Hearing Aids
Will Styler - LIGN 113
Today's Plan
What does a hearing aid do?
Signal Processing in Hearing Aids
Hearing aid types
Hearing aid fitting
When don't hearing aids work?
Addressing lingering questions from the course so far
CAPEs
What does a hearing aid do?
Hearing Aids amplify the input signal!
It can be uniform throughout the frequency domain, or targeted
A microphone picks up on the signal
It's converted to digital form and processed
It's played back into the ear canal in louder (potentially modified) form
Hearing Aids turn incoming acoustic signals into louder acoustic signals
Sometimes with some intermediate processing
... and everything happens before the tympanic membrane
Different hearing aid types have different advantages
Cosmetic advantages
In ear vs. Behind Ear vs. In-Canal
This is also a realm for middle-ear implants!
Degree of amplification
- BTE is usually able to offer greater amplification than CIC, e.g.
Vulnerability to ear canal change
- Kids don't want in-ear aids for changing ears
Do you want any sound to pass through at all?
- If you're just amplifying part of the spectrum, let natural hearing work too!
There's a lot more to this choice
... but your book goes into details!
And you'll figure this out as you go about...
Fitting Hearing Aids
We're not getting too deep into fitting!
Hearing aid fitting is a whole subdiscipline
There are thousands of variants and types
Every company has their own secret sauces and marketing hype
- The products are roughly equivalent in quality within a price range
We're going to talk about the basic concepts
- ... and leave the rest to the future!
How are hearing aids fitted?
Check the hearing
Figure out the pain points for the patient
Select the best choice given the constraints
Instruct the patient on their use
Tune them as needed
The focus needs to be on patient outcomes!
If the hearing aid isn't helping where they need help, it's not doing any good!
Good fitting may require multiple tuning sessions
Adjusting frequency responses
Adjusting filtering settings
Adjusting amplification strength
The best hearing aid in the world doesn't do anything on the nightstand!
People are often reluctant to use Hearing Aids
Partly due to stigma
Partly due to poor prior experiences, or family experiences
Partly due to the complexity involved
Often due to cost
- Which pushes people towards...
Hearing Amplifiers and PSAPs
Not all 'hearing aids' are hearing aids
- There exists a shadowy world of 'hearing amplifiers' or 'personal sound amplification products' (PSAPs)
These are one-size-fits-all
'Turn the screw for more volume in all frequencies'
'Use different tips for different ears'
'We made an Airpod with a microphone which plays things louder'
Meant to be cheap, not comfortable
This line is about to get blurry
Real Hearing Aids can now be sold Over-The-Counter in the US
- No audiologist is needed
Watch for big companies to enter the space with 'smart hearing aids'
Ask how smart they are!
- ... and whether they're adapting to the person's hearing loss at all
Challenges for Over-the-Counter Products
Characterizing the level and nature of the hearing loss
Tuning the devices to patient needs
Overamplification
One-size-fits-all form factors
Ongoing support and maintenance
Loss of screening for other disorders
- Wax buildup? Choleasteatoma? Acoustic Neuroma?
When don't hearing aids work?
Hearing aids offer great outcomes for lots of folks!
Amplification can be a great help for many
Loss of hearing can be very difficult for folks who've always had it!
... but hearing aids aren't always enough!
Even when they work, it's not perfect hearing!
With loss of OHCs, the sound may be perceptible, but it won't be as clean!
- Frequency specificity is lost
"Notched" loss, where some frequencies are missing, won't be fixed here
Dynamic range losses mean that distortion is inevitable
Take care of your ears! Technology cannot save you!
Hearing Aids make use of the existing auditory physiology
- "Let's make sounds loud enough that they'll pick it up!"
Hearing aids don't work with profound conductive loss
Then you'll want to use bone conduction
Bone conduction Hearing aids
Bone anchored implants
Or maybe a middle-ear implant!
- Which interfaces directly with the ossicles
None of these options work when there's no cochlear transduction
If the person can't turn sound into nerve impulses, amplification isn't the problem!
This can also happen if the loss is so profound that sufficient amplification isn't possible
In these cases, patients might consider a surgical option
Lingering Questions? Muddy points?
Wrapping up
Hearing aids amplify signals moving into the middle ear
They have many different kinds of on-board processing
They can also incorporate other sources of sound
Different form factors make for different experiences
Fitting is complicated
Hearing aids don't always work!
Next Time
The surgical option!
