Hearing instruments Flashcards
1
Q
What are the two main reasons why hearing aids are the main focus of management for hearing loss?
A
- They are cost effective
- Research shows benefit
2
Q
What kind of hearing aid is depicted in this image?
A
Behind-the-ear (BTE) hearing aid - delivers sound through an earpiece
3
Q
What is the difference between a classic BTE and a life tube BTE?
A
A classic BTE delivers sound through an individually made earmould whereas a life tube BTE uses BTE units but delivers the sound to the ear using a tinner tube and smaller earpiece
4
Q
What are the advantages of BTE hearing aids?
A
-They can be fitted to a wide range of hearing losses from mild to profound
-Can be exchanged very quickly if hearing aid breaks
-More reliable with fewer repair problems
-Easy to clean
-Larger batteries mean more power is available for extra features
5
Q
What are some of the disadvantages of BTE hearing aids?
A
-Appearance more often a concern
-Some wearers have difficulty inserting earmoulds
-Susceptible to wind noise
6
Q
What are the advantages of a life tube BTE compared to a classic BTE?
A
-More cosmetically appealing
-Good for people who have good hearing at some frequencies; delivers amplification at the required frequencies whilst allowing natural sound into the ear
-Does not occlude the ear and is more comfortable
-Some wearers find the tube easier to insert than an earmould
7
Q
What are the disadvantages of a life tube BTE compared to a classic BTE?
A
-Some wearers find the tube too small to feel when holding the hearing aid
-Some wearers find the aid can fall out more easily with this type of fitting
8
Q
What kind of hearing aid is depicted in this picture?
A
Receiver-in-the-ear (RITE) or receiver-in-the-canal (RIC) - hearing aid sits behind the ear and delivers sound through a small speaker (receiver) which is attached by a small wire and placed in the ear canal
9
Q
What are some advantages of RIC hearing aids?
A
-Small and lightweight
-Less prone to feedback
-More natural sound due to open ear canal
10
Q
What kind of hearing loss are RIC hearing aids used for?
A
Mild to moderate hearing loss
11
Q
What is the disadvantage of RIC hearing aids?
A
Receiver end is vulnerable to moisture in the ear canal therefore frequent repairs are often required
12
Q
What is the difference between standard and custom hearing aids?
A
Standard hearing aids are generic where the settings and earpiece can be modified to personalise the fitting to the wearer’s ear and hearing loss, whereas custom hearing aids are tailored to the wearer’s ear
13
Q
What type of hearing aid is depicted in this picture?
A
In-the-ear (ITE) hearing aid - sits in the ear and fills the concha, is made uniquely to fit the wearer’s ear
14
Q
What are some advantages of ITE hearing aids?
A
-Some wearers prefer their appearance
-Very easy to insert into the ear
-Very easy to use with telephone
-Less sensitive to wind noise than BTE devices
15
Q
What are some disadvantages of ITE hearing aids?
A
-Higher initial cost than BTEs
-Must be returned to the manufacturer for repairs
-Expensive to remake if lost or damaged
-Size limitation sometimes makes direct input and telecoil options unavailable
-Manipulating user controls may be difficult for patients with diminished manual dexterity
16
Q
What type of hearing aid is depicted in this image?
A
In-the-canal (ITC) - hearing aid sits in the outer portion of the ear canal (smaller version of ITE)
17
Q
What are some of the advantages of ITC hearing aids?
A
-Improved appearance compared to BTEs and ITEs (much less visible)
-Easy to use with the telephone
-Less affected by wind noise than BTEs
18
Q
What are some of the disadvantages of ITC hearing aids?
A
-Cost
-Size limits space for electronics and reduces the range of features available (e.g. telecoil and directional microphones usually not possible)
-Must be returned to the manufacturer for repair if faulty
-Small size means that some wearers have difficulty inserting the hearing aid or using the controls
19
Q
What type of hearing aid is depicted in this picture?
A
Completely- in-the-canal (CIC) - hearing aid sits inside the ear canal, custom made to fit the wearer’s ear
20
Q
What kind of hearing loss are CIC hearing aids appropriate for?
A
Mild to moderate hearing losses
21
Q
What are some advantages of CIC hearing aids?
A
-Reduced risk of feedback (unless vented)
-Improves sound localisation
-Less gain required because the hearing aid is nearer to the eardrum
-Elimination of wind noise
-Enhanced telephone use
-Virtually invisible
-Greater high frequency gain achievable
22
Q
What are some disadvantages of CIC hearing aids?
A
-Costly
-High maintenance devices as they can easily be damaged by wax and condensation from the ear canal
-Cerumen/ ear wax build up means frequent cleaning is necessary
-Size limitation means some features are unavailable e.g. direct audio input, telecoil, directional mics
-Small size limits battery size and hence the power of the hearing aid
-May cause occlusion effect
23
Q
What type of hearing aid is depicted in this image? What are some special considerations associated with this type of hearing aid?
A
-Extended wear hearings aid
-Must be inserted deep into the ear canal by a specially trained audiologist or ENT doctor
-Worn for 24 hours a day
-Battery lasts up to 120 days
-Expensive (requires subscription)
-Tiny size means no additional features
24
Q
What are body worn hearing aids?
