Audiology 6- Hearing aids Flashcards
1
Q
what is gain in a hearing aid?
A
-gain is amplification
- the difference between the output and input of the hearing aid
- typical maximum gain for low powered hearing aid is 50dB
- for high powered aids the maximum gain is approx. 75dB
2
Q
what is maximum output of a heairing aid?
A
- as loud as the amplifier will go
- also known as saturation sound pressure level (SSPL)
- typically the SSPL for low powered hearing aids (mild/moderate loss) is 120 dBSPL or less
- for high powered aid (severe/ prodound loss) the SSPL is 135dBSPL
- does not exceed the uncomfortable loudness level of the wearer
3
Q
what is frequency response of a hearing aid?
A
- range of frequencies over which the amplifier amplifies
- most aids amplify over a range of about 200Hz to 4000Hz +
- Difficult to push anything above 4000 Hz through the tube of a behind the ear hearing aid
4
Q
what is distortion of a hearing aid?
A
- how much does it distort the output signal as compared to the input signal
5
Q
What is a behind the ear/ power aid (receiver- in- the- aid) ?
A
- has a microphone, battery, processor, receiver all housed within hearing aid case, shaped to fit behind the pinna
- output through tube via conventional earmold or open fitting
6
Q
what are the two types of hearing aid styles
A
- in the ear
- behind the ear
7
Q
What is a behind the ear with convention earmold hearing aid?
A
- have a fitted earmold which almost completely fills the outer ear and ear canal
- separates sound output from the microphone and so reduces feedback
- may be easier to handle as they’re bigger
8
Q
What are the benefits of a behind the ear open fit hearing aid?
A
- open fitting has a number of benefits:
comfort
reduction of occlusion effect
uses normal ear resonance
cosmetic benefits (smaller and can’t been seen) - but cannot be used for severe or profound loss as they aren’t powerful enough
9
Q
What is a receiver- in - the canal hearing aid and what are the benefits?
A
- similar to open fit aids but receiver is at the end of a wire and situated in the ear canal
benefits over a receiver in the aid fitting
- receiver in the canal means it is smaller
- can be used for mild to severe loss
- offers more gain in high frequencies
- smoother frequency response in the mid-high frequencies
- reduction of occlusion effect
10
Q
what are in the canal, completely in the canal and invisible in the canal hearing aids?
A
- their components are all housed in a case which is custom made to the individuals’ ear
- suitable for mild to moderate/ severe losses
11
Q
what is a compression hearing aid?
A
- amplitude compression
- high gain for low intensity sounds
- low gain for high intensity sounds
- gain must vary depending on the input signal
- a compression aid turns down its gain as the input to the aid increases
12
Q
what is signal processing
A
- number of different strategies to:
- makes the hearing aid more comfortable for the users
- offers more benefit in terms of speech perception for the user
13
Q
what is a frequency compression hearing aid?
A
- circuit that compresses the higher frequencies down to the lower frequencies where the user’s hearing is better
- improves speech perception in adults and children but alters the pitch of sound
14
Q
what is a multi-channel hearing aid?
A
- you can divide the amplification strategy across different frequency bands so different amounts of gain and different compression strategies can be applied across these bands
- some hearing aids have 20 channels or more
- means a hearing aid can be tuned to match an individuals audiogram configuration
- beneficial for people with moderately or steeply sloping hearing loss
- can lead to improved speech perception and sound quality
15
Q
what is a multi-programme aid?
A
- two or more different processing set-ups which can be saved to an individual aid and allows the patient to switch between them depending on the listening situation
- e.g. second program may be implemented for noisy situations or music
16
Q
what is a noise reduction/ cancellation aid?
A
- attempts to sperate speech signals from noise signals and process the two types of signals differently
- attempts to detect the presence of speech and turn down the gain if no speech or minimal speech is present
- a speech non-speech detector analyses fluctuation in signal amplitude
- if the speech/ noise signal envelope is characteristic of speech, the hearing aid is programmed to amplify that channel
- if the speech/ noise envelope is characteristic of noise, the signal is assumed to be noise and amplification in the channel reduced
- works better for speech in background noise that is not speech noise e.g. traffic
17
Q
what is a directional/ multi- microphone hearing aid?
A
- most effective method of improving the signal- noise ratio
- directional microphones that enhance the hearing aids sensitivity to sounds from a desired direction, over other directions
- only technology that can effectively pick out desired speech signal in undesired background speech
- can be fixed or adaptive
- uses dual/ multi-microphones the hearing aid can be set to amplify sounds from one direction
- works on time of arrival of sound. sounds that reach the front mic first are amplified, those that reach the rear mic are not
18
Q
what is acoustic feedback?
