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Hearing Aids > Semester 1 Hearing Aids > Flashcards

Semester 1 Hearing Aids Flashcards

Signal Processing Coupling Ear Impressions Communication Training Hearing Aid Types

1
Q

List the order of a digital hearing aid electronic circuit

A

Analogue input, Microphone, AD Converter, Digitial Signal Processor, DA Converter, Receiver, Output

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2
Q

What does ANR stand for?

What does it involve?

A

Adaptive Noise Reduction
1. Predict Speech Vs Noise
(uses Voice Activity Detector (VAD) to discriminate between speech and noise)
2. Estimate Speech and Noise Levels
Modulates depth signal - diff between max and speech signal and min noise
Useful for a dominant speaker scenario
3. Gain Reduction Algorithms
Splits analogue into all frequencies, if lots of BGN reduces down, however also reduces speech down
4. Gain Reduction Over Time
Dependent on time taken to apply noise reduction
Slow acting: Good for changes in listening environments
Fast acting: Can distort speech, good to reduce noise between syllables/words

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3
Q

Describe a Tele-coil

A

Coil of wire wrapped around a ferrite rod. Picks up magnetic field in the environment (produced by loudspeaker or induction loop) as it has an electrical current with the same waveform.

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4
Q

Describe features of a Directional microphone

A

Consists of two microphones, front as preference to the back.
There is a delay btw front and back, this allows for desired directional preference to be programmed.
Can be adaptive or fixed.

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5
Q

How does a directional microphone work?

A

Receives SPW from analogue signal (in dB SPL). Signal requires amplification to then be processed at DSP, hence preamplifier boosts signal up.
The diaphragm - works similarly to TM

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6
Q

What are thetwo types of microphones

A

Electret Microphone
and
Micro-Electronic-Mechanical Systems (MEMS)

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7
Q

What is an advantage of applying the ICF framework to audiological services?
The ICF is specific to ear-related disorders.
The ICF places emphasis on the impact of hearing loss on a person’s body function and structure.
The ICF accounts for the impact of hearing loss on a person’s day-to-day life.
e. Both (b) and (d) are correct
d. The ICF provides a common language amongst different health professionals.

A

e. Both (b) and (d) are correct

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8
Q

How could audiologists ensure their intervention is meeting the needs of their adult patients?

a. Have a deep understanding of a patients’ hearing loss and audiometric data and use this as the central driver of intervention recommendations.    b. Involve the patient in goal setting and decision-making processes.    c. Recommend a hearing aid based on the audiogram.    a. Decide on patient goals based on the case history, with no consultation with patient.
A

b. Involve the patient in goal setting and decision-making processes.

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9
Q

What is an example of a participation restriction associated with hearing loss in adults?

a. Withdrawal from friendship group
b. Negative attitude from patient’s family doctor
c. Reduced finger dexterity
d. Moderately bothersome tinnitus
e. Reduced speech discrimination in noise

A

a. Withdrawal from friendship group

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10
Q

Your client brings his RIC hearing aid to you and tells you he can hear the startup jingle but it’s not amplifying any sounds. What is the most likely issue?

a. Microphones blocked.
b. Receiver broken.
c. Incorrect battery insertion.
d. Wax filter blocked.
e. All of the above

A

a. Microphone is blocked

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11
Q

Your client arrives for their ear impression appointment. You perform otoscopy and notice a perforation and some discharge in their right ear. What do you do?
a. Call your colleague in to take a look.
b. Proceed with the appointment and obtain an impression.
e. Perform audiometry.
c. Review in 3 months.
Correct!
d. Advise the client to visit his/her GP for further investigation.

A

d. Advise the client to visit his/her GP for further investigation.

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12
Q

Your client comes back from the GP and has received the all clear to be fitted with hearing aids. He tells you that the discharge and perforation persist. They have a flat moderate conductive hearing loss. What mould do you fit?

a. (c) and (d) are both valid options.
b. A full-shell hard acrylic mould with a 1mm vent.
c. A full-shell silicone mould with no vents. You want as much occlusion as possible to avoid feedback
d. A skeleton mould with an open (>3mm) vent.
e. You don’t. It’s best to send him back to the GP for a second opinion.

A

d. A skeleton mould with an open (>3mm) vent.

