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Hearing Aid Audiology > Short Answer Questions > Flashcards

Short Answer Questions Flashcards

1
Q

is a body worn hearing aid? (BW)

A

Used for cx unable to manage controls of BTE or who cannot manage to place BTE over ear
Suitable for Poor VISION or DEXTERITY
Very rarely used
Suitable for mild to PROFOUND losses as high output levels are possible with less risk of feedback due microphone and receiver separated

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2
Q

What is bone conduction hearing aids?

A

Used if conventional aids unsuitable due to atresia or chronic infections
Suitable for CONDUCTIVE losses
Consist of bone conductor mounted on rigid headband to keep conducted in place.
Can be driven by BW or BTE aid
POOR COSMETIC appeal

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3
Q 
What are CROS hearing aids?
Contralateral 
Routing
Of 
Signals
A

Suitable for cx with SSD single sides deafness
Microphone on worse ear connected to receiver
Sounds then arriving at worse ear are transmitted to the receiver in better ear
worn on better ear with a OPEN fit.
Sound is NOT AMPLIFIED
can be wired or wireless
Advantages- sounds can be heard from either side,some patients able to localise sound due to differences in sound quality and timing of sounds arriving at ear
Disadvantages- if the hearing in the better ear is particularly GOOD wearer may find sound unacceptable

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4
Q

What is a Bi-CROS hearing aid?

A

Microphone worn on both ears with a the amplifier and receiver at the better hearing ear
Sounds arriving at BOTH EARS are AMPLIFIED

Disadvantage- signal from worse hearing side can reduce the clarity of the signal from the better side.

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5
Q 
What is a BAHA
Bone
Anchored 
Hearing 
Aid
A

Useful for conductive loses
Chronic ear infections
Malformation of pinna eg treachery Collins syndrome
There is aidable hearing only on one side

Operation performed to attach small titanium pin to the skull, when healed a box containing microphone and amplifier attached to pin.
Sound is delivered by bone conduction to both cochleas. Both cochleas respond to louder sounds and the better hearing cochlea quieter sounds

Ear level device suitable for BC loss of 45 dBHL
Body aid device up to BC 60 dBHL

Disadvantages- infections, growth of skin flap
Can’t restore true binaural hearing

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6
Q

What are cochlea implants

A

Operation performed to insert a chain of electrodes into cochlea, when healed sound processor is then attached. Sound from the processed is delivered electromagnetically to the electrodes which electronically simulate the hearing nerve.

Suitable for SEVERE to PROFOUND losses where aids provide little benefit
Cx with auditory neuropathy those who have good hearing but can’t understand speech

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7
Q

What is a middle ear implant?

A

Mechanical device surgically implanted in the middle ear
Improves hearing by vibrating the ossicles in response to sound

Suitable for those with mild to severe SNHL or mixed
Earmould allergies
Outer ear infections 
Malformed EAM
Excessive wax production 
Perspiration affection hearing aid use

Unsuitable for those with middle ear infections

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8
Q

Define linear amplification?

A

Gain remains CONSTANT no matter what the input level of the sound

There is a limit and tails of high levels

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9
Q

What is amplification?

A

Process of magnifying the sound signal

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10
Q

What is gain?

A

Difference between the input level dbSPL and output level = gain

GAIN = OUTPUT - INPUT

Gain measured in dB

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11
Q

What is
FREQUENCY RESPONSE
of a hearing aid?

A

When hearing aids can be programmed to vary the gain they give at each frequency.
Normally shown on graph of free and gain
Use right sided axis in dB

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12
Q

What is maximum output

A

It’s the maximum amount of output a hearing aid can produce.
Can be shown on graph with curve
Measured in dBSPL
Measured using left axis

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13
Q

What is harmonic distortion?

A

Occurs when additional frequencies of sound which where not present in the input to the hearing aid are then measured in the aid output
Usually shown as table by test in test box distortion should be no more than 10%

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14
Q

Benefits of binaural hearing?

Aids?

A 
BSA 2017
Improved speech understanding in noise
Improved localisation 
Reduced listening effort
Prevent auditory deprivation of unaided ear as stimulates both hearing pathways
Can reduce tinnitus 
Evidence of patient preference
Guidelines recommend offering two unless contraindications present
Can be cost effective
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15
Q

Name two types of couplers used in measuring hearing aid output in test box?

