[Processing of interaural time differences in normal-hearing subjects and cochlear implant users with FSP and HDCIS...

Area of Science:

• Auditory Neuroscience
• Human Auditory Perception
• Cochlear Implant Technology

Background:

• Sound localization is crucial for social interaction but remains a significant challenge for individuals with bilateral cochlear implants (CI).
• Investigating coding strategies that enhance temporal accuracy and source localization is essential for improving CI efficacy.
• Understanding interaural time difference (ITD) discrimination is key to addressing these challenges.

Purpose of the Study:

• To investigate the influence of fine structure processing (FSP) coding strategies on temporal accuracy and source localization in bilateral CI users.
• To objectively measure and compare the ability to discriminate between different interaural time differences (ITDs).
• To evaluate the utility of mismatch negativity (MMN) as an objective measure for ITD discrimination.

Main Methods:

• Recruited fifteen normal-hearing subjects and five CI users for the study.
• Employed electrophysiological recording of mismatch negativity (MMN) and psychoacoustic tests.
• Utilized headphones and loudspeakers to measure and compare ITD discrimination thresholds.

Main Results:

• Normal-hearing subjects exhibited an ITD discrimination threshold of 83-117 µs, with a significant MMN measured.
• CI users demonstrated a mean angle detection error exceeding 30° and a broad ITD discrimination threshold (1100-2100 µs).
• No clear MMN component was recorded in CI users due to artifacts, and localization ability was limited.

Conclusions:

• Mismatch negativity (MMN) serves as a reliable objective measure for ITD discrimination in normal-hearing individuals.
• This study did not find evidence that fine structure processing improves directional hearing in CI users.
• Further research is needed to enhance sound localization capabilities for bilateral CI recipients.