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13
Q

In hearing aid processing, what dictates the dynamic range and resolution of the digitized signal?
a. The sampling rate of the analogue to digital converter
b. The speed of the digital signal processor used
c. The receiver’s bandwidth
Correct!
d. Number of bits used to represent the analogue signal
e. This is only relevant to analogue hearing aids

A

d. Number of bits used to represent the analogue signal

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14
Q

Why do we employ the Fast Fourier Transform algorithm in hearing aid processing?
a To ensure feedback doesn’t occur
b. To optimise the performance of the adaptive directional microphones
c. To break up a complex signal into its constituent components for further processing
e. All of the above
d. To ensure aliasing doesn’t occur

A

c. To break up a complex signal into its constituent components for further processing

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15
Q

Define dynamic range -

A

The range between the absolute threshold and the maximum loudness threshold.

Average dynamic range is 90 dB.

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16
Q

Why use the WHO Framework?

A
  • Common language across professions and policy makers for describing function
  • Person centred management plans
  • Focus on function and diability in the context of the individual and their lives
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17
Q

Foundations of the ICF…

A

Across the lifespan, a person not the disability, cultural applicability, operational, integrative of both social and medical, person and context, not linear

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18
Q

List the 5 domains of the ICF

A

Body and Structure – Anatomical parts of the body and physiological functions of the body system, including psychological

Activity – Execution of a task or action. The activity limitations e.g. inability to run

Participation – Involvement in a life situation. The limitations of participation e.g. unable to participate in fun run groups

Environmental Factors – Individual (home, work, school). Services and systems (work environment, health care systems, laws, informal rules)

Personal Factors – e.g. gender, race, other health conditions, motivation, lifestyle, education

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19
Q

How would a person with a HL fit into the ICF Framework?

A

Body and Structure: Deficits to the body or physiological function, in this case, the Hearing Loss - SNHL or CHL
Activity: Limitations of the person’s execution of that function i.e. hearing people speaking to them
Participation: Impact on a life situation creating a barrier or restriction to the ability to participate in an activity such as going to the cricket club weekly pub nights.
Environmental factors: Impacts of surrounding environments on the person in terms of infrastructure, awareness and inclusion. The pub is very reverberant, people are often not very accommodating in helping a person to hear by repeating or facing the speaker - unaware, relies on family member i.e. wife to repeat for him
Personal factors: Impacts of other personal factors relating to their individual perception of the impairment or knowledge or attitude towards the impairment. Such as education and understanding of the problem the person is facing in terms of their hearing.

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20
Q

What is the purpose of adaptive noise reduction?

A

To improve speech intelligibility by removing noise.

However, directional microphones are more effective at reducing SNR, than ANR (because ANR focuses on making noisy environments comfortable for the listener)

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21
Q

Describe the Digital Hearing Circuit

A

Analogue signal (speech) enters microphone > microphone converts analogue SPW signal to an electric signal via the diaphragm vibrating, isolater and back plate creating the change in the voltage to transmit > pre-amplifier boosts signal for it to be large enough voltage to be handles at the DSP > AD Converter, converting from analogue to Bits to determine resolution and DR > DSP (ANR strategies) > DA Converter

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22
Q

What are the four ANR strategies:

A
  1. Predict speech vs noise
  2. Estimate speech and noise levels at a certain frequency
  3. Gain reduction algorithms
  4. Gain reduction over time
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23
Q

How does the ANR predict speech vs noise?

A

Uses Voice Activity Detector (within it which determines identification of speech envelope vs noise which is random including whether it’s high pitch or lower pitch noise vs speech peaks)

24
Q

How does the ANR modulate the estimate of speech and noise levels?

A

Calculates the levels of the noise - i.e. ~55dB (averaged across several seconds) to determine long term SNR to reduce the noise?
i.e. good in the car situation

25
Q

Gain reduction algorithms as part of DSP

A

Assesses the signal into specific frequency bands.
Problem is it drops everything down in that freq band - sometimes loses some speech.
Estimates speech

26
Q

Gain reduction over time as part of DSP

A

Dependent on time taken to apply the noise reduction

  • fast acting (reduction of noise btw words, distorts speech)
  • slow acting (good for changes in listening environments)
27
Q

Feedback

A

Increases when gain applied or volume increased manually
Less occluding/larger vent/not fitting properly increased
Bounced by wax
i.e. hugging or cupping hands

28
Q

Why are feedback cancellers good?

