Lecture 11 Flashcards
1
Q
Regardless of the technology, features, accessories, or forms, hearing aids, we must achieve:
A
Audibility and comfort
2
Q
What is the LTASS?
A
- Long-term average speech spectrum
- We need to look at speech spectrum (where speech falls on the audiogram)
3
Q
What is vocal effort?
A
Variations of the LTASS
4
Q
What is speech mapping?
A
- Depending on frequency and audiogram configuration we get a computer-generated gain target for each frequency
- Different target points to hit for our gain
5
Q
What are the underlying principles of the HA prescriptive method?
A
- Prescribed gain value (target gain), is calculated (using a formula) for each frequency (based on audiometric data)
- The audiometric data will indicate which target we need to match
6
Q
How was gain calculated before digital HAs?
A
- Before the inception of digital devices, target gain was calculated at each audiometric frequency using tables for calculation
- Done prior to the hearing aid selection
7
Q
How is gain calculated today?
A
Today, digital hearing aids have flexible frequency responses and the prescriptive formulas are included within the fitting software and verification equipment.
8
Q
What does a linear prescriptive formula provide?
A
A linear prescriptive formula gives a single fixed amount of gain regardless of the input up to the point of saturation
9
Q
What does a non-linear prescriptive formula provide?
A
A non-linear prescriptive formula gives different amount of gain dependent of the input
- Target gain for soft, average, and loud speech
- Compression
10
Q
What are 2 philosophies underlying prescriptive formulas?
A
- Loudness normalization
- Loudness equalization
11
Q
What is loudness normalization?
A
Gain prescribed = gain need for the person with hearing loss to rate the sound level the same as it would be rated by people with normal hearing
12
Q
What is loudness equalization?
A
Gain prescribed = gain need to amplify all speech frequency bands to perceived equal loudness (consonants just as aloud as the vowels)
13
Q
What are the 2 current researched, valid, and verified prescriptive methods?
A
- NAL-NL2 (National Acoustic Lab)
- DSL v5 (Desired Sensation Levels)
14
Q
What is the NAL-NL2?
A
- NAL-NL2 (National Acoustic Lab): the generally preferred methods for adult patients
- Loudness Equalization strategy
15
Q
What is the DSL v5?
A
- DSL v5 (Desired Sensation Levels): the generally preferred methods for pediatric patients
- Loudness Normalization strategy (keeping balance between how a normal hearing listener would hear sound)
16
Q
What are prescriptive methods the starting point for?
A
Prescriptive methods are the starting point to determine gain and frequency response (always manipulate based on patient preference)
17
Q
What are the 6 historical prescriptive methods?
A
- 1/2 gain rule
- POGO (prescription of gain and output)
- Berger
- NAL-R (first of the NAL)
- CID (central institute for the Deaf)
- DSL (first of the DSL)
These were linear methods
18
Q
Explain the 1/2 gain rule
A
- 1940s
- Gain prescribed = hearing threshold X 0.5 for each frequency
- Didn’t consider the speech spectrum, was not suitable for severe to profound loss
- (Example: If a threshold was 105 dB HL, gain (105 x 0.5 = 53 dB of Rx gain)
- Input of 50 dB, adding 53 dB of gain = 103 dB output
- Not audible
- Not a fantastic method, but one of the first methods used
19
Q
Explain the POGO
A
- 1980s
- POGO (Prescription of Gain and Output)
- Frequency specific gain calculation (gain has variation depending on the frequency)
- Gain = (Threshold x 0.5) -10 dB at 250 Hz
- Gain = (Threshold x 0.5) -5 dB at 500 Hz
- Gain = Threshold x 0.5 at other frequencies
- Still, no consideration of the speech spectrum, and may not be suitable for severe to profound hearing losses
20
Q
Explain the berger method
A
- 1980s
- Speech spectrum considered (one of the first methods where this was considered)
- Variable gain at different frequencies with an emphasis on those important for speech discrimination (we can weight frequency gain differently to help hear specific speech)
21
Q
Explain the NAL
A
- 1970s
- NAL and NAL-R(revised) NAL-RP(revised for profound losses)
- National Acoustic Labs (first established as the Commonwealth Acoustics Lab) began to service war vets and children in 1947
- Formula attempting to all speech frequency band to equal loudness (to maximize intelligibility)
- Revisions included adjustments for
- LF gain reduction to minimize the effects of background noise
- Minimize excessive gain in HF for steeply sloping losses
22
Q
Explain the CID
A
- 1980s
- Central Institute for the Deaf Method (CID)
- Speech spectrum introduced with frequency-specific, measured patient MCLs (this was the first time patient MCL was considered)
- Amplify average speech spectrum to the MCL from frequencies between 500-4000 Hz
- 250 Hz, speech spectrum was amplified to half-way between threshold and MCL in an attempt to reduced BGN
23
Q
Explain the DSL
A
- 1980s
- Desired Sensation Levels- work out of Western University and Dr. Richard Seewald
- Rationale was similar to the CID method
- Initially developed for pediatric patients to create a loudness normalization approach with providing good audibility for speech.
