CSD 5400 REHABILITATION PROCEDURES FOR THE HARD OF HEARING Amplification Hearing Aids

Preliminary Remarks One of the most critical elements of any rehabilitation plan (child or adult) is the fitting of appropriate amplification This is the only recognizable way, at this time, to maximize residual hearing The 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 professional Audiologist Licensed hearing aid dispenser Hearing aids are the most common form of amplification, but not the only one

Selecting the Hearing 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 amplification Many 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 loss Lots of residual hearing Mild hearing loss Normal 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 MDs Lack of understanding of HL and HAs Financial 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 real Stigma 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 m/development.html

Recent Advances in Signal Processing Multiple memories Provides access to different amplification characteristics Increases flexibility Noise reduction circuits Sophisticated ways to improve the signal-to-noise ratio Major complaint of most listeners Feedback control Feedback is the audible signal related to an interaction between certain components of a hearing aid As hearing aids became smaller, feedback was a major limitation and complaint

Recent Advances in Signal Processing Programmability Allows the dispenser to set and control a number of different properties of the HA Increases “precision” of the fitting Increases hearing aid flexibility Digital processing Major tech advance of the 1990’s Talk more about this later Tremendous improvement in HA fidelity and flexibility Multiple channels Allows separate frequency bands to be established and processed (manipulated) separately and independently

Basic Components of a Hearing Aid Microphone Converts sound waves to an electrical signal Amplifier Increases the amplitude of the electrical signal from the microphone Receiver Converts the amplified electrical signal back to sound Battery Provides power to drive the amplifier

Basic Hearing Aid Components Putting everything together Let’s look at each of these components in a little more detail…

Batteries Drive the amplifier Come in about 6 sizes denoted by a number 675, 312, 13, 230, 10A, 5A Sizes are not interchangeable Come in different materials Mercury (banned), silver oxide, zinc-air Materials can be used interchangeable, but battery life might vary

Microphones Two types are used Directional 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

Amplifiers The amplifier determines the “gain” of the hearing aid Hearing 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 exist Bone conduction HAs Traditional Implantable (later) Vibrotactile HAs (later)

Other Common Hearing Aid Features On-off switch Allows the hearing aid to be shut off completely Battery saving device Levers, switches, feature of the VCW

Other Common Hearing Aid Features Telecoil Special 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 Common Hearing Aid Features Telecoil Typically the user manually activates the circuit “T switch” M-T-O MT Advantages to the telecoil Reduces the occurance of feedback when using the telephone Improves the signal-to-noise ratio

Other Common Hearing Aid Features Volume Control Directly 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 Common Hearing Aid Features Earmolds Some hearing aid styles require a separate earmold Body HA, BTE, eyeglass HA Serve three purposes Deliver the amplified sound from the HA to the ear Couples the HA to the wearer Modifies 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 manufactureres Body, 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 Advantages High gain with no feedback Large controls Disadvantages Stigma Monaural fitting only Y-cords Microphone placement Body baffle, clothing noise Newer DSP circuits not available in this style

Eyeglass Hearing Aid Very popular in the 1960’s- 1980’s Needs an earmold Advantages Used to be more cosmetically appealing, especially for people with unilateral HL Disadvantages Fitting issues Breakdown and repair True binaural fitting is not possible DSP circuits not available in this style

Behind-the-Ear (BTE) Needs an earmold CD-ROM CH07.04

BTE Advantages Flexibility Good choice for kids Compatibility with direct audio input Few problems with feedback Microphone placement True binaural fitting possible Very durable/good repair record

BTE Disadvantages Stigma compared to custom styles Microphone placement compared to custom styles Fit with glasses, etc.. Harder to manipulate, compared to custom styles

Custom Hearing Aid Styles ITE, ITC, CIC All 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 ITC Advantages Cosmetic appeal Ease of insertion/secure fit Microphone placement is very realistic Reduction in wind noise (especially ITC) Disadvantages Feedback can be a problem Battery size Expense (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

CIC Advantages Easy to use and insert Reduction/elimination of occlusion effect Less HA gain/reduction of feedback/phone Improved localization ability Elimination of wind noise Elimination of cerumen problem Invisible Greater high frequency emphasis is possible Disadvantages Expense, 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 aids Digitally controlled analog hearing aids Sometimes referred to as “programmable” Digital hearing aids

Analog Hearing Aid Oldest signal processing strategy Signal is processed in a manner that’s continuously varying over time Here’s a schematic of an analog circuit Hearing aid controls are analog, too

Digitally Controlled Analog 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 circuit Major advantages include flexibility, programmability, greater range of outputs

Digital Hearing Aids Analog signal is converted to a digital representation Once 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 amplification 1. Localization 2. Binaural summation 3. Elimination of head shadow 4. Improved S/N through binaural squelch 5. Auditory deprivation

A Word About Hearing 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 daily Battery Invest in a battery tester Earmold and receiver checked for wax Recommended daily HA check procedures HA troubleshooting guide