A
-Microphone and amplifier are housed in a small box which is clipped to the clothes or put in a pocket
-The sound is delivered to the receiver via the lead
-The receiver is held in place in the ear by an earmould
25
Who are body worn hearing aids particularly useful for?
-Individuals with poor vision or dexterity, who cannot manage the controls of a BTE hearing aid or cannot manage to place the BTE over their ear
-Suitable for mild to profound losses as high output levels are possible with less risk of feedback because the microphone and receiver are separated
26
Who may bone conduction hearing aids be suitable for?
Conductive hearing losses if conventional hearing aids are unsuitable e.g. atresia, chronic ear infections
27
Why are BC hearing aids rarely used?
They have poor cosmetic appeal and can be uncomfortable
28
What type of BC hearing aid is depicted in this picture?
-Headband
-BC hearing aid is attached to a hard band that sits behind the ear and applies pressure to the skull
-Sound is delivered when the hearing aid vibrates the headband which in turn vibrates the skull
-This vibration is interpreted as sound by the cochlea
29
What kind of BC hearing aid is depicted in this picture?
-Soft band
-The BC hearing aid is attached to an elasticated band which goes around the head and applies pressure to the skull
-Sound is delivered when the hearing aid vibrates
30
What kind of BC hearing aid is depicted here? Who are these hearing aids useful for and what are their disadvantages?
-BC hearing aid is attached to or integrated into a pair of glasses
-Sound is delivered when the hearing aid vibrates through a thin tube or receiver in canal
-BTE hearing aids are incorporated into the frames
-Useful for people with moderate to profound losses and vision problems
-However can be costly and the whole unit must be returned to the manufacturer for repairs or replacement lenses/ hearing aids
31
What are contralateral routing of signal (CROS) hearing aids?
-For patients with "single sided deafness" (severe to profound unilateral sensorineural hearing loss and normal/ mild hearing loss on the other side)
-Microphone is worn on the worse ear, which is wirelessly connected to a receiver worn on the better ear with an open fitting so that the wearer can hear sounds on the better side
-Sounds arriving at the worse ear are transmitted without amplification to the receiver in the better ear
32
What are bilateral contralateral routing of signal (BiCROS) hearing aids?
-Used for patients with severe to profound sensorineural hearing loss where there is also a degree of hearing loss in the better ear
-Microphone worn on the worse ear which is wirelessly connected to a receiver on the better ear
-Sounds arriving at both ears are amplified before being delivered to the better ear
-Combining both signals can result in clarity problems
33
Name the four types of implantable devices
1. Middle ear implants
2. Bone-anchored implants
3. Cochlear impants
4. Auditory brainstem implants
34
What are middle ear implants?
-A transducer is attached to the incus or stapes in the middle ear
-The sound processor collects and amplifies the sound and then transmits the signal to a receiver under the skin which causes the transducer to increase movement of the ossicles
35
What are bone-anchored implants?
-Titanium pin is surgically inserted into the mastoid bone in the skull
-Once the pin has integrated with the bone a sound processor is attached
-The device amplifies sound and transmits it to the cochlea by vibrating the pin and the skull
36
What are cochlear implants?
-Surgically implanted prosthetic device
-An array of electrodes is attached to a receiver is inserted into the cochlea and the receiver is implanted under the skin behind the ear
-Once healed, a sound processor is attached externally and delivers amplified sound to the cochlea
37
What is an auditory brainstem implant?
-A surgically implanted prosthetic device similar to a cochlear implant which delivers the electrical stimulation to the cochlear nucleus in the brainstem rather than the cochlea
38
What is the main function of a hearing aid?
To amplify the frequency range most important for understanding speech
39
What is the function of the hearing aid microphone?
To collect the sound signal and convert it into an electrical signal
40
What is the electrical signal converted to?
Digital signal which is manipulated by a speech processing algorithm and amplified
41
What happens to the signal after amplification?
It is converted back to an acoustic signal by a receiver and delivered to the person's ear via an earpiece
42
How do modern hearing aids work to amplify sound and how does this differ from traditional analogue hearing aids?
-Modern hearing aids separate sound into 48 frequency bands and amplify each band by a specific amount to restore hearing to normal or near normal levels
-Digital hearing aids offer a more natural and rich sound than analogue hearing aids because they are better at matching the wearer's unique hearing loss
43
What is the role of the pre-amplifier?
To make the electronic signal louder
44
What is the role of the analogue-to-digital converter?
To change the electronic signal into a digital signal
45
What is the role of the digital signal processor and the digital-to-analog converter?
The digital signal is processed by a digital signal processor and changed and converted back into analogue signal by the digital-to-analogue converter
46
What is a transducer? What are the two main types of transducers in hearing aids?
-A transducer is a device which changes energy from one form to another
-In a hearing aid these are microphones (input transducers) and receivers (output transducer)
47
What kind of microphones are usually used in hearing aids?
Elecret microphones
48
How do electret microphones work?
