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