Bimodal Hearing

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Bimodal Hearing

• Peggy Liu
• B.A., Dip.Aud., M.Aud.

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The Benefits of Bimodal Hearing

• Speech Intelligibility
• Binaural redundancy
• Head diffraction
• Binaural squelch
• Localization Advantages
• Reduce of auditory deprivation

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The Benefits of Bimodal Hearing

• Binaural redundancy when speech and noise were
  presented from the same loudspeaker positioned at
  a fixed distance in front of the subject,
  binaural (bimodal) hearing is superior to
  monaural hearing

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The Benefits of Bimodal Hearing

• Head diffraction the effect of head diffraction
  has been measured by presenting speech and noise
  from spatially separated sources.

• These results were obtained when speech was
  presented nearer to the hearing aid side, and
  noise was presented nearer to the implant side.

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• These results were obtained when speech was
  presented nearer to the hearing aid side, and
  noise was presented nearer to the implant side.

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The Benefits of Bimodal Hearing

• Binaural Squelch no benefit on these with
  bimodal fittings.

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Functional Benefits

• Adult
• More natural sound
• Own voice quality is improved
• More speech-like sound quality
• Gets more directional sound
• H.A. picks up additional information
• Better localization
• Enjoy music more
• Easier to listen to speech in shops and
  restaurants
• Gives a better balance

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Functional Benefits

• Child
• Require less repetition
• More willing to converse with unfamiliar persons
• More confident in talking
• Initiate more conversation
• Speaks more clearly

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Clinical Issues

• Auditory experience
• A clinical question remained as to whether one
  should fit a hearing aid to a child or adult who
  didnt continue to wear a H.A. after C.I. surgery
  for some years.
• Ching et al.(2004) compared two groups one is
  habitually wore a HA with a CI, one is not. The
  results showed that after fitting a HA and given
  a period of 4-8 weeks, both groups derived
  binaural benefits from bimodal hearing compared
  to using a CI alone.

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Clinical Issues

• When start wearing the HA
• Recently research papers suggested that
  clinicians should suggest the patient to continue
  wearing HA soon after the CI surgery
• However, 3 months adaptive period with CI alone
  is reasonable if parents insist.

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Clinical Issues

• FM system
• When a binaural FM system with independently
  adjustable gain for each ear, the child would not
  be expected to gain any advantages from head
  diffraction or binaural squelch.
• However, the child would be able to derive the
  advantage arising from binaural redundancy and FM
  benefits.

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Clinical Issues

• CI alone If the situations below were happened,
  we should terminate the use of HA
• Consistent and prolonged rejection of the HA
  after the clinician has made every effort to
  fine-tune the fitting
• Patients functions better with a CI alone

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Optimizing a HA for a CI user

• Hearing aid optimization can be carried out soon
  after a stable MAP for the CI is established.
  Before optimization, the patient needs to have
  used the hearing aid for at least a few hours a
  day for 2-4 weeks.
• Prior to the hearing aid fine-tuning, ensure that
  an accurate fitting is achieved following these
  steps
• Assess hearing threshold levels
• Select a hearing aid using an NAL prescription
• Verify the fitting by insertion gain measurement
• Check the saturated OSPL 90 dB to ensure
  listening comfort

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Optimizing a HA for a CI user

• Frequency Response- Paired comparisons (HA alone)
  
• Connect hearing aid to programming device, set up
  two alternative frequency response (low frequency
  boost v.s. low frequency cut)
• A recorded story is then presented at
  conversational level, and the patient listens to
  the story using the two frequency responses, and
  then decides which one is better for
  understanding the story.
• Each alternative is compared with the NAL
  response for a number of times until a
  significant preference is obtained (8 out of 10)

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Optimizing a HA for a CI user

• Loudness Balancing- HA plus CI
• The patient listening to the story using the
  preferred frequency response in the HA, and then
  using the CI
• The patient compares the loudness in both ears,
  and decides whether speech amplified with the HA
  is louder, softer, or similar to the CI
• The HA gain is then adjusted until the patient
  finds both sides to be similar in loudness
• For linear HA, this test is carried out for an
  average input level for non-linear HA, this test
  can be carried out at more than one input level,
  and the compression characteristics of the HA can
  be adjusted accordingly.