The reliability of aided soundfield thresholds in nonlinear hearing aids

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The reliability of aided sound-field thresholds
in nonlinear hearing aids

• The Hearing review 2004.12
• By Francis Kuk, PhD Denise Keenan, Ma
• ??????

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• The aided sound-field threshold (ASFT) represents
  the softest sound that the wearer can hear inside
  the audiometric test booth when using a hearing
  aid.

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• For a wide dynamic range compression (WDRC)
  hearing aid without a volume control (VC), the
  aided threshold approximates the softest sound
  that the wearer hears in real-life listening
  situations

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Factors Affecting ASFTs

• Noise
• Standing waves
• Head and body movement
• Nonlinear hearing aids

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Suggestions for Measuring ASFTs

• Always conduct sound-field measurements in a
  quiet, minimally reflective sound-booth.
• Use standardized instructions for all listeners

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• If a VC is present on the hearing aid, make sure
  that its position is marked so it may not be
  intentionally or unintentionally changed during
  testing.

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• Walker et al.15 suggested that keeping the
  subjects head in a fixed position would improve
  the reliability of sound-field measurement.

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• Make sure that the measured aided thresholds are
  meaningful
• The hearing aid has a high circuit-noise
  level
• The listener has little or no hearing loss
• especially in the low frequencies
• The hearing aid is in a fixed directional
• microphone mode.

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• Compression time constants. Use modulated
  sinusoids that are 1-2 seconds in duration and an
  inter-stimulus interval that is longer than the
  release time of the nonlinear hearing aid.

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• Noise reduction. Use modulated sinusoids that are
  shorter than the activation time of the noise
  reduction algorithm. Typically, stimuli that are
  1-2 seconds in duration are short enough for most
  noise reduction algorithms to remain inactive.

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• Active feedback cancellation.Typically, a 1-2
  second stimulus duration is acceptable. In
  addition, random inter-stimulus intervals should
  be used to avoid patterning.

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• Directional microphones It is important to check
  with the manufacturer of the specific adaptive
  microphones to appraise how the adaptation time
  of the specific microphone may affect the
  accuracy and reliability of the ASFT.

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Thanks for your attention!!