1. Sound pressure waves enter the front of the microphone through the acoustic entry port
2. Diaphragm oscillates
3. Oscillating voltage created between diaphragm and the backplate which is transmitted through to the pre-amplifier
49
What are the common issues with hearing aid microphones?
-They have internal noise due to components of the electrical circuit
-Wind striking the microphone causes noise
-Easily damaged by debris and often manufacturers will cover the microphone to protect them from this
50
Which factor determines the output of the receiver?
Its size
51
How do hearing aid receivers work?
-Alternating current causes the armature to vibrate between two magnets
-The armature movement causes vibration of a diaphragm or plate
-Diaphragm movement creates sound pressure waves which we hear as sound
52
What are some common issues with hearing aid receivers?
-Easily damaged by debris
-Easily damaged by dropping
-May continue to work but could be distorting which means the quality of sound can deteriorate over time
-Receiver vibrations can lead to vibratory feedback (repeated amplification of internal oscillations within the hearing aid) ~ solved by having a RIC
53
What does having a digital amplifier allow for?
-Less internal noise
-Less distortion
-Great shaping flexibility of incoming sound
-Ability to perform changes in the frequency response e.g. noise suppression, feedback management
54
What is the Telecoil?
-Contained within the hearing aid
-An amplifier converts sound signals into an electromagnetic current which is delivered along a loop of wire
-If the hearing aid wearer is located within the loop system range the T-coil detects the electromagnetic signals, amplifies them, and converts them to sound
-This improves signal-to-noise ratio
55
What is a disadvantage of the Telecoil?
It is prone to interference
56
What kind of batteries do hearing aids usually use?
Mostly zinc/air which are not rechargeable and start to self-discharge at a low rate once the seal is broken
57
What are the advantages of rechargeable hearing aid batteries?
-Easy to use as don't have to manipulate small batteries on a daily basis
-Environmentally friendly
-Cost-effective
-Convenient as you do not have to remember to buy new batteries
-Safer as they are less likely to be swallowed by babies or dogs
58
What are the disadvantages of rechargeable hearing aid batteries?
-Replacement is inconvenient
-More expensive
-Must charge daily
-Limits hearing aid styles
59
Label the components on this BTE hearing aid starting from the top and moving to the right
1. Hook
2. Tubing
3. Earmould
4. Rechargeable battery
60
Label the components on this BTE hearing aid starting from the top and moving to the right
1. Hook
2. Tubing
3. Earmould
4. Battery component
5. Programme button/ volume control
6 & 7. Microphone port
61
Label the components on this BTE hearing aid starting from the top and moving to the right
1. Hook
2. Battery component
3. Volume control (rocker switch)
4. Programme button (push button)
62
Label the components on this BTE hearing aid starting from the top and moving to the right
1 & 7. Microphone port
2. Hook
3. Battery component
4. Programme button/ volume control
63
Label the components on this BTE hearing aid starting from the top and moving to the right
1. Left/ right indicator (blue for left)
2. Battery component
3. Hook
64
Label the components on these open fit BTE hearing aids starting from the top and moving to the right
Left hearing aid:
1. Microphone port
2. Battery component
3. Thin tube
4. Open fit dome
Right hearing aid:
1. Microphone port
2. Programme button/ volume control
3. Open fit dome
4. Thin tube
65
Label the components on this open fit BTE hearing aid starting from the top and moving to the right
1. Thin tube
2. Open fit dome
3. Battery component
4. Programme button/ volume control
5. Microphone port
66
Label the components on this RIC hearing aid starting from the top and moving to the right
1. Microphone port
2. Thin tube
3. Receiver
4. Battery component
5. Volume control (rocker switch)
6. Programme button (push button)
67
Label the components on this RIC hearing aid starting from the top and moving to the right
1. Thin tube
2. Volume control
3. Programme button
4. Receiver
68
Label the components on this ITE hearing aid starting from the top and moving to the right
1. Programme button (push button)
2. Vent
3. Volume control/ off switch (rotating dial)
4. Battery component
5. Microphone port
69
Label the components on this CIC hearing aid starting from the top and moving to the right
1. Left/ right indicator (red= right ear, blue= left ear)
2. Removal thread
3. Battery component
4. Microphone port
70
What is gain and how do you calculate it?
-The gain is the difference between the input sound level (dB SPL) and the output sound level (dB SPL)
-Gain= Output (dB SPL) - Input (dB SPL)
71
What is the name of this graph? What is it showing?
-Input-output graph
-Shows the output from a hearing aid for a range of inputs
-Slope of the graph is the gain of the hearing aid
72
What is linear amplification?
-When a hearing aid amplifies different levels of input by the same amount
-The gain remains constant whether the input level to the hearing aid is high (loud) or low (quiet)
-There is usually a limit to the output from a hearing aid so the linearity of the air tails off at high input levels
73
What is the frequency response of a hearing aid?
The variation of gain supplied at each frequency depending on the degree of hearing loss at each frequency
74
What is this graph called? What is it showing?
-Frequency response curve
-Green line is the frequency response
-Gain is varying across the frequencies of sound
75
What is known as the maximum output of the hearing aid?
The maximum output is the maximum intensity of sound that the hearing aid can produce
76
What can happen to the sound at maximum output levels?
