Otoacoustic Emissions Flashcards
Who is George von Bekesy?
Joined Harvard in 1947, under Stevens
Partially dissected BM (in cadavers)
microscope with a strobe light to measure movements of BM (to 1/1000th of an mm) he had to slow down the BM
Stroboscopy is a visual ‘beat’ effect
What did George find?
1961 Nobel
The tuning wasn’t sharp enough to account for human frequency discrimination
it was a smooth-traveling wave
Explain the Wave problem. (2)
- Hearing is sharply tuned, but the traveling wave wasn’t (not sharp enough) to explain how our hearing is sharply tuned
- Békésy spent his career working on a model of neural lateral inhibition to explain human abilities
- This turned out to be wrong but inspired similar work in the visual system
What is the crazy theory of Thomas Gold (1948)?
- Engineer argued that the passive cochlea model was not tenable (can’t work)
- There had to be an active mechanism to add energy to the vibration
What did David Kemp discover?
Discovery of OAE
Shows the response from Clicks in the ear, even after the click, there is still vibrations showing the active mechanism contribution in the IE
What does this graph show?
Responses to Clicks, Tone Bursts
What are the reasons that the stapedius reflex is not the reason for OAE? (4)
- Low stimulus levels - presentation level too low for stapedius
- Ipsilateral only
this “echo” only detected ipsilaterally - Sensitive to polarity
reflexes are independent of stimulus polarity, but this “echo” inverts with inverted polarity - Not sensitive to rate
the response can be elicited at rates from 1-80 Hz (unlike neuro-muscular responses
Thus, sound energy appears to be _____________________________________, into the external ear canal, for some_____________________________after impulsive acoustic excitation.
Thus, sound energy appears to be emitted by the auditory system, into the external ear canal, for some tens of ms after impulsive acoustic excitation.
What are the roles of OHC?
Provides active amplification by physically enhancing movement of the basilar membrane
OHCs are motile, they move in response to sound, adding energy to the mechanical movement of the BM
What is Furosemide?
Medicine that damages OHCs (interferes with OHC motility)
What is the meaning of the term “cochlear amplifier”?
Enhances vibration of basilar membrane near displacement peak, for softer inputs (< 60 dB)
How is the cochlear amplifier accomplished? (2)
accomplishes this in TWO ways:
1. OHC somatic motility
the cell bodies elongate (like the dancing can)
this plays an important role in the generation of some OAEs, and in the ability to get any OAEs at soft levels
- Stereociliary transduction
the stereocilia also elongate in response to sound and amplify the movement—and this plays an important role in generating some OAEs
What are the types of Otoacoustic Emissions? (5)
What are SOAEs?
present in most ears
tend to be larger in females than in males
they also vary along a gender continuum
Frequencies are stable in a given individual and amplitudes may fluctuate, related to hormone levels
Most often occur between 1 and 2 kHz
decrease with aging (hearing loss)
Can SOAE be heard and cause tinnitus?
Can be heard but need a microphone that picks up sounds lower than -10 dB HL, don’t cause tinnitus
How do TEOAEs work? (2)
- The probe has a tiny speaker and a tiny microphone
- A short signal is played to the ear
generally 80 µs click
the microphone records the sound that comes from the cochlea, after the click is over
What are some caveats about TEOAE? (2)
- The sound produced by the cochlea is very soft
- Can’t record unless: a very sensitive microphone AND many responses are averaged
How long do Transient Click-Evoked OAEs tests take?
Very fast, about a minute
How does the frequency gets affected by a tone or clicks?
Frequency same as when using tone, but frequency change over time when using clicks, the frequency of the output decreases over time
Each cochlear ‘echo’ must happen after sound has travelled to a place in the cochlea
The echo then needs to travel back out (and through the middle ear) to be picked up by the microphone
What responses on the BM do clicks provide?
Clicks can provide a place-specific response
What is another aspect that Clicks can provide in TEOAEs? (2)
- the health of different places on the cochlea (i.e., the OHCs) can be inferred by the amplitude of the response
- on the lower right is the frequency transform of a click-evoked OAE
green is response, red is noise
What is TEOAE really useful for?
- Great for infant hearing screening which appears large in babies
- Similar to SOAEs
larger in females
largest between 1 and 2 kHz
How are TEOAEs sensitive to hearing status?
May be present for mild loss, but highly unlikely to be present for moderate or greater loss
What are Stimulus-Frequency OAEs?