A

Ear simulator (IEC711)- has main cavity and several side cavities of different sizes. Used to mimic acoustic properties of ear

2CC coupler- repeatable way to monitor microphone (used mostly in clinic) not great for measuring ear properties

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16
Q

List the three tests usually performed by test box?

A

Reference test gain
Frequency response
Harmonic distortion
Internal noise

Can measure attack and release times with aids that have compression.

???Full on gain
Maximum output SSPL
OSPL

Measures pure tones (maximum output) sweeps frequencies.

Broadband noises

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17
Q

Why might people with the same audiogram get different results from hearing aids?

A

Frequency discrimination
Temporal elements
Central processing

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18
Q

When is a unilateral hearing aid fit appropriate

A

Poor dexterity (unable to handle 2 aids)
The patient does not want them
Patient has diplacusis (difference in pitch perception between ears)
One ear has much poorer speech discrimination

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19
Q

What is the 50dBHL guide for fitting aids

A

Judges what ear to amplify if only aiding one ear

The PTA closest to 50db is aided for best results

Used in absence of any other pre determine factors such as cx preference

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20
Q

What is peak clipping?

A

A basic form of output limiting in linear amplification
Clips peaks of waveform when to loud
Reduces loudness to that within cx dynamic range
Disadvantage: introduces distortion into waveform

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21
Q

Describe the three main STATIC characteristics of compression

A

Compression RATIO- describes the reduction in gain caused by the compressor

Compression THRESHOLD- the at which compression starts act on signal

Compression KNEEPOINT- the SPL at which the compression ratio changes

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22
Q

Define dynamic characteristics of compression

What are the key two characteristics?

A

How Quickly the compression operates

ATTACK TIME (time it takes for aid to activate compression after change in input/output)

RELEASE/RECOVERY TIME(the finite time taken for aid to deactivate compression following change in input/output)

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23
Q

What is comfort compression?

A 
Makes MODERATE and LOUD sounds more comfortable 
Moderate kneePoint 
Low compression ratio (eg4-1)
SLOW activation times
INPUT controlled
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24
Q

What is syllabic compression?

A

reduces the loudness contrasts between different elements of SPEECH
Designed to reduce syllabic contrast in intensity of the signal (e.g. Increased gain for low intensity sounds decreased gain for high intensity sounds like vowels)
Frequency dependent
Input controlled
FAST acting and releasing
KneePoint at moderate level

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25
Q

What is output limiting compression?

A

Stops sound exceeding ULL’s
Reduces distortion at high sound levels
QUICK ACTING
OUTPUT controlled
Usually high kneePoint (eg10-1)
Similar function to peak clipping but better as much less distortion
Important for severe to profound hearing losses

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26
Q

Name three ways compression can be used to help hearing aid wearers

A

Can help people with reduced dynamic range

Can help conductive losses by output limiting prevents hearing aid going into saturation and distorting the signal.

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27
Q

What is the compression threshold?

A

The WHEN of compression-The point on the input/output function at which output is 2db lower than if no compression had occurred.

28
Q

What is the compression kneePoint?

A

The point at which the compression ratio changes
Common to have more than one
Compression threshold is kneePoint

29
Q

In dynamic compression attack times can be fast acting or slow acting, explain?
What is usual attack and release time?

A

Fast acting- attack/release times are SHORT useful for speech
slow acting- arrack/release times are LONG useful for comfort

Attack times usually 5-50ms
Release times usually20-500ms or greater
Some compressors have ADAPTIVE release times which change according to duration of the increase in input.

30
Q

What is the compression ratio and how does this affect hearing aids?

A

Hearing aids use CR 10-1

31
Q

What is input and output compression?

A

Input-detected is located on the input side BEFORE volume control
Gain/output increased
KneePoint remains the same

Output-detector located on output side AFTER volume control
Volume effects gain and kneePoint but not MPO

32
Q

What is Wide Dynamic Range Compression

A

Makes the most of the dynamic range for each person
Maintains loudness relationships in complex sounds
Low kneePoints
Fairly low compression ratio (eg2-1)
Input controlled
Usually has multiple channels
Aims to restore loudness in moderate sounds- best for moderate losses

33
Q

What is expansion in relation to compression

A

Opposite to compression
Softer sounds amplified less than loud ones
Useful forHL with good low frequency hearing and moderate loss mid/high that hear internal noise through aid
Those who find low level background noise distracting
Bad point - hearing speech in low level noise is affected.

34
Q

What is NAL-NL1 fitting

A

National
Acoustic
Laboratories 2001
Based on loudness of speech

35
Q

What is DSL fitting formulae?