It may start to become distorted by the hearing aid
77
What is output measured in?
dB SPL
78
What is harmonic distortion?
-The distortion of sound caused by harmonics of the organic sound
-Usually the lower harmonics are the most powerful
79
What is the value that the total harmonic distortion should fall below for the comfort of the hearing aid wearer?
Less than 10%
80
What is intermodulation distortion?
If there are 2 or more frequencies in the input e.g. f1 and f2, distortion products may occur at f1-2, 21-f2, 2f2-f1 etc.
81
What is used to measure the output from a hearing aid?
Test box
82
What are the four components of a test box?
1. Test chamber with tight-fitting lid to prevent interference from background noise
2. Loudspeaker to present the stimulus sound
3. Measurement microphone to measure the output level from the hearing aid at the point it enters the microphone
4. Coupler to connect the hearing aid to the measurement microphone
83
What is non-linear amplification (compression)?
-Change in gain as a result of changes in input intensity level at a given frequency
-Gain different for quiet sounds and loud sounds
84
What are the two factors that cause the gain from a hearing aid to vary?
1. The frequency of the sound
2. The intensity of the input (at each frequency)
85
What is the difference between the frequency response and the input-output function?
-The frequency response shows the variation in gain across the frequencies amplified by the aid
-The input-output function shows the variation in gain across the different input intensities at a SPECIFIED FREQUENCY
86
Why do we need compression?
-The range of sounds that the normal auditory system can cope with is large (e.g. 0-100 dB HL)
-The range of sounds an impaired auditory system can cope with is smaller (i.e. the patient has a reduced dynamic range)
87
What is main problem with linear amplification for people with a reduced dynamic range?
Overamplification- linear hearing aids can amplify to levels above the wearers ULLs causing discomfort which can be severe enough to stop people using hearing aids
88
What is done to solve the problem of overamplification?
Output limiting ~ reduces the dynamic range of incoming signals to within the patient's dynamic range of hearing
89
What are the two ways of output limiting?
1. Peak clipping (PC)
2. Compression (Automatic Gain Control or Automatic Volume Control)
90
Describe how peak clipping works
-Clips the peaks and troughs of the waveform when it comes too loud
-Reduces the loudness of the signal so that it is within the wearer's dynamic range
91
What is the problem with peak clipping?
-It introduces distortion into the waveform and therefore reduces the quality of the sound
-The signal becomes very different from the original
92
Describe compression
-The range of input sound intensities is compressed (squashed) into a smaller range of output intensities
-The "dynamic range" of the output is less than that of the input
-The amplitude of the speech signal is reduced but the integrity and shape of the waveform is retained which prevents distortion
93
What are the two types of compressor characteristics?
1. Dynamic characteristics: determine how quickly the compression operates
2. Static characteristics: determine when compression is active and the extent of its effect on the gain of the hearing aid
94
How does the waveform envelope illustrate compression?
Sound starts at a particular intensity/ amplitude, increases in amplitude after a few cycles, and then decreases again
95
State the two dynamic characteristics of compression
1. Attack/ activation time
2. Release/ recovery time
96
Define attack/ activation time
The time taken for the hearing aid to activate the compression following a change in input or output level
97
Define release/ recovery time
The finite time taken for the hearing aid to deactivate the compression following a change in input or output level
98
What is the difference between fast and slow acting compression?
-Fast acting compression has short attack and release times
-Slow acting compression has longer attack and release times
99
What is the time frame for attack times?
5-50ms
100
What is the time frame for release times?
20-200 ms
101
State the three static characteristics of compression
1. Compression ratio
2. Compression threshold
3. Compression kneepoint
102
What is the compression ratio?
-Change in input level needed to produce 1 dB change in output level
-A high compression ratio gives a small change in output relative to the change in input
-This leads to a wide range of inputs being compressed into a far smaller range of outputs
103
What compression ratio does linear amplification have?
1:1
104
If a 10 dB increase in input causes a 1 dB increase in output of the hearing aid what is the compression ratio of that hearing aid?
10:1
105
What is the compression threshold?
-The preset level above which compression is activated
-Levels below this are usually amplified linearly
106
What is the compression kneepoint?
-The preset level above which the compression ratio changes
-Changes in compression ratio
107
What is the difference between input and output controlled compression?
In input controlled compression the detector is located on the input side (before the volume control) and in output controlled compression the detector is located on the output side (after the volume control)
108
In input-controlled compression, what two characteristics are affected by volume?
Gain and MPO (maximum power output)
109
In output-controlled compression, what two characteristics are affected by volume?
Gain and kneepoint
110
What is the purpose of output limiting compression?
To stop sounds exceeding ULLs and to reduce distortion at high sound levels
111
What is the purpose of wide dynamic range compression (WDRC)?
To make the most of the dynamic range of that person and maintain the loudness relationships in complex sounds
112
What is the purpose of comfort compression?
To make moderate and loud sounds more comfortable
113
What is the purpose of syllabic compression?
