Hearing Aids 2 Flashcards
(24 cards)
What are the aims of amplification for a hearing aid?
- To increase the intensity and customise frequency response to compensate for an individual’s hearing loss across frequencies.
- Detect there are sounds around or they know someone is speaking.
- Localise the sound so the person knows where it’s coming from (sound localisation).
- Speech discrimination in quiet environments.
- Speech discrimination in noise which is quite challenging for the hearing aid to do effectively.
- Prevent sounds becoming too loud so we don’t want loud sounds to be amplified.
- Increase clarity which can be achieved by frequency compression but it can’t replicate the fine tuning of the higher frequencies the OHCs do in the cochlear along the basilar membrane.
- Be comfortable.
- Be socially acceptable and cosmetically appealing.
What are the realistic expectations a hearing aid can do?
- Compensating for decreased audibility, especially in high frequencies so it can amplify specific sounds depending on the individual’s audiogram and specific hearing needs.
- Compensating for loudness recruitment where the person is experiencing a reduced dynamic range of hearing so the hearing aid can amplify the necessary sounds so they can hear them e.g. using compression.
- Compensating for the decreased speech perception in noise or if background noise and the main target sound are both speech e.g. directional microphones and noise suppression.
What is the main limitation of a hearing aid?
- One thing hearing aids can’t do is increase the frequency resolution in cases of sensori-neural hearing losses because a hearing aid cannot replicate the function of the OHCs fine tuning so making sounds very sharp and clear. Therefore, people with sensori-neural hearing losses experience muffled sounds which the hearing aid cannot directly help combat.
- Also, directional microphones help improve speech perception in noise but the hearing aid does struggle to do this independently.
What are the other limitations of hearing aids?
Hearing aids cannot:
1. completely restore normal hearing thresholds.
2. overcome the clarity problems associated with hair cell loss so they cannot restore the sophisticated frequency resolution of a typically working cochlea.
3. eradicate acoustic feedback (whistling) completely.
4. eradicate background noise whilst preserving speech completely.
What are other realistic expectations of hearing aids?
- The variety of signal processing strategies help to restore the audibility of low-level sounds and deliver them at comfortable volumes across frequency bands/channels.
- Noise suppression and directional microphone technologies are making hearing aids more comfortable and effective to use in noisy/difficult listening conditions.
- Individuals with mild-moderate/moderate hearing losses benefit the most from hearing aids.
What is signal to noise ratio?
This is the teacher’s speaking level in decibels minus the background noise in decibels.
What does a large sound to noise ratio mean?
It means better speech perception and a higher percentage of words understood in the classroom for children.
What is the recommendation for the signal to noise ratio at every point in the classroom?
At least 15dB for children with typical hearing.
+20d for children with a hearing impairment.
This means the teachers voice should be at least +15dB higher than the background noise wherever a child is sat in the classroom. This is hard to achieve without amplification.
What are the two main amplification systems used in classrooms?
- Sound-field amplification systems.
- Radio aids.
What is a sound-field amplification system?
This is where the teacher wears a microphone and the microphone sends a signal to loudspeakers that are scattered around the classroom. This enables the teacher voice to be just as loud throughout the whole room.
This works very well however, the room has to be appropriately equipped e.g. not reverberant (too echoey) otherwise sounds will persist in the room and the room needs good sound insulation to prevent the amplified sounds travelling to adjacent rooms.
What is a radio aid?
The teacher’s voice is delivered from their radio aid directly to the child’s hearing aid.
The child will hear the teacher very clearly, regardless of proximity between the child and teacher because the voice can be carried over distance.
The speaker where’s the wireless transmitter which receives input from the microphone but the transmitter can also be connected to the TV or a computer if the child is watching a video for example.
What are the benefits of using a sound-field amplification system and radio aids?
- A sound-field system within the classroom is inexpensive and benefits all students.
- Amplification systems in the classroom can reduce the need for teacher’s to raise the volume of their voice, so it limits the potential for voice problems.
- Radio aids are typically given to students with a moderate-severe hearing loss.
What are the two implantable devices called?
- Bone anchored hearing aids (BAHAs).
- Cochlear implants.
What is the candidature for people who wear BAHAs?
- Suitable for conductive/mixed hearing losses.
- Suitable for people who experience chronic middle ear infections/pathologies, congenital malformation or damage to their pinna, atresia (narrow ear canals) or who have a chronic ear mould allergy.
What are the components of a BAHA?
The titanium screw is inserted into the temporal bone and there is an abutment attached to the titanium screw and then a processor which clips onto the abutment.
How does the BAHA system work?
The microphone picks up the sound and soundwaves are sent straight to the cochlear, bypassing the outer and middle ear completely.
The BAHA on one side will also send the soundwaves to the contralateral cochlea so both cochlea’s are activated.
What BAHAs are provided for paediatrics?
For very young children, a BAHA Softband is used to allow them to wear a BAHA without the need for surgery.
An implanted BAHA provides better amplification than a softband, especially in the higher frequencies but they still work well as a temporary measure.
What is a cochlear implant?
A cochlear implant is a device that converts the soundwaves into an electrical representation that bypasses the ear and stimulates the auditory nerve.
What is the adult candidature for a cochlear implant?
- Severe/profound bilateral sensori-neural deafness by at least 70dB across 500-4,000Hz frequencies.
- Speech audiometry score of less than 50% correct.
- Limited benefit from conventional amplification/hearing aids.
- Appropriate level of health to cope with surgery.
- Radiologically appropriate (check for risk of ossification where a bone is growing inside someone’s cochlear, meaning the insertion of the electrode array will be unsuccessful).
- Have realistic expectations and a good support network surrounding them.
What is the paediatric candidature for a cochlear implant?
- Profound bilateral sensori-neural deafness of at least 90dB across 500-4,000Hz frequencies.
- Limited benefit from conventional amplification.
- Preference for aural communication programme.
- Radiologically appropriate.
- Appropriate level of health to cope with surgery.
- Realistic expectations and good support network/family commitment.
How does a cochlear implant work?
- The microphones pick up soundwaves.
- The soundwaves are converted into digital information via the sound processor.
- The magnetic headpiece sends the digital signals to the implant.
- The implant directs the digital signals to the electrode array which then sends a signal to the auditory nerve.
- The auditory nerve sends impulses to the brain via the neurons, where the impulses are interpreted as sound.
How many frequency channels will a modern cochlear implant have?
22 frequency channels. The processor divides the incoming sounds into the 22 frequency bands, depending on their specific frequencies e.g. high/low.
What is the role of the electrode array?
- The electrode array is inserted into the scala tympani via the round window and should be hugging the internal wall of the cochlear to be as close to the auditory neurons it will be stimulating as possible.
- Different parts of the electrode array are stimulated depending on the frequency of the sound signal.
- The base of the cochlear is stimulated with high frequency sounds whilst the apex is stimulated with low frequency sounds (like in a normally functioning cochlear).
- The electrodes stimulate the auditory neurons directly, bypassing the hair cells.
What are the limitations of the cochlear implant?
- They do not restore normal hearing thresholds.
- The sound quality can be different to what individuals were hearing beforehand e.g. speech perception in high background noise environments.
- The individual needs to have realistic expectations of their cochlear implant.
