Lecture 4 Flashcards
What are the 4 behavioural audiometry/psychoacoustic tests?
- Pure tone audiometry
- Clinical decisions
- Speech audiometry
- Masking
What is identification?
Identifying that there is a problem
- a hearing loss
- a vestibular problem
- problems hearing at school
Identification is too light of a description to count as a ____
Diagnosis
What is diagnosis?
- Determining the nature of the condition (based on assessment)
- This may or may not include etiology (the underlying cause of the condition)
What are some things audiologists diagnose?
- A moderate sloping to severe
- Sensorineural hearing loss bilaterally
- BPPV
- Auditory processing disorder
- Auditory neuropathy spectrum disorder
- noise-induced mild 4 kHz notch
pulsatile tinnitus
You often don’t know the ____ behind a diagnosis
Etiology
Can audiologists diagnose?
Yes, it is within our scope of practice
Where CAN’T audiologists diagnose?
Ontario
Ontario’s language confuses ____ with ____
Diagnosis, etiology
Audiologists in ontario can’t diagnose, instead they can ____ and ____
Assess, describe
What two things can audiologists identify in Ontario?
ANSD and APD (considered to be symptoms and not disorders)
What wording should be used in ontario?
In Ontario, use wording like ‘this is consistent with’ or ‘this may suggest’
As audiologists, what is our ultimate focus?
Hearing function and communication
Tight link between ____ and ____ means that a good audiologist should understand both
Physiology, perception
What things must be diagnoses by an otlogist?
- Schwannoma
- Infections
- Meniere’s
- Otosclerosis
- PET
- Superior canal dehiscence
What are the 3 ways to talk about an audiogram?
- Y axis
- X axis
- Z axis
Explain the key points of the Y axis
The level
- dB HL (air and bone)
- Loudness Contours and Growth
- Intensity Discrimination
Explain the key points of the X axis
Frequency
- Place Specificity
- The Basalward Shift
Explain the key point of the X axis
Temporal Integration
What is the purpose of the audiogram?
- Provides information about likely communication problems
- Critical for audiologic treatment
What are 4 limits of the audiogram?
- Poor for distinguishing sensory versus neural loss
- May miss significant loss of hair cells
- Does not assess temporal processing
- It is the beginning of assessment, not the end
What is behavioural audiometry looking to find?
- Functional characterization of clinically relevant psychoacoustic details
- How is this person different from what we expect
- Goal is not description of ability, but description of different ability
What is MAF?
Minimal audible field (open ears)
What is MAP?
Minimal audible pressure (headphones)
Do outer ear effects play an important role in diagnostics?
No, usually we have the ear plugged when testing and treating
However, in everyday life we hear better with MAF because of the gain from the outer ear
The middle ear is not good at transferring ____ frequencies
Low
The ____ coupled with the ____ is responsible for MAF
Middle ear, outer ear
The shape of hearing reflects ____ and ____
Middle ear, outer ear
Is the natural shape of the absolute threshold curve relevant for diagnosis? What needs to be done?
No
dB HL is a flattened version of the MAP
How do we find the HL from SPL?
dB SPL - RETSPL = dB HL
What is RETSPL?
Reference equivalent threshold sound pressure level
What does RETSPL represent
Middle ear transfer function
What are RETSPLs?
- Levels in dB SPL that correspond to 0 dB HL, as measured at a calibration point
- Inserts: 2cc coupler
- TDH: 6cc coupler
- Speakers: microphone in centre of head
What is 0 on an audiogram?
The average lowest threshold
Explain the importance of understanding why not every ear is the same?
The actual sound level at the eardrum at a given dB HL is…
1. Not the same across individuals
2. Not the same across different earphones for a given individual
Can dB HL change due to different ear canal size?
- Smaller ears, more pressure, hear at a softer level
- Larger ears, less pressure, hear at a higher level
- Hearing ability doesn’t change, ear canal size changes how you hear
What will a leak with insert and TDH headphones show? What also shows this?
Low frequency drops, perforations
What is the best to use to get the best predictor of real-world hearing? But why is it bad?
Sound field, but its not good because you cant control which ear the sound is going to
____ may be less similar to sound field (less predictive of real-world hearing)
Inserts
____ are just as correct for occluded-ear hearing (trough a hearing aid or airpods)
Inserts
Will bone conduction be affected by perforation?
No
What are the 5 mechanisms of bone conduction? Which are the most important? Which is the largest effect?