To reduce the loudness contrasts between different elements of speech
114
What are the characteristics of output limiting compression? (7)
-Quick acting
-High compression ratio above the kneepoint (e.g. 10:1)
-Acts at high levels of sound
-Output-controlled
-Parameters might be different at different frequencies
-Similar I/O function to peak clipping
-Better at peak clipping as much less distortion
-Important for severe to profound losses but useful for all hearing losses
115
What are the characteristics of wide dynamic range compression? (7)
-Aims to restore loudness reproduction in moderate losses
-Low kneepoint (40 or 50 dB)- acts on moderate and loud sounds
-Low compression ratio, typically <2:1
-Input controlled
-Less distortion and more faithful reproduction of input compared to peak clipping
-Activation times need to be set carefully
-Multiple channels are helpful
116
Describe the differences between compression limiting and WDRC as depicted in this image
-If we apply compression limiting, all of the sound intensities are within the dynamic range so they are comfortable but the loudness relationships are not maintained
-This means that moderately loud and very loud sounds sound the same
-WDRC does maintain loudness relationships between different intensities of sound so different intensities of sound are perceived as different
117
What are the main characteristics of comfort compression? (7)
-Aims to reduce moderate and loud sounds to a comfortable level
-Moderate kneepoint i.e. 60 dB
-Low compression ratio, often around 4:1
-Slow activation times
-Input controlled- volume control still effective
-The overall effect on loudness is somewhere between WDRC and output limiting compression
-Useful for loud sound environments
118
In which patients would you consider compression?
Patients with sensorineural or mixed hearing loss who have a reduced dynamic range (but can still be helpful for patients who do not have a reduced dynamic range)
119
How do activation and deactivation times affect the sound heard by the hearing aid wearer?
-Short times are helpful for maintaining the loudness relationships between different parts of speech e.g. loud vowels vs quiet consonants
-Long times are helpful for maintaining comfort when listening in background noise
120
What is expansion?
-The opposite to compression
-As input level increases, the gain increases
-This means softer sounds are amplified less than loud ones
121
Which patients is expansion useful for?
People with good low frequency hearing and a moderate loss at mid and high frequencies who can hear internal noise from their hearing aid or low level background noise and find it distracting
122
What is digital signal processing?
Signal processing is anything that manipulates the sound signal including amplification, filtering, compression, frequency lowering etc.
123
What are the two main advantages of digital signal processing?
1. Allows better fitting of the audiogram
2. Improves signal to noise ratio
124
What are the two types of WDRC?
1. Base increase at low levels (BILL)- WDRC affecting low frequencies
2. Treble increase at low levels (TILL)- WDRC affecting high frequencies
125
What is BILL used for?
-Aims to provide good listening for speech in background noise
-Used for patients with significant low frequency hearing loss
-Low frequency background noise is compressed more than the higher frequencies so that speech clarity improves
-Has a low kneepoint for the low frequencies, and a higher kneepoint for the high frequencies
126
What is TILL used for?
-Aims to ensure sounds are not overamplified where the wearer has a reduced dynamic range
-Used for patients with a mild to moderate high frequency loss with reduced dynamic range in the high frequencies
-High frequencies compressed more than the lower frequencies so the hearing aid output stays within the wearer's dynamic range
-High kneepoint for the low frequencies, low kneepoint for the high frequencies
127
What are directional microphones used for?
To improve the signal to noise ratio by controlling the shape of the polar plot and automatically switching between directional and omnidirectional modes
128
What is a polar plot?
-A way of mapping the area from which the hearing aid mic collects sound from around the wearer
-E.g. omnidirectional microphones collect sound from all around the wearer, cardiod microphones collect sound from in front of the wearer
129
What are fixed directional microphone systems?
-Polar plot remains the same
-Different polar plots may be stored in different programmes but settings do not change
130
What are automatically activated fixed directional systems?
-Polar plot is fixed but the presence of background noise causes the directional mic setting to change automatically
-Useful for particular programs for particular listening situations
131
What are automatically activated adaptive directional mic systems?
-Turn the directional mic on and off when needed
-Can change the polar plot in response to changes in the listening environment
-Hearing aid can modify the response of the aid in response to changes in noise levels without the user having to make any changes
132
What are frequency specific directional microphones?
-Frequency and location of noise determines the polar plot
-Improves signal to noise ratio for multiple sources of noise
-Fast processing of sound by hearing aid required
133
Which hearing aid feature heavily relies on the presence of feedback cancellation?
Open moulds or open-ear fittings
134
What are the two methods of feedback cancellation?
1. Notch filtering- reduces the gain in a narrow frequency range
2. Phase cancellation- produces a sound in reverse phase to the noise
135
How does notch filtering cancel feedback?
Notch filtering uses filters to reduce the gain at the frequencies at which feedback occurs
136
What are the two types of filters used in notch filtering?
1. Static- set by running a check with the hearing aid programming software which identifies the frequency bands where the feedback is occurring
2. Dynamic- hearing aid continuously monitors the output for feedback and creates a notch filter at the appropriate frequency
137
What is the advantage that active notch filtering has over static?
It is more effective because it changes as the frequency of the feedback changes
138
What is the disadvantage of active notch filtering over static notch filtering?
