Magnified interaural level differences enhance binaural unmasking in bilateral cochlear implant users

Area of Science:

• Auditory Neuroscience
• Speech Perception
• Cochlear Implant Technology

Background:

• Bilateral cochlear implants (BiCI) offer potential binaural hearing benefits.
• BiCI users often experience limited access to interaural time difference (ITD) cues and reduced saliency of interaural level difference (ILD) cues.
• This limits the perceptual benefits of spatial separation between target and masker sounds.

Purpose of the Study:

• To investigate if magnifying ILD cues can improve masked speech intelligibility for BiCI listeners.
• To assess the effectiveness of ILD magnification in a symmetrical-masker configuration, where natural ILDs do not provide a long-term advantage.

Main Methods:

• ILD magnification was applied, which estimates moment-to-moment ITDs in octave-wide frequency bands.
• Corresponding ILDs were applied to target-masker mixtures at each ear, time, and frequency band.
• The study included experiments with normal hearing (NH) listeners using vocoded stimuli and with BiCI users.

Main Results:

• ILD magnification significantly improved speech intelligibility in both NH and BiCI listener groups.
• BiCI listeners did not benefit from spatial separation with natural ILDs, even with large separations.
• ILD magnification improved intelligibility without altering the monaural target-to-masker ratio (TMR) in either ear.

Conclusions:

• Magnifying ILD cues is an effective strategy to enhance masked speech intelligibility for BiCI users.
• The improvements are attributed to binaural effects, specifically increased perceptual separation of competing sound sources.
• This approach offers a promising avenue for improving auditory performance in challenging listening environments for individuals with bilateral cochlear implants.