Recording the cochlea you’re playing a stimulus at the same frequency
A cool way to discriminate whether its the stimulus or a response, as the tone sweep is played to the ear canal at low levels, the input sound and the emission sound are close in level, and you have spectral periodicity
How are we able to get Spectral Periodicity?
Because sounds are added together so pressure changes!
Correlated sounds vary together… here are two correlated sounds that are in phase:
If we have 2 perfectly correlated sounds, with equal pressures, in phase the resulting sound has _____________________________ and the sound is ___ dB higher.
If we have 2 perfectly correlated sounds, with equal pressures, in phase the resulting sound has twice the pressure
= 20 x log10 (2)
= 6 dB
and the sound is 6 dB higher.
Correlated sounds vary together, what would occur if the two wounds would be out of phase?
Cancellation Effect
If we have 2 perfectly correlated sounds, with equal pressures, but out of phase, the resulting sound has__________________ and there is __________________.
If we have 2 perfectly correlated sounds, with equal pressures, but out of phase, the resulting sound has zero pressure
= 20 x log10 (0)
= 20 x -infinity
and there is no sound.
If we have 2 uncorrelated sounds, the pressure differences between them are ________________________, so no constant phase or pressure relationship. We simply add the intensities.
If we have 2 uncorrelated sounds, the pressure differences between them are constantly different, so no constant phase or pressure relationship. We simply add the intensities.
= 10 x log10 (2)
= 3 dB
and the sound is 3 dB higher.
What is the Phase (time) Relationship?
If the cochlear “echo” emission is delayed by 5 ms…
What is spectral periodicity?
As you run through the frequencies, they will add, then cancel, then add, then cancel, etc.
This is called “spectral periodicity”
What about the levels when we run through the frequencies depending on phase?
If the sounds are different in level and out of phase…
20 dB + 70 dB =
69.9724 dB
If the sounds are different in level and are in phase…
20 dB + 70 dB =
70.0274 dB
Phase only matters when the levels are similar!
How do DPOAEs work?
- Instead of a noise, or a tone sweep, two tones are played
we call these F1 and F2
the cochlea produces a third frequency (a distortion product)
this is the emission
two separate speakers are used for each primary (why?)
What occurs on the BM from DPOEs?
- These tones have overlapping displacement patterns on the BM
- Frequency ratio usually 1.2 or 1.22 (i.e., a constant ratio or distance on the BM)
if F1 is 1000 Hz, F2 is 1200 or 1222 Hz
distortion is created in near the F2 place (where the travelling waves overlap the most)
the frequency of the distortion is primarily 2F1-F2 – called the cubic distortion product
F1 = 1000, F2 = 1200, 2F1-F2 = 800
Why are DPOAEs more useful than Stimulus-Frequency OAEs?
Since the distortion is at a different frequency from the stimulus tones, it is much much much easier to measure
What are the clinical values OAEs? (2)
- Screening for hearing loss
highly unlikely that OAEs will be recorded for moderate or greater loss
transient and distortion-product OAEs are the most useful - Sensitive measure of cochlear health
What are the uses of OAEs in General Clinical Practice?
- Assesses cochlea (outer hair cells), providing diagnostic specificity related to the sensory organ
Assessment of cochlear dysfunction
Méniere’s
Ototoxicity
Noise Damage
Plays a critical role in distinguishing neuropathies from sensory loss
consider implications of normal cochlear function when hearing loss is present
Testing is rapid and objective
How does the tympanogram work
Sweep of pressure
Gain must increase to keep a constant level at the microphone when less is reflected back (i.e., when admittance is high)
What does this place signify on the tympanogram?
Admittance when lots of positive pressure in the ear (ear drum stiff)
= external ear canal admittance in mmhos (or volume, in cc)
What does this place signify on the tympanogram?
Peak admittance. The TM and ossicles are maximally set in motion.
It occurs here with atmospheric pressure.
What does this place signify on the tympanogram?
The peak admittance minus the ear canal admittance (or volume). This
is the admittance (often called compliance) of the middle ear.
What does the peak represent in the tympanogram?
The peak pressure is the pressure at which the system is maximally compliant.
What are the two types of tympanogram?
What is the laterality of the Acoustic Reflex?
Bilateral
The rule in AR measuring: for contralateral recordings, we label the response by ______________________________________
The rule in AR measuring: for contralateral recordings, we label the response by the ear of presentation
How does the probe test for the AR?
ear canal pressure adjusted to peak pressure (for best sound transmission)
What is the pathway of the AR?
CN - 8th nerve - VCN- SOC - (FFN - 7th nerve stapedius Ipsi and contra)
Acoustic Reflex Site of Lesion —