It can be slow to adapt to changes in noise
139
How does phase cancellation act as a form of feedback cancellation?
1. Aid microphone picks up feedback
2. Processor reverses feedback by 180 degrees
3. Transducer emits reversed signal causing cancellation
-Can remove several feedback tones at the same time without affecting the quality of speech sounds
140
What is the effectiveness of phase cancellation dependent on?
The processing power of the hearing aid and battery life
141
What is noise reduction?
The process of reducing or eliminating the noise without having a significant effect on the speech signal
142
What are the two methods of noise reduction?
1. Spectral subtraction: Frequency spectrum of the noise is estimated and then subtracted from the speech signal
2. Phase cancellation: Exact waveform of the noise is measured and a sound is produced with identical but reverse phase to cancel it
143
Why do people with a precipitous high frequency hearing loss tend to miss high frequency information even when wearing hearing aids?
-A large amount of gain is required at high frequencies causing feedback
-The high frequency hearing loss is caused by a "dead region" within the cochlea
144
What are "dead regions" within the cochlea and why do we avoid amplification in these areas?
-Caused by severe high frequency hearing loss
-Amplification does not benefit hearing in the dead region because the extent of hair cell death is too great
-The high levels of gain applied in the dead region can reduce frequency discrimination for other sounds
145
What is the purpose of frequency lowering?
To move high frequency sounds to a lower frequency in order to improve their audibility
146
What do frequency transposition aids do?
Transpose specific high frequency area down by 1 or 2 octaves and mix it with the sound in the lower frequency area
147
What do frequency compression aids do?
Take high frequency sounds above a certain frequency and apply a frequency compression ratio to them
148
What do frequency translation aids do?
An adaptive algorithm looks for high frequency components likely to be speech, copies the sound and presents it at a lower frequency
149
What are three examples of wireless communication?
1. Ear-to-ear communication- enables signals from both ears to be combined and processed together
2. Remote programming- enables programming and fine tuning of the hearing aid without having to visit the hearing care provider
3. Direct connectivity- can connect directly to phone, TV for better signal to noise ratio
150
What are the physical patient factors affecting hearing aid candidacy?
1. Craniofacial status- is it possible to fit hearing aids based on the structure of the outer and middle ear?
2. Vision- is the patient able to see well enough to operate hearing aids and read supporting materials?
3. Manual dexterity- does the person have enough mobility and sensation in their hands to operate and maintain hearing aids?
4. Other health conditions- do they have other health conditions that may affect the hearing loss or their ability to wear hearing aids?
151
What are the sociological patient factors affecting hearing candidacy?
1. Work environment- do they work in an environment where hearing aid use is possible and what features would be particularly useful?
2. Activities- what hobbies and social activities does the person do? Will hearing aids be an advantage or disadvantage in those situations?
3. Personal support- does the person live with other people or have family and friends who can support them with hearing aids?
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What are the communication patient factors affecting hearing aid candidacy?
-Does the patient identify that the hearing loss is affecting their communication ability?
-Do they use spoken or visual language?
-Are hearing aids to be used for speech perception or awareness of sound?
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What are the audiological patient factors affecting hearing aid candidacy?
1. Type and pathology of hearing loss- hearing aids often appropriate for sensorineural and mixed hearing loss, sometimes for conductive loss
2. Severity of hearing loss- very mild/ profound losses may not benefit from amplification
3. Unilateral/ bilateral loss- if there is a hearing loss in both ears more benefit will be obtained from wearing 2 aids
4. Speech discrimination- measurement of speech discrimination can provide indications of hearing aid benefit and how much to increase the SNR
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What are the psychological patient factors affecting hearing aid candidacy?
1. Cognitive and mental status- working memory, social isolation, does the person feel able to manage hearing aids
2. Motivation- does the person identify the impact of their hearing loss on their listening, communication and activities, are they ready to take action to address their hearing difficulties and disclose their hearing loss?
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What can electroacoustic characteristics of hearing aids be altered by? (6)
1. The prescription fitting rule used
2. Multiple channels and bands
3. Noise reduction features
4. Feedback and occlusion management systems
5. Directional microphone settings
6. Multiple memories
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What is the "fitting range" of the hearing aid?
The fitting range refers to the threshold range that the hearing aid is suitable for depending on the shape and contour of the hearing loss dynamic range
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What are the benefits of bilateral hearing fitting for binaural hearing loss?
-Loudness summation
-Better sound localisation
-Better speech intelligibility
-No auditory deprivation
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Why is the style/ form an important factor in hearing aid fitting?
-Can affect ease of handling i.e. insertion/ removal of hearing aid, ability to change batteries
-Appearance of hearing aid can significantly affect acceptability
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Why do the controls have to be taken into account during hearing aid fitting?
-Is there a need to activate program or volume control?
-Will the wearer be able to use the controls easily?
-Will the controls alter the shape/ size/ style of the hearing aid?
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Why is connectivity an important factor for hearing aid fitting?
-Can help to improve signal to noise ratio and access to the phone, TV and remote mics
-However multiple settings can be confusing for the hearing aid wearer
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Why does cost have to be taken into account during hearing aid fitting?
