– Most conductive losses are medically or

surgically treatable

– Examples: Cerumen impaction, acute otitis media, chronic otitis media, perforated

eardrum

– People with permanent CHL do very well with hearing aids

• Some people may use a bone conduction aid

– Most sensorineural hearing losses are sensory, not neural

• Problem in cochlea

• Frequently, the outer hair cells

– Outer hair cells are extremely vulnerable to insult

– Degree of hearing loss tends to be related to the amount of hair cell damage

 • The greater the degree of hearing loss the more likely OHC and IHC are involved.

Most with sensorineural losses benefit from hearing aids (depending on degree)

– Amplifying the signal overcomes the sensitivity loss due to hair cell damage

miniature amplifiers

– Capture incoming sound, increase its intensity, and deliver it to the ear

– Body-worn

– Behind-the-ear (BTE)

- Open-fit BTE

– In-the-ear (ITE)

– In-the-canal (ITC)

– Completely-in-the-canal (CIC)

– Bone conduction hearing aids 

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– Less focus on miniaturization, more focus on improving performance

– Holy grail of hearing aids: Improve speech perception in noise

• Changes in signal processing technology

• Changes in microphone technology

– New in 2005

– Key ingredients

• Fitted to ear with narrow tube

• Digital feedback cancellation

– Excellent for high-frequency hearing losses

– Have led to large increase in BTE sales

• Jump from 25% to approx. 50% in 2007

1. Sound is picked up by the microphone

– Converts acoustic signal to an electrical signal

2. This electrical signal is then amplified and/or processed in some way

3. The receiver converts the electrical signal back to an acoustic signal

– In a BTE, sound is delivered to the ear canal by the earmold

Three main types of processors or circuits

1. Analogs

2. Digital

3. Hybrid or “digitally programmable”

– Sound is processed as a continuous electrical signal (generated by the microphone)

– Signal is modified by electronic components

– Hearing aid characteristics are adjusted by screw settings

Analog

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– Electrical signal from mic is converted into 1’s and 0’s

– Computer chips carry out the various signal modifications

– Characteristics are programmed using specialized software

– Can store multiple sets of characteristics

– First true digital hearing aids debuted in 1998

Digital

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Hybrid or “digitally programmable”

– Sound remains in analog form

– Electronic circuits modify the signal

– However, hearing aid settings are controlled using computer software and stored in the hearing aid digitally

– Can have multiple settings stored

– Debuted around 1990

Hybrid

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Hearing Aid Characteristics

– Gain

– Frequency response

– Input/output function

Hearing Aid Components

– Microphone

– Amplifier

– Receiver

- volume control wheel

- batter

- telecoil

• Automatic volume control

• Multiple memories

– Can have different internal settings for different listening environments

• Remote control

– For controlling volume, or switching between programs

• Earmold material (for BTE)

– Hard or soft; hypoallergenic

• Telecoil

– Everyone should have one

• Directional microphone

– May improve speech understanding in noise

Problem with both of these: the switch

– May be too complex/hard to manipulate for some people

– Some companies offer automatic switching for directional microphone

– Gain

– Frequency response

– Input/output function

– Microphone

– Amplifier

– Receiver

- volume control wheel

- battery

- telecoil

• The difference in dB between the output and the input

• This is how much amplification the hearing is providing

• Specified in dB:

– Gain = Output level – input level

• The more severe the hearing loss is, the more gain you need

• Prescriptive formulas are often used to determine how much gain a given patient should have at each frequency

– Try to make sounds audible but comfortable

– Many approaches available

A description or graph of how gain varies as a function of frequency

• Can be adjusted several ways

– Analog hearing aids have screw pots on the faceplate of the hearing aid

– For digital and hybrid instruments, the response is programmable

• Ideal goal: Maximize audibility of speech

– Some formulas use the Articulation Index to prescribe gain

- we don't need to provide gain in frequencies that they can hear

- hearing aids have a hard time amplfying things >4000Hz

Input-output (I/O) function

Shows how hearing aid output changes as a function of input level

have constant gain for all input levels (to some max. output)

gain varies depending on input level

• Low-level sounds are amplified more (they get more gain) than high-level sounds

• Special prescriptive formulas have been developed for nonlinear hearing aids

– They set the I/O characteristics based on the patient’s loudness growth function

• Measured using rating scales

– Goal: Make speech audible but never uncomfortable

• Microphone – options:

– Omnidirectional

• Single microphone, picks up sound equally well from all directions

– Directional (2 or more microphones)

• Designed to give strongest response to sounds in front of the wearer

• The best way to improve speech understanding in noise w/ a hearing aid

• May have a switch or be automatic

• Amplifier (or processor)

– Can be analog or digital, linear or nonlinear

• Receiver

– Converts electrical signal back to an acoustic signal for delivery to ear

• Volume control wheel

– User can adjust gain as desired

– Nonlinear aids do this automatically – often called automatic gain control (AGC)

• Battery

– Usually the largest part of the hearing aid

• Telecoil

– Picks up magnetic signals

• From an analog telephone

• From an induction loop

– Around a room

– Around the neck

- User switches aid from “M” to “T”

– Candidacy

– Type/style of hearing aid

– Hearing aid features

– Monaural vs. binaural fitting

– Expectations

– Medical clearance (referral or waiver)

– Loudness growth measures

– Earmold impressions

– Pre-testing for later validation

• Soundfield testing

• Speech in noise

• Questionnaires

What determines candidacy for a hearing aid?

