Amplitude-mapping effects on speech intelligibility with unilateral and bilateral cochlear implants

Area of Science:

• Audiology
• Neuroscience
• Biomedical Engineering

Background:

• Bilateral cochlear implant (CI) users may experience overly loud sounds due to binaural loudness summation.
• Standard monaural amplitude-mapping may require adjustments for bilateral use to prevent overstimulation.

Purpose of the Study:

• To investigate the impact of amplitude-mapping adjustments on speech intelligibility in bilateral CI users.
• To assess speech perception in quiet and noise under unilateral and bilateral device use with adjusted maps.

Main Methods:

• Four amplitude maps were tested in eight bilateral CI users (Nucleus 24 system).
• Each map was used bilaterally for one week, followed by unilateral and bilateral speech testing in noise and quiet.
• Maps included a standard clinical map and three variations with reduced stimulation levels.

Main Results:

• Lowering stimulation levels resulted in a modest, statistically significant decrease in speech intelligibility (1-2 dB) in both quiet and noise.
• Altering map slope had minimal impact on performance.
• Bilateral use with unadjusted maps showed a modest but significant improvement over unilateral use in the S0N0 condition.

Conclusions:

• Higher stimulation levels in amplitude maps can enhance speech perception in quiet and noise for bilateral CI users.
• Binaural S0N0 advantage over the better ear can offset slight performance decreases from level adjustments for loudness summation.
• Clinical fitting of bilateral CIs should consider that adjusted performance may match or exceed better-ear-alone performance.