CSD 5400 REHABILITATION PROCEDURES FOR THE HARD OF HEARING Amplification Hearing Aids.
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Transcript of CSD 5400 REHABILITATION PROCEDURES FOR THE HARD OF HEARING Amplification Hearing Aids.
CSD 5400REHABILITATION
PROCEDURES FOR THE HARD OF HEARING
AmplificationHearing Aids
Preliminary Remarks
One of the most critical elements of any rehabilitation plan (child or adult) is the fitting of appropriate amplificationThis is the only recognizable way, at this
time, to maximize residual hearingThe primary objective of modern amplification
theory is to make speech audible without introducing distortion and to restore a more “normal” range of loudness experience
Preliminary Remarks
Fitting of appropriate amplification should only be done by a trained professionalAudiologistLicensed hearing aid dispenser
Hearing aids are the most common form of amplification, but not the only one
Selecting theHearing Aid Candidate
What factors do we consider, after a hearing assessment, in making decisions about recommending amplification?
1. Degree of Hearing Loss
Right or wrong, this continues to be a major parameter in deciding whether or not to recommend amplificationMany studies demonstrate poor correlation
between hearing sensitivity and self-perceived handicap (activity limitation)
In general, as the degree of HL increases, the need for amplification increases, but overall HA benefit decreases
“Problem Fittings”
Unilateral hearing lossLots of residual hearing
Mild hearing lossNormal hearing throughout a broad area
of the audiometric range
Profound degrees of HL/very little residual hearing
Unusual/atypical configurations
2. Motivation Very common for people to
believe they have HL, but only a small percentage will ever utilize HAs or even try them
Why?Poor advice from MDsLack of understanding of HL
and HAsFinancial concerns
Here are some common factors that cause people to try amplification
3. Acceptance of Hearing Loss
How realistic is the client regarding the amount or type of communication problems the hearing loss is causing?
Is the client still angry about the hearing loss?
4. Cosmetic Concerns
“Hearing aid effect”It is realStigma
How concerned is the client over hearing aid size and style?
Hearing Aids
First hearing aids were manufactured by Siemens Electronics in 1912
The two major trends that drive current hearing aid design include
1. Miniaturization• Overall size, components, batteries
2. Enhanced signal processing
Hearing Aid Development
http://dept.kent.edu/hearingaidmuseum/development.html
Recent Advances in Signal Processing
Multiple memoriesProvides access to different amplification characteristicsIncreases flexibility
Noise reduction circuitsSophisticated ways to improve the signal-to-noise ratioMajor complaint of most listeners
Feedback controlFeedback is the audible signal related to an interaction
between certain components of a hearing aidAs hearing aids became smaller, feedback was a major
limitation and complaint
Recent Advancesin Signal Processing
ProgrammabilityAllows the dispenser to set and control a number of
different properties of the HAIncreases “precision” of the fittingIncreases hearing aid flexibility
Digital processingMajor tech advance of the 1990’sTalk more about this laterTremendous improvement in HA fidelity and flexibility
Multiple channelsAllows separate frequency bands to be established and
processed (manipulated) separately and independently
Basic Componentsof a Hearing Aid
MicrophoneConverts sound waves to an electrical signal
AmplifierIncreases the amplitude of the electrical signal from the microphone
ReceiverConverts the amplified electrical signal back to sound
BatteryProvides power to drive the amplifier
Basic Hearing Aid Components
Putting everything togetherLet’s look at each of these components in a
little more detail…
BatteriesDrive the amplifierCome in about 6 sizes
denoted by a number675, 312, 13, 230, 10A, 5ASizes are not
interchangeable
Come in different materialsMercury (banned), silver
oxide, zinc-airMaterials can be used
interchangeable, but battery life might vary
Microphones
Two types are usedDirectional
Designed to respond primarily to sounds originating from in front of the wearer, not behind
Helps to improve S/N
Non-directional or omnidirectional
Equally sensitive in all directions
AmplifiersThe amplifier determines the “gain” of the
hearing aidHearing aid gain is the difference, in dB,
between the input level of an acoustic signal and the output level
Generally matched to the degree of hearing loss and the dynamic range of the listener
Also determines the method of output limitation and how the hearing aid increases intensity throughout it’s functional range
If the HA has a volume control, it is tied to the amplifier
Receivers
Most modern hearing aids use an internal air conduction receiver“G” You can’t see them
Other receiver options existBone conduction HAs
TraditionalImplantable (later)
Vibrotactile HAs(later)
Other CommonHearing Aid Features
On-off switchAllows the hearing
aid to be shut off completely
Battery saving deviceLevers, switches,
feature of the VCW
Other CommonHearing Aid Features
TelecoilSpecial circuit that enhances
telephone communication or allows compatability with loop systems (later)
Circuit emits an electromagnetic signal which is picked up by the t-coil
The t-coil signal is amplified and sent to the receiver
“D”
Other CommonHearing Aid Features
TelecoilTypically the user manually
activates the circuit“T switch”
M-T-OMT
Advantages to the telecoilReduces the occurance of
feedback when using the telephone
Improves the signal-to-noise ratio
Other CommonHearing Aid Features
Volume ControlDirectly tied to the
amplifier
Some HA styles don’t offer a VCW
CIC
Some DSP circuits don’t offer VC
These hearing aids continuously adjust the gain
Other CommonHearing Aid Features
EarmoldsSome hearing aid styles
require a separate earmoldBody HA, BTE, eyeglass HA
Serve three purposesDeliver the amplified sound
from the HA to the earCouples the HA to the wearerModifies the acoustics of the
amplified sound delivered to the ear
Here’s a diagram illustrating some common earmold styles
CD-ROM Ch07.06 and Ch07.07
Hearing Aid Fitting Considerations
There are three major considerations that that need to be addressed when making a recommendation of hearing aids:What hearing aid style will work best?What level of technology will work best?Monaural or binaural?
