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Amplification I > Lecture 11 > Flashcards

Lecture 11 Flashcards

1
Q

Regardless of the technology, features, accessories, or forms, hearing aids, we must achieve:

A

Audibility and comfort

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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)
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3
Q

What is vocal effort?

A

Variations of the LTASS

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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
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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
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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
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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.

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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

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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

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10
Q

What are 2 philosophies underlying prescriptive formulas?

A
  1. Loudness normalization
  2. Loudness equalization
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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

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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)

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13
Q

What are the 2 current researched, valid, and verified prescriptive methods?

A
  1. NAL-NL2 (National Acoustic Lab)
  2. DSL v5 (Desired Sensation Levels)
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14
Q

What is the NAL-NL2?

A
  • NAL-NL2 (National Acoustic Lab): the generally preferred methods for adult patients
  • Loudness Equalization strategy
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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)
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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. 1/2 gain rule
  2. POGO (prescription of gain and output)
  3. Berger
  4. NAL-R (first of the NAL)
  5. CID (central institute for the Deaf)
  6. 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
Q

Explain the DSL-v5

A
  • 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
Q

DSL-v5: age & etiology

A
  • 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
Q

DSL-v5: compression characteristics

A

The compression threshold is lower for milder losses and higher for more severe losses

28
Q

DSL-v5: listening environments

A

Listening environments: DSL targets assume that communicative speech is taking place in a quieter environments

29
Q

DSL-v5: bilateral fittings

A

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
Q

NAL-NL2 vs DSL: experience level

A

NAL-NL2: More initial gain for experienced users, less initial gain for new users

DSL: No correction for gain based on experience lvel

31
Q

NAL-NL2 vs DSL: gender

A

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
Q

NAL-NL2 vs DSL: bilateral vs unilateral fittings

A

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
Q

NAL-NL2 vs DSL: listening in noise

A

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
Q

NAL-NL2 vs DSL: loudness discomfort levels

A

NAL-NL2: Patient specific levels not taken into consideration

DSL: Alters gain if patient-specific are specified

35
Q

What does NAL-NL2 take into consideration?

A

An increased number of channels (more channels = slightly less gain) to mitigate the channel summation effect

36
Q

What formula is better?

A
  • 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
Q

Proprietary formulas (manufacturer specific formulas)

A
  • 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
Q

Verification of hearing aid targets with ____ rationales

A

Prescriptive

39
Q

When do we need to verify HA targets with prescriptive formulas?

A
  • 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

Amplification I (14 decks)

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