A

Desired
Sensation
Level

36
Q

What is RECD?

A 
Real
Ear to
Coupler
Difference 
Looks at how well a signal responds in a real ear compared to a 2CC coupler measured in dBSPL

Quick to perform
Can adjust hearing aid without patient being present

37
Q

What is a SPL-ogram?

A

A graph on Wichita dB scales are converted into identical units dBSPL, shows:
Normal thresholds
Patient thresholds
Long term average speech spectrum (LTSS)
Used to display target outputs for hearing aids.

38
Q

What are the two types of distortion?

A

Harmonic distortion- single frequency input to aid resulting in undesirable additional related frequencies. Only occours at frequencies greater than input signal. THD total harmonic distortion expressed as percentage

Intermodulation distortion
Two frequencies presented simultaneously output contains more can be above or below input.

39
Q

What is the compression ratio?

A

When signal loud enough to activate kneePoint the compression ratio determines how much signal will be compressed

CR=input/output

Converted into ratio as eg 1.1

40
Q

What is the attack time?

A

AT is the delay that occours between onset of an input signal loud enough to activate compression i.e. Input signal exceeds the TK

41
Q

What is the release time?

A

DELAY between onset of signal and input signal falls below the TK

Generally longer than attack times
RT of 20ms considered fast

42
Q

Name digital signal processing features of hearing aids that we can use to help patients?

A

Better fit to audiogram by:
Multichannel hearing aids
Multiple compression ratios e.g. Dynamic compression and expansion

Improved SNR by:
Directional microphones
Noise reduction
Feedback cancellation

43
Q

What different types of outcome measures do we use in audiology

A

Patient orientated-
Assess patients needs
Assess effectiveness of rehabilitation
Asses need for further help

Service orientated
Evaluate service
Evaluate changes to service

44
Q

Name three types of outcome measures and examples of each?

A

AUDIBILITY
Aided thresholds
Speech tests

TECHNICAL OUTCOMES
Real ear measurements

SELF REPORT QUESTIONARIES
Hearing aid benefit 
Satisfaction with aids
QoL 
Satisfaction of services
45
Q

Name two types of questionnaires used to measure outcomes and what are benefits and disadvantages of these

A

GLASGOW PROFILE
COSI
benefit

Disadvantage

Some cx can’t complete as lack comprehension

46
Q

What are the benefits of open jaw impressions?

A

Provides largest ear canal volume
Resulting moulds and ITEs secure
Useful for fitting instruments that need high gain
Suitable for CIC
Useful when cx had had retention problems
Enhanced acoustic seal for feedback

Disadvantages
Material for mould must be soft
Can be costly as need both open/closed impressions to be taken

47
Q

What are the materials earmoulds can be made from?

A 
Hard acrylic (easy to modify)
Soft acrylic (improved acoustic seal and comfort)
Silicone ( non allergenic) improved acoustic seal
Micro flex (non allergenic)
48
Q

Explain acoustical effect of using vents?

A

Comfort vent- allows aeration of the ear canal- mild/moderate 1mm
Acoustic vent- reduces the low frequency gain.
Essential when patient has good low frequency hearing
Needs to be 2mm to be effective
Increases risk of feedback

49
Q

Explain acoustical effect of using filters?

A 
Dampeners 1-3khz
used to smooth peaks in response 
Can alter gain in mid frequencies 
Comes in different strengths 
Filters placed closest to moulds reduce peaks
Can collect debris block sound
Can reduce feedback
50
Q

Describe acoustical effects of using horns

A

Change in size of tubing
Increases HIGH frequency gain above 300hz
Usually 3-4mm Libby horns used

Reverse Libby horn does opposite

More expensive

51
Q

Describe the term occlusion effect?

A

O and E more noticeable

Patient with low frequency thresholds better than 40db more likely to have occlusion affect

52
Q

What is signal processing technology in hearing aids?

Give examples

A 
Signal processing is anything that manipulates the sound signal including
Amplifying
Filtering
Peak clipping 
Compression, WDRC etc 
Frequency lowering
Anything else where SIGNAL changed
53
Q

How does digital processing in hearing aids allow for a befit of audiogram?

A

Multichannel- can have up to 20 bands allowing adjustments for more specific frequencies

Multichannel compression ratios including dynamic compression and EXPANSION

54
Q

What features of digital signal processing in hearing aids can improve SNR?