A
- caused by amplified sound leaking from the ear canal back to the microphone
- occurs when earmould is poor acoustic fit
- occurs when an ear canal is occluded or partially occluded by wax
19
Q
what are the aims of amplification?
A
- to increase the intensity (amplify) and customise frequency response to compensate for hearing loss across frequencies, providing:
- signal detection
- signal localisation
- speech discrimination in quiet
- speech discrimination in noise
(bottom of the list are harder to achieve) - prevent sounds becoming too loud
- increase clarity
- comfort
- socially acceptable for patient
20
Q
limitations of hearing aids
A
Today’s hearing aids cannot:
- completely restore normal hearing thresholds
- restore the sophisticated frequency resolution of the normal cochlea
- eradicate acoustic feedback
-eradicate background noise whilst preserving speech
21
Q
realistic expectations of hearing aids
A
- the variety of signal processing strategies help to restore the audibility of low-level sounds and deliver them at a comfortable volume in each frequency band/ channel
- sophisticated noise reduction and directional microphone technologies are making hearing aids more comfortable to use and increasingly allow people with hearing loss to cope with noisy/ difficult listening conditions
- benefit is greatest for mild-moderate/ moderate losses
22
Q
what is signal to noise ratio?
A
a comparison that is useful for estimating how understandable speech is in a room
the sound level of the teacher’s voice in dB, minus the background noise level in the room in dB= the S/N in dB
a large S/N means better speech perception
23
Q
what is the recommended signal to noise ratio in a classroom
A
+15 dB
for some children with hearing impairments it needs to be +20dB
24
Q
where is the lowest signal to noise ratio in the classroom?
A
either:
- at the back of the classroom, where the teacher’s voice has fallen to its minimum value
- near the noise source, where the noise is at its maximum
25
what is a sound- field amplification system
- works by sending an FM or infrared signal from the teacher's transmitter to an amplifier which is connected to one or more loudspeakers in the classroom so all students benefit
- rooms require reasonably good sound insulation to prevent amplified sound transmission to adjacent rooms as well as low reverberation
26
what is a bone conduction aid?
- transmission is direct to the cochlea
- candidacy: suitable for conductive/ mixed losses
27
what is a bone anchored hearing aid?
non- implanted
difficult to wear, poor cosmetically and uncomfortable
suitable for: conductive/ mixed losses and people who cannot wear a conventional air conduction hearing aid
28
what are the advantages of bone anchored hearing aids
- works without pressure
- secure and always in the right
- discrete and more cosmetically acceptable
- improved and stable sound quality
- no occlusion of the ear canal
- no feedback
- allows ear infections to be treated and permits air flow to the ear canal
29
what are the disadvantages of bone anchored hearing aids?
- invasive
30
what is a cochlea implant
- a device that can help improve the hearing abilities of people who are severely or profoundly dead by electrically stimulating the auditory nerve
31
who is a cochlea implant suitable for?
- suitable for those who cannot gain any useful benefit from hearing aids and who rely instead on speech- reading to understand speech
- for those who have had hearing so remember sound and to young children who have been born deaf
32
what is the adult criteria for a cochlea implant?
- severe/ profound bilateral sensori-neural deafness > 70dBHL
- speech audiometry score < 50%
- limited benefit from conventional amplification
- radiologically appropriate
- health state commensurate with surgery
- appropriately motivated
- social support from family and friends
33
what is the paediatric criteria for a cochlea implant?
- profound bilateral sensori-neural deafness > 90dBHL
- age 10 months - 17 years
- limited benefit from conventional amplification > 55 dBHL
- preference for aural communication programme
- radiologically appropriate
- health state commensurate with surgery
- appropriate expectation and family commitment
34
how does a cochlear implant work?
- the signal processor is responsible for breaking the input into different frequency bands/ channels and delivering the filtered signals to the appropriate electrodes in the array
- in multi-channel cochlear implants, different parts of the electrode are stimulated depending on the frequency of the sound signal and exploit the place mechanism for coding frequencies
- the base of the cochlea is stimulated with high frequency signals, while the apex is stimulated by low frequency signals
- electrodes stimulate the auditory neurons directly, bypassing the hair cells
35
what are the cochlea implant performance expectations?
- cochlear implants do not restore normal hearing, but can significantly improve audibility and speech recognition for severely and profoundly deaf adults and children, even without speech-reading, particularly in good listening conditions