A

They send the inverse amount of signal back out to counteract the noise signal and this can provide up to 15dB more gain.
Increasing speech intelligibility

29
Q

List some advantages and disadvatages of DSP

A

Advantages:

  • Easy to adjust signal-processing parameters over a wide range of values via the fitting software
  • Can perform signal processing that is not possible with analogue circuits

Limitations:

  • Some digital signal processing techniques can result in the generation of harmonics, distortion and noise.
  • Each of the signal processing modules requires a certain number of MIPS to run. Limits on processing power affects which algorithms can run simultaneously (i.e. it is small ~5-10MHz and only have about 16kB of memory)
30
Q

What is the highest frequency that can be generated by the DA Converter?

A

Approximately HALF the sampling rate (rather than double, like in AD converter)

31
Q

Whta is the role of the receiver?

A 
To convert the amplified and modified signal back to an acoustic analogue signal.
- Signal/current from DAC reaches coil (magnet) in receiver. The current alternates btw positive and negative current according to the phase of the electrical signal (acting liek a battery but changing its phase). 
Coil gets repelled and attracted as phase is changing.
Coil is also attached to a cone/diaphragm which moves back and forth converting electric signal back into sound waves (pushing air as electrical signal is being processed)
Battery driven (50-90% goes towards moving this coil)
32
Q

Describe the ear impression process:

A

1/. Otoscopy

  1. Oto-Block Placement (size of tip, depth - past the second bend of ear canal, CIC ~5mm past 2nd bend, IIC ~8-12mm past 2nd bend)
  2. Mixing and syringing ear canal material (1:1 ratio, low to high viscosity
  3. Syringing the material (Don’t pull pinna, do not allow syringe to lead material - - Fill the ear canal and as material passes the end of the tip, fill concha bowl, then move into the antihelix, then follow the contour of the ear, finishing at the centre of the concha)
  4. Removing the impression (approx 5minutes horizontal line for custom HAs. Pull pinna up and back to break the seal, gently rotate forward and out)
  5. Otoscopy
33
Q

Why would we use a modified ear impression technique?

A

Lots of elderly clients with have softer/moveable? cartilage… similar to why they have collapsed canals… which could change the shape (not a true reflection of their ear canal). Client reporting a lot of feedback, significant ear canal movement.

As, may cause:

  • feedback
  • loss of retention
  • discomfort
34
Q

What are the modified ear impression technique

A

“Closed-jaw” technique typically used

“Open-jaw” technique: using a bite-block. While doing ear impression, opens ear canal making it a little bigger and fills the ear canal more for less chance of having acoustic feedback.

35
Q

What is the incidence of hearing loss?

A

~5% of the worldwide population have a disabling HL
In Aus, ~14% of the population have a hearing impairment
- MAles affected more than females
- HL kicks in ~61-70yo

36
Q

What defines a chronic hearing loss?

A

Permanent
Caused by no reversible pathological alteration
Leaves residua disability
Requires special training for rehabilitation
Or may be expected to require a long period of supervision and care

37
Q

Factors influencing success of HAs

A
  • Self motivation
  • Patient’s attitude (more positive)
  • Hearing sensitivity and duration of loss (sooner the better, poorer thresholds increase help-seeking)
38
Q

Describe the Health Belief Model

A
  • Psychological modelfocusing on the client’s beliefs and attitudes to predict their health behaviou
    Assumption that action will be taken if: negative health condition can be avoided, positive expectation, believes capabale of performing the recommendation
  • Success factors (self motivation, duration and severeity of loss, patient attitude)
Help seeking generally occurred if:
 Perceived HL as problematic
 Perceive more benefots than barriers
 External prompts (family, environmental difficulty)
 Susceptible to HL
 High self-efficacy
39
Q

Describe the Transtheoretical Model of Behaviour Change

A 
- To help Hearing care professionals relate to client's hearing care journey.
Pre-contemplation
Contemplation
Preparation 
Action
Maintenance
Permanent Exit
Relapse
Involving them in the process/Shared decision making
40
Q

Patient centred care:

A

Holistic, Respond to patient’s emotional concerns, Power balance, Patient as a person, ICF,

41
Q

What is speech reading?

