Area action in the ME?
25 dB
What is the dB contribution of the Lever Action in the ME?
2.5 dB
What is the dB contribution of the Buckling Action in the ME?
6 dB
The Bandpass in the ME is peaked at __________ Hz.
1000
What is special about the 1000 Hz peak of the Bandpass in the middle ear?
At this Frequency, theoretical calculations of ME gain best predict the actual gain of ME
The decline of the transfer function of the ME at High frequencies is due to:
Due to mass effect: Increasing mass, reduces high-F cutoff
The decline of the transfer function of the ME at Low frequencies is due to what feature and from what systems (3)
Due to elastic feature (stiffness) from TM stiffness, ME ligament tensing and Air Pressure in ME
Which transfer function is narrower and wider between the OE and ME?
OE is narrower peaked at 3200Hz
ME is wider peaked at 1000Hz
If there is a BIG eardrum perforation, how does this AC abnormality impacts hearing? (2)
- Air Conduction goes from the OE to ME air cavity (not through bone chain) and then IE (through both oval window and round window)
- Hearing loss up to 30 dB because of impedance mismatch
If air pathway is BLOCKED, how does this AC abnormality impacts hearing? (2)
Air conduction is not working at all and there is a bigger attenuation expected (e.g., aural atreasia): 50-60 dB (for natural BC)
What is BC?
Bone Conduction. The conduction of sound to the inner ear through the bone of the skull.
What is Natural BC? (2)
Air to skull (air to solid)
Greater loss (50-60 dB) due to mistmatch between air and bone which is bigger than Air-Water impedance
What is Artificial BC and why do we use it? (3)
Natural bone conduction is useless because of the mismatch so we use artificial means to conduct sounds through bone to the IE:
- Bone vibrator
- Skull
- IE
Why do we study Bone conduction? (3)
For diagnosis
For amplification in rehab
For Research
Bone conduction helps us in diagnosis between what?
To differentiate between conductive HL and sensorineural HL
Bone conduction helps us for amplification in rehab using:
BC hearing aids
They are used for various reasons, especially when AC aids do not work appropriately
What are 3 Bone conducting products used today?
- Ear-free headphone
- Hearing aids and assistive listening devices
- Specialized communication products (i.e. for use in underwater and noisy environments)
Which BC device is this?
Bone vibrator or bonephone
Which BC device is this?
Bone Anchored Hearing Aid (BAHA) (Invasive)
What are the advantages of BC compared to AC? (2)
Ear free
High sound clarity in noisy environments
What are the disadvantages of BC compared to AC? (2)
Sound level limit: less gain as compared with AC aids
Narrower/ Reduced frequency bandwidth (bias to low frequency)
True or False: There is MUCH evidence for speech perception difference between ACD and BCD, in both quiet and noise.
FALSE: Limited evidence for speech perception difference between ACD and BCD, in both quiet and noise.
What are differences between AC and BC? (3)
- Different pathways
- Efficacy
In general, AC is better for both normal and artificial ones, however, when AC pathway has problem, BC is better - Resonance or transfer function: different from AC pathway and Varies with conductive pathologies
What are the application problems of BC? (3)
- The feature of vibrator,
- Binaural interaction (BC goes to both ears),
- Masking issue (masking should not go BC)
What are similarities between air-conduction (AC) and bone-conduction (BC)? (2)
Target of BC is the same as AC: cochlear hair cells.
Cochlear mechanics is almost the same.
What is the evidence that the target of BC (cochlear hair cells) is the same as AC?
AC vs BC cancellation, apply a tone of the same frequency through AC and BC but opposite phase.
Describe the Model Pathways for BC and AC in hearing
Why does conductive pathologies impact BC so much?
Because BC highly overlaps with AC as seen on the Model Pathways so it is affected by conductive pathologies as well
Describe the BC mechanisms (Pathways) (2):
BC by AC(via ME)
BC (bypass AC)
What occurs in the BC pathway from BC by AC (via ME)? (2)
- Osseotympanic BC
- ME Inertial BC
What occurs in the BC pathway bypassing AC? (3)
- Compression/Distortion BC.
- Fluid Inertia in Cochlea
- CSF (inertia, compression)
Describe Osseotympanic Bone Conduction: (3)
- Vibration of Skull including the walls of ear canal and ME
- Radiation into ear canal and ME
- Then sound conducts through AC from ear canal (Vibration also leak out related to occlusion effect)
In Osseotympanic Bone Conduction the frequency most important is at:
Low-f (Evidence: AC/BC cancellation in external ear canal for fre. < .7 kHz)
In otosclerosis, what is the amount of dB loss at low-f?
Up to 60 dB Low-f AC hearing loss in Otosclerosis.
In those cases, this BC is eliminated. BC thresholds can remain normal.
What is the relationship between the occlusion effect and Osseotympanic Bone Conduction ?
when EC is blocked, this component OBC becomes more important
