Spatial attention in bilateral cochlear-implant users.

Area of Science:

• Auditory Neuroscience
• Speech Perception
• Neuroscience

Background:

• Cochlear-implant (CI) users experience significant challenges in understanding speech amidst background noise.
• Binaural unmasking, the ability to improve speech intelligibility using two ears, is crucial for effective auditory perception.
• The precise mechanisms limiting binaural unmasking in CI users remain unclear, with debate on peripheral versus central encoding contributions.

Purpose of the Study:

• To investigate whether the limitations in binaural unmasking for cochlear-implant (CI) users are attributable to peripheral or central auditory processing.
• To compare the binaural unmasking abilities of bilateral CI users with normal-hearing (NH) listeners under various acoustic conditions.

Main Methods:

• Speech intelligibility was assessed in bilateral CI users with their clinical processors and in NH listeners using unprocessed or vocoded speech.
• Stimuli were presented in monaural, diotic, and dichotic (opposite-ear) configurations to evaluate the effects of spatial separation between target speech and interfering sounds.
• Performance was measured across different listening conditions to quantify binaural unmasking benefits.

Main Results:

• All listener groups performed worst when target and interferer were presented monaurally or diotically (no spatial cues).
• Improved performance was observed when target and interferer were spatially separated (opposite ears) for both CI and NH listeners.
• However, CI users showed significantly smaller binaural benefits compared to NH listeners, especially in conditions simulating more realistic listening scenarios, with limited improvement when the interferer was diotic.

Conclusions:

• Cochlear-implant users can utilize spatial cues to direct attention towards a target sound when it is presented to one ear and the masker to the other.
• Significant limitations exist in achieving substantial binaural unmasking benefits for CI users in more complex listening environments.
• These limitations are likely rooted in the imprecise peripheral encoding of auditory information by the cochlear implant, rather than solely central processing deficits.