- Hi guys, Cliff Olson, Doctor of Audiology
and Founder of Applied Hearing Solutions
in Phoenix, Arizona.
And in this video,
I'm talking about upward spread of masking
and how it can totally destroy the clarity
that you get from your hearing aids.
Coming up.
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Do you ever wonder why you seem to struggle
with your hearing aids?
Well, I don't because I constantly see a variety
of different programming errors
that can lead to a significant reduction in performance
with your devices.
In fact, it does not even matter how awesome
or expensive your hearing aids are.
If they have not been programmed correctly,
you are not going to be getting the maximum amount
of benefit from them.
The bad news is unless you have a decent understanding
of acoustics, you wouldn't even know if one of these simple,
common programming mistakes was being made.
One of these programming mistakes
that I'm referring to can cause a phenomenon
called upward spread of masking
which can totally destroy the clarity
that you get from your hearing aids.
This is why I'm gonna teach you all about upward spread
of masking and what you can do to prevent it.
But before I do,
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Now let's first take a look at how the human ear works
so you can understand the concept
of upward spread of masking.
The human ear consists of three parts:
the outer ear which includes the pinna,
ear canal, and eardrum,
the middle ear,
which includes the three middle ear bones called ossicles,
the middle ear cavity, and the eustachian tube,
and the inner ear which consists of the semicircular canals
which control balance and the cochlea
which is your hearing organ.
As sound enters the ear,
it vibrates the eardrum
which sends that vibration
through these three middle ear bones
and ultimately, into the cochlea through the oval window.
As the stapes bone sends this vibration of sound
through the oval window into the cochlea,
it creates a traveling wave
that vibrates the basilar membrane.
The basilar membrane is coded
with the high frequency regions near the entrance
or base of the cochlea
where the low frequency regions are more
towards the end of the cochlea at the apex.
High frequency sounds only vibrate the base
of the basilar membrane
where low frequency sounds must first travel
through the high frequency ranges
before they reach the lower frequency regions.
If the vibrations of low frequency sounds are too intense,
they can mask over the high frequency regions.
Clinically, this phenomenon is what we like
to call upward spread of masking.
When we look at different speech sounds,
it is important to understand
that the high frequency consonant sounds give the perception
of clarity and the low frequency vowel sounds
give you the perception of volume.
Most individuals with hearing loss
have a sensory neural hearing loss
and most of those individuals have more
of a high frequency loss than they do a low frequency loss.
This typically creates the perception
of you being able to hear someone,
you just can't understand what they're actually saying.
This is why it is so critical to have hearing aids
that are properly amplifying these high frequency sounds
so you can get clarity back.
However, if low frequency sounds are being over amplified
by hearing aids, they can actually mask over your perception
of these high frequency consonant sounds
which take away your clarity and speech.
Of course,
some individuals require low frequency amplification
if they have a hearing loss in these low frequency ranges.
So how do you actually prevent the upward spread
of masking from occurring?
First is by performing real ear measurement.
Real ear measurement is the gold standard way to verify
that your hearing aids have been programmed correctly
to your hearing loss prescription.
If your hearing aids are programmed correctly,
then you can ensure that the low, mid,
and high frequency amplification levels are not going
to be causing upward spread of masking.
If the amplification levels
of low frequency sounds that are measured inside
of your ear canal are exceeding
your low frequency prescriptive targets,
then chances are you're going
to be causing this phenomenon to occur.
Here is an example of what to look
for when having real ear measurement done.
When performing real ear measurement,
the purpose is to verify how much amplification
you are receiving from a hearing aid inside
of your ear canal at your eardrum.
The hash mark line is the prescription
for your hearing loss
and the solid line is the amplification
from your hearing aid.
Ideally, you would want the solid line to overlap
with the hash mark line as closely as possible.
On the right-hand side,
you have the high frequency measures.
And on the left-hand side,
you have the low frequency measures.
As you can see here, there is a pretty good match
of the purple hash mark prescription line
with the solid amplification line,
but take a look at some bad programming,
in this case, with the pink hash mark target
and the solid pink lines.
We are over amplifying the low frequency sounds
and under-amplifying the high frequency sounds.
This is a perfect recipe for upward spread
of masking because this over amplification
of low frequencies are going to drown out the perception
for the high frequencies and they would likely do so even
if the high frequencies were directly on target.
If you want to learn more about real ear measurement
and how it can help you avoid a variety
of different common programming mistakes,
then I will link my video to that in the description.
The second way to prevent upwards spread of masking is
by opening up the venting on your hearing aid ear mold
or your rubber dome.
The perception of low frequency amplification
can only be achieved if you trap these low frequencies
inside of your ear canals.
So if you open up the venting on your ear mold
or open up the venting on your dome,
then it will allow a lot of these low frequencies sounds
to leak out of your ears so you do not perceive them.
Another negative thing that can happen
if you have vents that are too small
or closed off entirely is insertion loss.
This is when you actually give yourself a hearing loss,
in this case, in the high frequency range,
and then if you over amplify the low frequencies,
it's kind of like a double whammy
where you're not getting enough high frequency
and you're getting too much low frequency
which is a really bad case of upward spread of masking.
The important thing to know about different types
of domes and different sizes of ear mold venting is
that you have to strike a very careful balance
between open and closed.
Otherwise, you are going
to significantly reduce the performance of your devices.
A little side note here,
but upward spread of masking is one of the main reasons
why individuals with a reverse slope hearing loss
or a cookie-bite hearing loss do not get a lot
of benefit with hearing aids if you close
off their ear canals
to amplify these low and mid frequencies.
Now I wanna be careful here
because it's important for you to understand
that if you do happen
to have some low frequency hearing loss,
I'm not saying that you should not amplify it.
You should amplify it.
You just have to make sure that you don't over amplify it.
This is another reason
why performing real ear measurement is so critical
when programming a set of hearing aids.
Because if you don't verify,
then you really have no idea what's going on
inside of the ear canal and you could be inadvertently
over amplifying certain frequencies
and under amplifying others.
At the end of the day,
there is a solid chance that if you feel
like you're not getting the right amount of clarity
out of your hearing aids, that a programming error
of over amplifying the low frequencies could be causing
upward spread of masking giving you that perception.
This is why it's so important
for you to have a foundational understanding of acoustics
and the anatomy and physiology of the human ear
so this mistake doesn't happen to you.
That's it for this video.
If you have any questions,
leave them in the comment section below.
If you like the video, please share it.
If you wanna see other videos just like this one,
go ahead and hit that subscribe button.
Also feel free to check out my website drcliffaud.com.
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