A

n auditory-visual oral language communication skill - linguistic info gathered by watching.
Integration of this visual information to auditory cues

42
Q

What is the MHLT eligibility criteria for HSP?

A

Minimal Hearing Level Threshold?
Eitehr:
- 3 frequency average HL >23dBHL (at 0.5, 1, 2kHz)
- High frequency HL in both ears of > or equal to 40dBHL (12, 3, 4kHz)
- Tinnitus (only allowed to trial the HA)

> If client doesn’t meet HL criteria of >23dB required to complete additional form to determine motivation etc.

43
Q

What are the most common problems with telephone use for somebody who wears HAs?

A
  • Inaudible ringtone
  • Feedback
  • Telecoil interference
  • Difficulty hearing the person on the other end of the phone
44
Q

Troubleshooting for telephone use?

A

Feedback: Foam cover to create acoustic insulation, telecoil program, acoustic telephone program, positioning of the receiver of the phone, feedback manager adjustments, use speaker phone,

45
Q

What is a prescription?

A

a treatment based on a known quantity in order to be most effective. - systematic process of applying factors related to people’s hearing.

Based on:

- hearing threshold, 
- measures of loudness preference
 - loudness discomfort 
 - type of hearing loss etc.
46
Q

Gain amount rules?

A

1/2 rule: Gain should be applied to 1/2 the HL

1/3 rule:Gain should be applied to 1/3 the HL

47
Q

What are hearing aid prescriptions based on?

A 
Optimise audibility (gain/amplification)
Loudness normalisation (restore loudness perception - looking at specific bandwidths as low perceived as louder)
Loudness equalisation ( boost certain parts and not others -for speech)
Speech intelligibility
Listening comfort
48
Q

What does NAL-1 not do?

A

Attempt to achieve loudness normalisation

wanting to maximise speech intelligibility by keeping overall loudness equal
- reduce clients adjust volume and therefore turning all loudness down across freqs.

49
Q

What is the speech intelligibility index? And what are the factors**

A

NAL-1 is based on this index.
Used to predict how much speech is audible to a listener
sum of :
the number of freqs used,
importance of the freq of speech to a listener
number of speech cues are given in a given freq band
distortion factor in a freq band

50
Q

Considerations of SII in NAL-1?

A

Accounts for degree of HL, as speech intelligibility degrades as HL increases, regardless of amplification (distortion)
THEREFORE, NAL1 adjusts its gain and freqg response depending on the input IF the amplification to that region might reduce intelligibility
- cut off point ~73dB

51
Q

NAL-1 gain for CHL?

A

gain is 75% of the Conductive hearing part of the loss (ABG)

52
Q

What were some considerations lacking in NAL-1? LImitations

A

Hearing loss component of Loudness model used.

  • Doesn’t account for tonal languages (low freqs more important for speech intell)
  • Age preference to high gain
  • Gender f prefer less than m
  • Acclimatisation
53
Q

What are the limitations of NAL-2?

A

Loudness discomfort levels nor considered
Hl with a conductive overlay
Cochlear dead regions (IHCs therefore less gain at these regions due to distortion)

54
Q

How do we measure hearing aid output in the ear?

A
  • Placing a thin silicone probe tube close to the ear drum and attached to a microphone
  • to measure (pinna an EE resonances, HA amplification - in the ear, mould effects - venting mould etc)
55
Q

Test box procedure

A
  1. Hearing aid is connected to the 2cc coupler (connected via appropriate adapter i.e. HA‐1 or HA‐2)
    HA1 one component HA2 two components
    2. Positioned in the test box with reference mic positioned 5mm from hearing aid microphone
    3. Lid of test box is shut and test stimulus is played through loudspeaker
    4. Test stimulus is calibrated & monitored by means of the reference microphone in the test box
    Monitors how much sound is going into the reference mic to ensure the correct input is used the entire time
    5. Test stimulus is amplified by hearing aid, and the HA output in the 2cc coupler is measured by the coupler microphone
    Needs a fresh battery, and HA on
    6. Test box software determines gain etc. from these measures
    Measures gain, distortion etc

Hearing Aids (2 decks)

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