Hearing Aid Style
Currently, six styles are available from most manufactureresBody, eyeglass, behind-the-ear, in-the-ear,
in-the-canal, completely-in-the-canal
Nearly every level of technology is available in any style
Every degree of hearing loss can be fit appropriately with every style
Body Hearing Aid
AdvantagesHigh gain with no
feedbackLarge controls
DisadvantagesStigmaMonaural fitting only
Y-cordsMicrophone placement
Body baffle, clothing noise
Newer DSP circuits not available in this style
Eyeglass Hearing AidVery popular in the 1960’s-
1980’sNeeds an earmoldAdvantages
Used to be more cosmetically appealing, especially for people with unilateral HL
DisadvantagesFitting issuesBreakdown and repairTrue binaural fitting is not
possibleDSP circuits not available in
this style
Behind-the-Ear (BTE)
Needs an earmoldCD-ROM CH07.04
BTE
AdvantagesFlexibilityGood choice for kidsCompatibility with direct audio inputFew problems with feedbackMicrophone placementTrue binaural fitting possibleVery durable/good repair record
BTE
DisadvantagesStigma compared to custom stylesMicrophone placement compared to
custom stylesFit with glasses, etc..Harder to manipulate, compared to
custom styles
Custom Hearing Aid Styles ITE, ITC, CICAll components of the
HA fit completely in the pinna and/or EAM
Completely changed the approach audiologists take regarding the HA fitting
CD-ROM CH07.05
ITE and ITCAdvantages
Cosmetic appealEase of insertion/secure fitMicrophone placement is very realisticReduction in wind noise (especially
ITC)
DisadvantagesFeedback can be a problemBattery sizeExpense (especially as size decreases)Some desired options might not be
available in ITC Telecoil, directional microphones, VCW
Completely-in-the-Canal (CIC)
These hearing aids sit very close to the TM so the acoustic advantages are different than the other styles
The major drawback is that the listener needs a large enough earcanal to accommodate the minimum size the HA has to be
CICAdvantages
Easy to use and insertReduction/elimination of occlusion effectLess HA gain/reduction of feedback/phoneImproved localization abilityElimination of wind noiseElimination of cerumen problemInvisibleGreater high frequency emphasis is possible
DisadvantagesExpense, size, gain/output problems, custom
features not available
Level of Technology
There are currently three major levels of hearing aid technology people are able to access:Analog hearing aidsDigitally controlled analog hearing aids
Sometimes referred to as “programmable”
Digital hearing aids
Analog Hearing Aid
Oldest signal processing strategySignal is processed in a manner that’s continuously
varying over timeHere’s a schematic of an analog circuit
Hearing aid controls are analog, too
Digitally ControlledAnalog Hearing Aids
Uses analog signal processing with digital control over the electroacoustic parameters Gain, compression, frequency response, etc
Here’s a schematic of such a circuitMajor advantages include flexibility,
programmability, greater range of outputs
Digital Hearing Aids
Analog signal is converted to a digital representationOnce digitized, the signals are manipulated by
processing algorithms (programs) and converted back to analog form
Biggest advantage is complete flexibility and programmability
Here’s a schematic of a digital HA
Fitting One Ear or Two??
Benefits of binaural amplification1. Localization2. Binaural summation3. Elimination of head shadow4. Improved S/N through binaural
squelch5. Auditory deprivation
A Word AboutHearing Aid Maintenance..
This is mentioned specifically in the ASHA Scope of Practice for SLPs
Any client of yours wearing hearing aids needs to have their HAs checked dailyBattery
Invest in a battery tester
Earmold and receiver checked for wax
Recommended daily HA check proceduresHA troubleshooting guide