Localization and interaural time difference (ITD) thresholds for cochlear implant recipients with preserved acoustic...

Area of Science:

• Audiology
• Neuroscience
• Biomedical Engineering

Background:

• Cochlear implants (CIs) aim to restore hearing, but spatial hearing remains a challenge.
• Hearing preservation in CI recipients offers potential for improved binaural hearing.
• Interaural time difference (ITD) cues are crucial for sound localization.

Purpose of the Study:

• To investigate horizontal plane sound localization and ITD thresholds in adult CI users with hearing preservation.
• To compare localization performance across different aided conditions: bilateral hearing aids, bimodal (CI + contralateral hearing aid), and best aided.
• To explore the relationship between ITD sensitivity, localization, and hearing preservation.

Main Methods:

• 14 adult CI recipients with hearing preservation participated.
• Sound localization was assessed using broadband noise in an anechoic chamber with a 33-loudspeaker array.
• Interaural time difference (ITD) thresholds were measured using low-frequency tones and bandpass noise under headphones.

Main Results:

• Localization performance, measured by root-mean-square error, was significantly poorer in the bimodal condition (60.2°) compared to bilateral hearing aids (46.1°) and best aided (43.4°).
• ITD thresholds in CI recipients were highly variable (43 to >1600 μs), with some falling within the normal range.
• ITD thresholds significantly correlated with localization accuracy, interaural low-frequency hearing asymmetry, and speech reception threshold (SRT) benefit.

Conclusions:

• Cochlear implant recipients with hearing preservation can access binaural cues.
• Sensitivity to ITDs is a significant predictor of sound localization ability in this population.
• The degree of hearing preservation positively influences the benefit derived from binaural hearing with cochlear implants.