- Whether they are handicaped by the hearing loss

- Whether they will benefit from hearing aids

- Whether they wan hearing aids

• Selection involves matching hearing loss with:

– Communication needs

– Style

– Technology

• Type, degree, and configuration of hearing loss are the most important determinants of

– the style and features of HA

– type of signal processing

– Required gain and desired features

• The larger the hearing aid, the greater gain and more features you can get

– Physical condition of outer ear

• Including size, cerumen production, skin sensitivity

– Cosmetic concerns

– Financial concerns

• Average prices by technology

(2005):

– Digital = $2022

– Analog = $935

– Better sound localization

– Binaural summation

• It’s easier to hear with two ears than with one

– Improved speech recognition in noise

– More natural sound quality

– Avoid auditory deprivation effects

– Asymmetrical hearing loss

– When one ear is not a candidate for some reason

• Poor word recognition abilities

• Physical status

– Mild hearing loss

• Binaural benefits increase as hearing loss gets more severe

– Is the hearing aid doing what it’s supposed to be doing?

– Verify using electroacoustic analysis in a hearing aid test box

• Compare to manufacturer specifications

• Pre-adjust hearing aid settings to meet prescriptive targets for gain and output

Fit the hearng aid using real-ear measurements

– Measure sound @ eardrum without the hearing aid, then with the hearing aid

– Adjust the hearing aid to meet prescriptive targets and achieve good sound quality

– Measure aided pure tone thresholds in the soundfield and compare to unaided

– Functional gain = difference between these two measures

– NOT RECOMMENDED as replacement of Real Ear

• Can also use speech measures to verify performance

– Quality judgments

– Recognition abilities (in Q and N)

• Other things to check:

– Aid fits securely in the ear

– No feedback at desired volume setting

– Comfort

• Should never have to “break it in'

– Patient can insert and remove

– Patient can manipulate volume, battery, any switches

– Cosmetic appeal

Patient needs a realistic picture of what to expect from hearing aids

• Reasonable goals:

– Significant benefit (i.e. aided better than unaided) in both quiet and noise

• Note, noisy conditions will always be harder than quiet conditions

– Soft sounds are “soft but audible”, average sounds are “comfortable”, loud sounds are “loud but not uncomfortable”

• Reasonable goals:

– Comfortable physical fit

– One’s own voice should sound acceptable (no occlusion effect)

– No feedback when aid is placed properly in ear, at a comfortable volume

• Patient must communicate with dispenser if any goals aren’t met

– Can fix the problem

– Can return the aids for a refund

– insufficient amplification/gain

• 80 dB gain at 1 KHz vs. 80 dB gain at 4 KHz,

– acoustic feedback,

• In high gain aids or ITE aids

– distortion of spectral shape and phase shifts,

• Best gain in 500 Hz to 2000 Hz region (miss lows and highs)

– nonlinear sound distortion,

• With high level output can get distortions

– occlusion effects,

• Tight seal = uncomfortable, pressure, aural fullness

– cosmetic appearance,

– abnormalities in the ear canal prevent use of a conventional hearing aid

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A, Conventional air-conducting hearing aid.

B, Implantable aids with piezoelectric actuator

(e.g., Rion-E, Otologics MET, and Implex TICA).

C, Implantable aids with piezoelectric sensor and

actuator (e.g., St. Croix Envoy).

D, Implantable aids with magnetic actuator (e.g.,

Vibrant Med-El Soundbridge, Soundtec DDHS).

E, Bone-anchored hearing aid (e.g.,

Cochlear/Entific BAHA). EAC, external auditory

canal; TM, tympanic membrane.

• Use for conductive losses

– Chronically draining ears

– Discomfort from levels with traditional HAs

– Large mastoid bowl or meatoplasty

– Otosclerosis

– Tymplanosclerosis

– Canal atresia

• Implantable middle ear hearing aids (like conventional HAs) employ a microphone and a signal processor that amplifies and alters the sound signal

– The implantable middle ear hearing aids convert the

electric signal into a mechanical energy that is coupled directly to the ossicular chain.

• Piezoelectric Transducer

– Ossicles are connected to an amplifier using a piezoelectric crystal vibrator.

• Electromagnetic transducer:

– generates a magnetic field (via a coil) that carries a current

• in turn this encodes the output of the microphone

– do not directly contact the ossicular chain

– rely on electromagnetic transmission to a unit that is

attached to the ossicles (smaller unit, more distortion free amplification)

The Otologics MET (Middle Ear Transducer)

– Uses peizoelectric transducer

– Original MET was semi-implantable

– Now it is fully implantable marketed as the Carina

– uses a subcutaneous microphone rather than an external microphone

– Phase I trial results in the United States showed 10 to 20 dB of functional gain across audiometric frequencies at 3 months postoperatively

– Pure-tone bone averages were minimally changed from preoperative values.

– Some poorer performance initially with device compared to conventional HAs

– Greater subjective benefit