A

Directional microphone systems
Noise reduction
Feedback cancellation

55
Q 
What is BILL and when is it used?
Base
Increases at
low
Levels
A

Aim- to provide good listening for speech in BACKGROUND noise
Used for cx with significant LOW FREQUENCY LOSS
Low frequency background loss compressed more than high frequencies so that speech CLARITY cimproves
Low kneePoint for low frequencies
Higher kneePoint for higher frequencies

56
Q 
What is TILL and when is it useful in hearing aids?
Treble
Increase at
Low 
Levels
A

Is type of WDRC that affects HIGH frequencies
Aim- to stop sounds exceeding ULL’s were wearer has reduced dynamic range
Suitable for mild/moderate loss reduced dynamic range in high frequencies
HIGH frequencies compressed more than low, ensuring output stays within DR
High kneePoint for low frequencies
Low kneePoint for the high frequencies

57
Q

What is expansion in hearing aids?
What are its uses and benefits
What is its disadvantages?

A

Opposite to compression
Gain increases as input level increases
Softer sounds are amplified less than loud ones
Used for- cx with GOOD LOW frequency hearing and moderate loss at mid and high
That hear INTERNAL noise from hearing aid
People that find background noise distracting
Negative- speech in low level noise is affected

58
Q

How can hearing aids use digital sound processing to achieve noise reduction for cx?

A

SPECTRAL SUBTRACTION
eliminates the frequency spectrum of noise and subtracting from speech spectrum
If noise overlaps the speech spectrum too much then some of the speech signal will be lost

PHASE CANCELLATION
Measures exact waveform of noise and cancels by producing identical but reverse phase 180 degree phase to original sound
Difficult to measure exact waveform of noise due to competing speech therefore some speech signal may be lost
High battery needed

COMPRESSION
Applied long term to moderate to loud low frequency sounds

SPEECH SYNTHESIS
an algorithm detects speech cues in background noise
Adds artificial speech sounds to the detected sounds to enhance recognition
Can be issues where background noise consists of speech
Speech can sound unnatural

59
Q

What is noise reduction in hearing aids?

A

Process of reducing and eliminating the noise that the hearing aid wearer doesn’t want to hear

Most use spectral subtraction assuming background noise is low frequency

Some use spectral enhancement

When applied noise reduction reduces wearers ANNOYANCE and can sometimes improve SPEECH RECOGNITION

60
Q

How do digital hearing aids detect feedback and achieve feedback cancellation

A

Types of feedback detection
Static-at initial switch on
Dynamic-Continuous monitoring

NOTCH FILTERING
Reduces gain in narrow frequency range
Uses filters to reduce gain at which frequencies feedback occurs.
Can be static: aid sets running check and identify bands where feedback occurs. Unfortunately frequency of feedback changes so there is limitation to static notch filtering
or active: aid continuously monitors its output for feedback if identified aid creates a notch filter at the appropriate frequency
Active more effective however can be slow to adapt to change in noise

PHASE CANCELLATION
Produces sound in reverse phase to the noise.
Works by-Microphone picks up feedback, Processor reverses feedback by 180 degrees. Transducer emits reverse signal.
Dependent on processing power of aid and battery life to be effective
Can remove several feedback tones at the same time without this affecting the quality of speech sound

61
Q

Explain benefits uses of directional microphones and how these can be enhanced by digital signal processing?

A

Directional microphones increase SNR by picking up more sound from front of hearing aid than other directions.

Digital signal processing can enhance performance by
control shape of POLAR plot
Automatically switch between directional and omnidirectional modes.

Microphones can also be FREQUENCY directional
Processing of aid must be fast for this

62
Q

What are dead regions?

How to aid?

A

There is no benefit from the amplification in the dead region because of the hair cell death

High levels of gain applied in dead regions can reduce frequency discrimination for other sounds

Tend not to amplify to prevent further damage to auditory system

63
Q

What is frequency lowering used for in hearing aids

What cx suitable for

A

Moves high frequency sounds to a lower frequency to improve their audibility

Can be helpful in precipitous drop loss. Where hearing is severe to profound in high frequencies however good hearing in mid frequencies
However results can vary between cx some find good others don’t like, not enough research.

64
Q

Why would you use REM’s

A

Prescription formula is general
REMs verify is correct at all frequencies
Sound at target at TM
Takes into account cx own ear canal shape, resonance
Quick and easy to conduct

65
Q

What is classed as a good fit for a REM ?

A

+or - 5 dB

At frequencies between 250-6kHz

Hearing Aid Audiology (2 decks)

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