How fitting, patient, and environmental factors affect directional benefit

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How fitting, patient, and environmental factors
affect directional benefit

• ???

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This directional benefit has been demonstrated
through both

• Word-recognition(??????)
• Self-report measures(???????)

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Brian Walden et al

• The Hearing Journal indicate that average
  hearing aid wearers report positive direction
  benefit in about a third of the listening
  environments they experience.

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The directional mode

• Provides less average output for sounds arriving
  from all angles than for sounds arriving from
  directly in front of the listener.

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eSNR

• The signal of interest is in front of the
  listener, the result is an improvement in
  effective signal-to-noise ratio for the
  direction mode.
• Directional benefit averaged across hearing aid
  wearers ranges from approximately 0 to more than
  70.

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Vast differences in directional benefit

• Compression
• Two omnidirectional microphones a single
  directional microphone
• Monaural binaural fitting
• The type of signal processing(analog or digital)

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compression

• No difference between linear and compression
  processing modes .
• However, compression parameters will interact
  with electroacoustic measures of directivity such
  as the front-to-back ratio(FBR).
• Therefore, compression parameters should be
  identified in the compilation of normative FBR
  data in clinical and research settings.

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Two omnidirectional microphones a single
directional microphone

• Stephen Thompson points out the use of a single
  directional microphone verus two omnidirectional
  microphones is an important design consideration.
• In practice, data suggest that optimization for
  maximum directivity is generally impacted much
  more by factors other than the number of
  microphones used.

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Monaural binaural fitting

• The directional benefit is similar whether the
  fitting is monaural or binaural.
• The binaural advantage is lost with monaural
  fittings, resulting in 20-30 poorer
  speech-recognition performance in both
  omnidirectional and directional modes when
  compared with binaural amplification.

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signal processing(analog or digital)

• The maximum improvement in eSNR is unaffected by
  the processing following the microphone, whether
  that processing is analog or digital.

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Fitting factors that impact benefit

• Frequency range of directivity
• Hearing aid style
• Venting
• Microphone orientation
• Low-frequency gain compensation

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Frequency range of directivity

• DI( directivity index).
• Variability exists both on average and in the
  frequencies where directivity is high.
• DI values among and within hearing aid models and
  manufacturers.
• Connected Sentence Test (CST)
• Speech intelligibility index (SII)

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Hearing aid style

• Quite similar for BTE ITE
• ITE style instruments is significatly less than
  that reported for BTEs.

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venting

• Allow low-frequency sounds originating from
  behind the listener to pass through the vent
  without attenuation.
• DI direction benefit are generally reduced
  with increasing vent size.

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Microphone port orientation

• Maximum directional benefit
• Other port orientations can disrupt the delay
  that is assumed to occur as port angle is
  impacted by the length of the earmold tubing.
• Fortunately, small deviation from the horizontal
  plane (approximately-10) do not significantly
  impact directivity, but larger deviations should
  be avoided.

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Low-frequency gain compensation

• Due to differences in their physical design,
  directional microphone hearing aids provide less
  low-frequency gain than their omnidirectional
  counterparts for sounds that arrive from the
  front.
• The closer together the ports, the higher the
  frequency at which gain reduction starts will be.

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Patient Factors

• The listening situations that patient are in .
• The magnitude of SNR loss.
• COSI
• HINT
• Quick-SIN

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Environment Factors

• Reverberation
• The number and position of noise sources
• Reflections from the same source that may arrive
  from various directions.
• Distance from the source increases, the
  proportion of reflected versus direct energy also
  increases.
• Effective critical distance(eCD).

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Summary

• How fitting factors might impact directional
  benefit.
• How hearing aid processing interacts with the
  patient and his or her listening environment.
• Optimize our counseling and offer the most
  appropriate listening strategies.