- More initial gain compared to the first versions of NAL (a little bit louder for pediatric patients)
- Gain: what is required to amplify the average speech spectrum to a desired level above thresholds without exceeding LDL
- This method came about because of rubella (which caused acquired pediatric HL)
- This was a normalization method
24
Q
Explain the NAL-NL2
A
- Speech intelligibility and loudness comfort
- Latest version released in 2011, idealized for fitting hearing instruments with WDRC
- Comparative to the NAL-NL1 version, hearing aid users were prescribed an average of 3dB less gain overall
- Focus on tonal and non-tonal language (Tonal languages pitch contours of syllables distinguish one word from another, whereas in non-tonal languages pitch is used to convey intonation. Li et al, 2021)
- Gender differences (males prescribed more gain that females)
25
Explain the DSL-v5
- Speech intelligibility and loudness comfort
- The DSL method, coming out of work from University of Western Ontario (in the mid 1980s) aimed to provide clinicians with a systematic, science-based approach to pediatric fittings (text, page 533)
- Optimize speech recognition for children with hearing loss, bring speech to a desired sensation level to maximize intelligibility
- Speech is amplified across a broad range of frequencies to support auditory learning and make speech cues audible
26
DSL-v5: age & etiology
- Age and Etiology: Patient age and cause of hearing loss is considered
- Higher listening level for paediatric (presumed congenital) than for adults (assumed acquired). A reduction of approximately 7dB is applied for adults
27
DSL-v5: compression characteristics
The compression threshold is lower for milder losses and higher for more severe losses
28
DSL-v5: listening environments
Listening environments: DSL targets assume that communicative speech is taking place in a quieter environments
29
DSL-v5: bilateral fittings
Bilateral Fittings: correction factor when fitting bilateral technology, reducing speech targets by 3dB. Bilateral sloping losses get a boost in the mid frequencies and a decrease in high frequency gain
30
NAL-NL2 vs DSL: experience level
NAL-NL2: More initial gain for experienced users, less initial gain for new users
DSL: No correction for gain based on experience lvel
31
NAL-NL2 vs DSL: gender
NAL-NL2: Irrespective of hearing loss or experience, reduces gain on average for females than males (2dB)
DSL: No adjustments in gain based on gender
32
NAL-NL2 vs DSL: bilateral vs unilateral fittings
NAL-NL2: Gain correction changes for bilateral fittings based on input (-2dB for low imput and up to 6dB for high input)
DSL: -3dB decrease across input levels for bilateral fittings vs unilateral fittings
33
NAL-NL2 vs DSL: listening in noise
NAL-NL2: No correction factors for listening in noise
DSL: -3 to -5dB reduction for low importance frequencies (to do this, the REM system has to allow this)
34
NAL-NL2 vs DSL: loudness discomfort levels
NAL-NL2: Patient specific levels not taken into consideration
DSL: Alters gain if patient-specific are specified
35
What does NAL-NL2 take into consideration?
An increased number of channels (more channels = slightly less gain) to mitigate the channel summation effect
36
What formula is better?
- The best comparison we have in study was conducted by Johnson and Dillon (2011) - not real humans, just math calculations:
- 7 different audiometric types (5 SNHL, and 2 conductive loss profiles)
- Compared predicted loudness perception, cochlear excitation, audibility, speech intelligibility, conversation ability in quiet and background noise
- Results: overall loudness was similar, similar speech intelligibility in quiet and BGN
37
Proprietary formulas (manufacturer specific formulas)
- Many manufacturers have their own prescriptive formulas that are often based on DSLv5 or NAL-NL2 but with brand specific variations to suit the specific products that they offer
- Some examples: eSTAT, WFA (Starkey), Phonak Adaptive Digital, WFR (Widex Fitting Rationale), VAC (Oticon Voiced-Aligned Compression), Audiogram+ (Resound)
- Benefits and Pitfalls?
- Manufacturers get this data from their HA users
- The manufacturer specific formulas can be good, but they aren’t specifically verified
38
Verification of hearing aid targets with ____ rationales
Prescriptive
39
When do we need to verify HA targets with prescriptive formulas?
- When verifying HA targets with prescriptive formulas, we also need to do that when there are audiogram changes for patients
- When audiogram changes, reverify the prescription