-Substantial investment for the client or the NHS department
-However individual and societal cost of untreated hearing loss is greater- important for the wearer to use their hearing aid
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What are the two approaches to identifying the correct hearing aid settings for a hearing aid wearer?
1. Prescriptive approach- some characteristics of the hearing-impaired person are measured and the required amplification characteristics are calculated from them
2. Experential/ evaluative approach- number of hearing aids are compared and an attempt would be made to find the best one through patient reports and assessment of hearing aid performance
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Why is the prescriptive approach used over the experiential approach?
-Quicker
-Prescription formulae assumes a relationship between the person's hearing loss and their amplification requirements
-Usually based on audiometric thresholds or Loudness measurements
-Calculates an "ideal" target output for the hearing aid from this information
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What are the two main prescription formulae used for hearing aid fitting in the UK and what are their aims?
1. NAL NL2- aims to maximise speech intelligibility at the listening level preferred by the aid wearer. Intelligibility is assumed to be maximised when all bands of speech are perceived to have the same loudness
2. DSL v5.0- aims to make speech sufficiently audible to allow speech perception without discomfort for all degrees of hearing loss
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What is NAL NL2 based on?
Loudness of speech
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What is DSL v5.0 based on?
Audibility
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What input levels does the NAL-NL2 algorithm calculate target insertion gain for?
Target insertion gain for different input levels (50-, 65 and 80- dB SPL)
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What is "effective audibility"
-NAL-NL2 prescription algorithm looks at "effective audibility" ~ known as how much information can be extracted from sounds once they are audible
-For patients with severe or greater hearing loss, increasing the sensation level will not necessarily add much more information for understanding speech ~ i.e. increase in audibility does not add "effective audibility"
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Which frequencies does NAL-NL2 provide less gain for?
The low frequencies where the speech is more intense
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What input levels does the DSLv5.0 algorithm calculate target output for?
Target output for different input levels (40-, 65- and 95-dB SPL)
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What does the DSL v5.0 focus on?
Amplifying speech to a sufficient sensation level (i.e. comfortable listening level) in order to maximise intelligibility
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What kind of hearing aid fitting was DSL v5.0 originally designed for?
Paediatric fitting
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What is loudness normalisation?
-Restoration of loudness perception to the same loudness perceived by a listener with normal hearing
-Soft, medium and loud speech sounds are amplified appropriately to reflect how they are heard by an individual with normal hearing
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What is loudness equalisation?
-Equalise the perception over a range of frequencies
-Lower frequencies do not dominate loudness
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What are the two things NAL-NL2 prescription aims to do?
1. Make speech intelligible
2. Make loudness comfortable
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What are the main differences between NAL-NL1 and NAL-NL2?
-NAL-NL2 prescribes relatively more gain across low and high frequencies and less gain across mid frequencies than NAL-NL1
-NAL-NL2 takes into account age, gender, language type, binaural/ monoaural fitting, hearing aid experience and compression speed
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How does NAL-NL2 take into account age?
-Children tend to prefer more gain than adults
-NAL-NL2 provides more gain at low input levels for children but less gain at high inputs for adults
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How does NAL-NL2 take into account gender?
-Women prefer an average of 2 dB less gain than men
-Men are prescribed 2 dB higher gain than women
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How does NAL-NL2 take into account the effect of language?
-Sufficient gain is applied at the frequencies that are most important for speech understanding
-Low frequencies are more important in tonal languages so more gain is prescribed for low frequencies in speakers of tonal languages
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How does NAL-NL2 take into account binaural fitting?
-Listening with two ears provides more loudness than listening with one
-Less gain is used for binaural fittings, especially at higher input levels
-Bilateral correction is 2dB across low input levels and 6dB for high input levels
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How does NAL-NL2 take into account hearing aid experience?
-No difference in the gain preferences between new and experienced hearing aid users with a mild hearing loss
-New hearing aid users with a moderate hearing loss prefer significantly less gain than experienced hearing aid users with a moderate hearing loss
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How does NAL-NL2 take into account compression speed?
-Listeners with severe or profound hearing loss prefer lower compression ratios than those prescribed by NAL-NL1 when fitted with fast-acting compression
-NAL-NL2 prescribes lower compression ratios for fittings with fast-acting compression
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How does DSL v5.0 take into account adult/ acquired hearing loss populations compared to paediatric/ congenital?
7 dB reduction for moderate losses and 3 dB for severe losses
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How does DSL v5.0 take into account interpolation?
Greater number of target values across frequencies when working with partial audiograms
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How does DSL v5.0 take into account compression threshold?
Less gain and output for low-level inputs due to prescribed compression threshold (inputs of 70 dB and above are not affected
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How does DSL v5.0 take into account output limiting?
-Narrowband output limiting targets largely unaffected
-Output limiting for speech may cause target reductions of 5-10 dB if hearing loss is severe or test level is high
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How does DSL v5.0 take into account quiet vs noisy environments?
Compression threshold raised by 10 dB and gain reduced at low-importance speech frequencies by about 5 dB
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How does DSL v5.0 take into account binaural fittings?
