Prescribing hearing aid performance

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Prescribing hearing aid performance

• Prescriptive procedure
• target
• threshold based procedures
• supra-threshold based procedures
• Evaluative procedure (comparative procedure)

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History of prescriptive methods

• Mirroring of the audiogram
• MCL
• Half-gain rule

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Suprathreshold Threshold

• Shapiro
• CID
• LGOB
• IHAFF/Contour
• ScalAdapt
• DSL i/o
• Mixed MSU

• NAL
• Berger
• POGO
• NAL-R
• POGO II
• NAL-RP
• Fig 6

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Prescription of gain-frequency response-linear (I)
POGO
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Prescription of gain-frequency response-linear
(II)
NAL , NAL-R NAL-PP Loudness equalization
intelligibility is assumed to be maximized when
all bands of speech are perceived to have the
same loudness

• Normal equal loudness curve
• LTASS
• 0.46 times the hearing threshold shape

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Prescription of gain-frequency response-linear
(III)

• DSL
• Targets it prescribes is real ear aided gain not
  insertion gain
• Especially for infants and young children
• Not loudness equalization, but make speech
  comfortable loud

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Example and comparison for POGO II, NAL-RP and DSL
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Example and comparison for POGO II, NAL-RP and
DSL
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Prescription of gain-frequency response
non-linear (I) LGOB
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Prescription of gain-frequency response
non-linear (II) IHAFF, contour and VIOLA
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Madsen Aurical method
ScalAdapt
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Prescription of gain-frequency response
non-linear (III) Fig 6
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Prescription of gain-frequency response
non-linear (IV) DSLi/o and NAL-NL1
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Comparison of procedures
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Prescribing compression thresholds
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Prescribing SSPL90

• General principles
• SSPL 90 must be low enough to avoid
  discomfort, damage and distortion, but must be
  high enough to avoid inadequate loudness and
  excessive saturation
• Type of limiting
• compression limiting or peak clipping

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SSPL90 prescription

• LDL based methods
• The reliability of LDL measurements
• Prediction LDL from threshold is difficult
• Correction factor from LDL to SSPL90
• LDL generally increase with stimulus bandwidth

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Variables associated with LDL measurements

• Instructions
• 1. A clear description of the purpose of the test
• 2. An explanation of why the test ins important
• 3. Terms and descriptions of loudness in common
  everyday language

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Initial discomfort Definite discomfort Extreme
discomfort
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Instruction for children
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Type of signals

• Speech (connected disclosure, spondee, sentences,
  nonsense syllable), pure tones, warble tones,
  narrow band of noise etc.
• No significant difference between stimulus types
  for the group data, no one signal should be
  regarded as the signal of choice when obtaining
  LDLs

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Procedures

• Clinician controlled procedures
• Simple up-down procedure
• Ascending approach
• Listener controlled procedures
• Method of adjustment
• Bekesy tracking method

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Predicting LDL from thresholds
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The NAL SSPL procedure
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Prescribing SSPL90 at different frequencies