- Sound radiated into the external ear canal
- Middle ear ossicle inertia
- Inertia of the cochlear fluids
- Compression of the cochlear walls
- Pressure transmission from the cerebrospinal fluid
Top 3 most important (3 is largest effect)
Mechanisms of BC (1)
Sound radiated into the external ear canal
- open eear
- closed ear
- Open ear: minimal contribution
- Plugged ear: most important contribution from ~400-1200 Hz (radiates from cartilage and TM); occlusion effect
Mechanisms of BC (2)
Middle ear ossicle inertia
- how much contribution
- what does it explain
- Contributes a small amount between 1000 and 3000 Hz
- Helps explain Carhartt’s notch
Mechanisms of BC (3)
Inertia of the cochlear fluids
- The most important source, especially when ear is open
- Fluid is fixed in the cochlea, so moving back and forth, the fluid pushes against the hair cells
Mechanisms of BC (4)
Inertia of the cochlear fluids
- how much contribution
Possibly small contribution above 4 kHz
Mechanisms of BC (5)
Pressure transmission from the cerebrospinal fluid
- how much contribution
Possibly a small contribution
Explain the inertia of cochlear fluids (what is the fluid doing)?
- While the bone vibrates, the perilymph tries to stay put.
- The oval window has very high impedance, so the fluid is forced to move with the bone to some degree
- The inertia of the fluid is the main contributor to BC hearing
- Your client is concerned about his hearing. He reports that he hears too many sounds. He can hear his footsteps.
- Using insert phones, you measure normal thresholds (worst threshold is 15 dB HL at 250 Hz, with an air-bone gap)
- Why the ABG?
- Leak from inserts
- Hyperacusis
- Superior canal dehesince
AC results in pressure to the OW that is dissipated towards the third window, so air thresholds are poorer (ABG)
What do audiometric responses depend on?
Pathways of sound
Bone conduction thresholds depend on ____ major pathways
3
Air conduction thresholds depend on ____
Air conduction thresholds depend on transducer/coupling to ear
What are our best AC thresholds determined by?
Our best air thresholds are determined primarily by the shape of the middle ear transfer function—and outer ear resonances if done in sound field
Why do air and bone thresholds ‘match’ in dB HL (e.g., average normal threshold is 0 dB HL)?
We calibrate our equipment so that:
- Air and bone conduction thresholds match
- Average threshold is a flat 0 dB HL for every transducer
- Assuming an average ear!
Why are audiograms shown as a flat line?
Audiograms show normal as a flat line; makes deviations (hearing loss, ABGs) easier to see
Can you see some abnormal variations in AC and BC that have nothing to do with hearing loss?
Differences in ear canal acoustics (e.g., size), middle ear transfer functions, ossicular inertia etc. will all lead to some variation in AC and BC thresholds across people (that have nothing to do with hearing loss!)
Can BC thresholds be worse than AC thresholds?
Only if there is a calibration issue or if the person isn’t close to “average” (because they are calibrated to be equal on an average)
Where are equal loudness contours referenced?
Referenced to loudness at 1kHz
Where does loudness grow most quickly?
Low frequencies
Are 70dBHL sounds at 200 and 1000Hz equally loud?
- Loudness at 200 and 1000 are about the same
- 100 and 1000 are different
Loudness scaling - SS Stevens’
- Referenced to loudness at 1 kHz, 40 phons
- Loudness doubles with a 10 dB increase (Stevens)
Loudness scaling - RM Warren
- Loudness scaling experiments are imperfect, since subjects ‘calibrate’ scales to range of stimuli presented
- Warren made only one measurement per subject, and found that doubling corresponds to 6 dB instead of 10 dB
What is recruitment?
With cochlear hearing loss, loudness tends to grow more quickly
What is someone has normal hearing in one ear and a cochlear loss in the other?
When one ear is normal, recruitment can be detected with the ABLB: the alternate binaural loudness balance test
What was Jerger’s idea on recruitment?
If loudness grows more quickly in impaired ears, then perhaps they can detect small changes in level better (test idea from Jim Jerger)
What test did Jerger make to determine recruitment and how did it work?
- The SISI (short-increment sensitivity index) for diagnosing recruitment
- Jerger suggested that recruitment might give rise to better level discrimination
Explain how the SISI works
- A tone is a level that is changing by 5dB (they tell you when it changes in level)
- After presenting five 5dB changes, it presents 1 dB changes in level
- Count # 1 dB changes identified (out of 20), at 20 dB SL
- If you can hear them, recruitment is diagnosed
Explain Weber’s law
- The smallest detectable change is a constant proportion of stimulus magnitude
- In wide-band noise, we can detect an intensity change of about 10-30% (0.5-1 dB)
What is the near miss of Weber’s law?
