Sensitivity to interaural time differences with combined cochlear implant and acoustic stimulation

Area of Science:

• Auditory Neuroscience
• Audiology
• Biomedical Engineering

Background:

• Sound localization relies on interaural time differences (ITDs).
• Binaural hearing with a cochlear implant (CI) and a hearing aid (HA) presents unique challenges for ITD processing.
• Understanding ITD sensitivity in such users is crucial for improving auditory perception.

Purpose of the Study:

• To measure interaural time difference (ITD) sensitivity in individuals using a cochlear implant (CI) in one ear and a hearing aid (HA) in the other.
• To investigate the relationship between residual acoustic hearing and ITD perception.

Main Methods:

• Utilized a lateralization paradigm to measure just-noticeable differences (JNDs) in ITD.
• Stimuli included electric pulse trains (100 pps) from the CI and acoustic filtered click trains from the HA.
• Assessed acoustic hearing thresholds at 1,000 and 2,000 Hz.

Main Results:

• Four out of eight participants demonstrated measurable ITD JNDs, with median values ranging from 91 to 341 µs.
• Consistent ITD lateralization was only achieved by subjects with better than 100-dB SPL hearing thresholds at 1 and 2 kHz.
• A 1.5 ms delay of the electric signal was required for synchronous stimulation at the auditory nerves.

Conclusions:

• Binaural hearing with a CI and HA can support ITD perception, but only in a subset of users.
• Residual acoustic hearing significantly influences the ability to utilize ITD cues.
• Further research is needed to optimize electrical-acoustic stimulation for improved sound localization in CI users.