-Will reduce targets for speech by 3 dB
-Output limiting targets are not affected
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How does DSL v5.0 take into account conductive or mixed hearing loss?
Increases gain by up to 9dB for mild losses, 5dB for severe losses, depending on magnitude of air-bone gap
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What are the 6 key factors on which NAL-NL2 and DSL v5.0 and how do they differ?
1. Gender: NAL-NL2 increases gain by 1 dB for male HA wearers and reduces gain by 1 dB for female wearers. DSL does not adjust
2. Experience: NAL-NL2 incorporates adjustments for experienced HA wearers, DSL does not adjust
3. Correction for air-bone gap: DSL correction adds 5-9 dB of gain, NAL-NL2 prescribes gain for sensorineural component and then adds 75% of the air-bone gap to this value
4. Binaural fittings: DSL targets reduced by 3dB, NAL-NL2 reduces by 2dB at low input levels and 6 dB at high levels
5. Loudness discomfort: DSL alters prescription of gain, NAL0NL2 does not alter gain based on ULLs
6. Listening in noise: DSL targets reduced by 3-5 dB for low-importance frequencies in noise, NAL-NL2 does not correct for noise
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How do clinical outcomes differ between DSL and NAL in children?
-Speech perception good for both
-SRTs and consonant scores similar to normal hearing children
-Parents' and teachers' observations revealed no effect of prescription
-Children prefered NAL-NL1 in real world noisy situations
-More negative comments about noise for DSL
-More positive comments about loudness comfort for NAL
-For optimum audibility of soft speech children need more gain than is prescribed by NAL-NL1
-To achieve listening comfort in noisy places, children need less gain than DSL
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Name the two fitting strategies
1. Device independent fitting strategy
2. Proprietary fitting strategy
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Describe the device independent fitting strategies
-E.g. NAL, DSL
-Prescription formula not hearing aid dependent
-Published by non commercial research groups
-Stronger evidence base
-Information in public domain
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Describe the proprietary fitting strategies
-Found in individual manufacturers' fitting software
-Related to particular circuitry/ technology
-All hearing aid manufacturers have their own proprietary fitting rules
-Information protected (not public)
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When a hearing aid user turns 18 what prescription formula should they be on?
Keep them on DSL unless they are having problems hearing
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What is the name for this graph and what is it showing?
-SPL-ogram
-Shows hearing thresholds, prescription targets, ULLs or predicted maximum output, unamplified sound levels and amplified sound levels
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Describe what each line on the SPL-ogram is showing
1. Blue line is showing ULLs (either predicted or measured, OR maximum output levels)
2. Green line is showing hearing aid output targets which are created by the fitting prescription
3. Hearing thresholds for the patient
4. Hearing thresholds for normally hearing people (e.g. 0 dB HL on an audiogram)
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What does 0 dB HL mean on the SPL-ogram?
It is the average hearing threshold for young adults
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What kind of compression would this patient need and why?
-Sensorineural hearing loss
-Need output limiting compression to prevent sounds from exceeding the patient’s ULLs and to prevent distortion
-WDRC used to maintain differences in loudness- quiet sounds sound quiet, moderate sounds sound moderate and loud sounds are loud
-WDRC is only useful when we have an adequate dynamic range left, which we do in this case
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What kind of compression would this patient need and why?
-Mild to moderate sensorineural hearing loss which is worse in the higher frequencies
-Slightly sloping
-ULLs expected at the level of a normally hearing person’s
-Reduced dynamic range across all frequencies
-Compression needed across all frequencies
-WDRC can be used- still a reasonable amount of dynamic range to fit quiet, moderate and loud sounds in
-Output limiting to reduce distortion and to prevent exceeding ULLs
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What kind of compression would this patient need and why?
-Moderate conductive hearing loss which is worse at the low frequencies (gentle reverse slope)
-Output limiting compression needed to prevent distortion of loud sounds (receiver and microphone vibrating a lot to cause distortion) but not to prevent exceeding of ULLs- conductive loss does not involve reduced dynamic range
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What kind of compression would this patient need and why?
-Moderate to severe sensorineural hearing loss worse in the high frequencies
-Dynamic range likely to be reduced
-Need output limiting compression
-Could do WDRC at the lower frequencies but at the high frequencies the dynamic range might be too small to be successful
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In which situations would you use directional microphone settings?
-Listening in noisy environments- can change the polar plot to focus on the person you are talking to
-Car setting: microphones focus on the left or behind to allow you to listen to other people in the car
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In which situations would you use a noise reduction program?
-In noisy environments
-Nowadays combined with directional microphones
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In which situations would you use feedback cancellation?
When you have feedback and you are unable to get a good fitting earmould for some reason
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When would you use wireless connectivity?
Collection of sound from both microphones and process as one entity leads to improvement in noise reduction and directional microphone algorithms
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When would you use frequency lowering?
With sloping high frequency hearing loss
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What is data logging and data learning?
-Data logging collects information on how the hearing aid is being used (how long, which programs, how much the volume is being increased/ decreased)
-Data learning is when the software learns about your hearing aid usage and makes adjustments automatically
-Very useful for certain people who you cannot see every day but may need extra help with their hearing aids