- Weber’s law does not hold for pure tones… level discrimination improves at high levels
- 1.5 dB at 20 dB SL
- 0.3 dB at 80 dB SL
- “Near miss to Weber’s law” (loudness discrimination gets better at high levels)
At high levels can hear very small levels in change
Is the SISI a good test of recruitment?
- The SISI test always diagnoses recruitment because loudness discrimination is naturally better at high levels (the “near miss to Weber’s law”)
- It has no clinical value for diagnosing recruitment
What causes recruitment in normal ears?
Faster growth of loudness at LF because of the middle ear
Is recruitment pathological?
No
What causes recruitment in hearing loss?
- Inability to hear soft sounds is a function of loss of mechanical amplification (OHCs) for soft sounds
- Loud sounds may create similar velocity on BM, since OHCs were not involved
- Recruitment can be fully explained by BM mechanics – no neural pathology required
Do audiologists diagnose recruitment?
No
Even though the SISI isn’t good for diagnosing recruitment, what can it diagnose?
The high level SISI (at 80dB) can help diagnose neural problems (if they cant detect the 1dB difference it can mean a neural loss in that ear)
The x-axis on the audiogram is for ___ and ____
Pure tone frequency & place specificity
What is place specificity?
Presenting a tone at a certain frequency goes to specific spot on the BM (it will stimulate a specific spot at a very soft level)
What happens to place specificity as you go up in sound level?
More of the BM will be stimulated
Auditory nerve response picture
- what do you see at 20dB
- what do you see at 70dB
- At 20dB, you can see where it is stimulating the BM
- At 70dB, a lot of the BM is being stimulated
Many ____ neurons respond at high levels
Off-frequency
Place selectivity is ____ at high levels
Poor
Place selectivity is looking at the response of what?
Response of a single auditory neuron to tones of different frequency
What kind of tone (low frequency or high frequency) is likely to elicit responses across the widest number of neurons?
High frequency
What kind of tone is being played to show the CF?
Low frequency
How is functional sensitivity determined?
By the shape of neural tuning curves
What is the shape of the tuning curve created by?
Shaped by the travelling wave which depends on the structure of the basilar membrane
Why does a neuron not respond to any sound higher than the CF?
Because of the shape of the travelling wave
What gives the sharp dip in the tuning curve?
The hair cell active component
The primary determinants of hearing sensitivity are ____
Peripheral (structure of middle ear, basilar membrane etc.)
At high levels, the x-axis poorly represents ____
- Place
- The OHC aren’t doing much at high levels (we are looking at broad traveling waves)
Explain isointensity curves
- As we change the level of the stimulus, there is a shift in frequency on the BM
- Isointensity curve response along the BM for different levels (measuring the BM at a particular place)
- As we raise stimulus level, it stimulates a lower CF better
What happens to the peak of the travelling wave as you go from soft to loud sound level?
- At a soft level, traveling waves peaks and as level is increases, the peak of the traveling wave peaks more towards the base
- A neuron may respond best to 2k at high levels and 1k at low levels
Maximum velocity is more basal at ____ levels
High
Bob and Larry picture
Bob is responding to 2K at high levels and 1K at low levels
What makes an audiogram look the way it does?
The traveling wave mechanics and the basal shift
What explains why we get 4k noise notches?
The basalward shift (people often get 4k because the peak frequency is around 2700Hz, therefore that’s where most sound is, however due to the basal shift, most hair cells are damaged at 4k)
____ losses are always steeper than ____ losses
HF, LF
The z-axis is showing us ____
Time (temporal integration)
What are 3 important points about the tone being presented?
- Threshold becomes lower as the length of the tone is increased
- Thresholds are stable as long as tones are > ¼ second
- We can ignore time if tones are sufficiently long
Make sure tones are loud enough to allow for ____
Temporal integration
Why is the RETSPL so large at low frequencies?
ME transfer function
Why does a third window create an ABG and lead to dizziness with loud sounds?
Inertia of cochlear fluids
Why does a large low-frequency dip in insert thresholds suggest a perforation?
Leak of sound
Why don’t we see reverse ski-slope audiograms?
Basalward shift
Why don’t we see right-corner audiograms?
Basalward shift
Why can BC thresholds be worse than AC thresholds?
Ear canal size
Why does noise-induced hearing loss typically start with loss at 4 kHz?
Basalward shift from the peak of the ear
