Sensitivity to envelope and pulse timing interaural time differences in prosthetic hearing

Binaural cues, such as interaural time difference (ITD), are pivotal for sound localization in the auditory system. However, contemporary cochlear implant (CI) processors convey only envelope ITD, neglecting pulse-timing ITD in the temporal fine structure, possibly contributing to CI users' spatial hearing challenges.To assess CI-implanted rats' sensitivity to envelope and pulse timing ITD, we utilized a stimulus involving a 900pps pulse train modulated by a 20 Hz sine envelope, allowing independent variation of PT_ITD and ENV_ITD {-0.1, 0, 0.1 ms}. Neural activity from the inferior colliculus (IC) in anesthetized neonatal deafened rats was recorded using a multi-channel silicon probe. Employing a Wiener filter method removed electrical artifacts, and analog multi-unit activity (AMUA) was computed over the onset response window (0-50 ms) and the baseline window (150-200 ms). 332 responsive multi-units, identified by peak amplitude exceeding the average plus 5 times the standard deviation of baseline window AMUA, showed 83% sensitivity to PT_ITD, with only one multi-unit sensitive to ENV_ITD. CI-implanted rats exhibited greater sensitivity to pulse timing ITD, highlighting potential for improved sound localization in CI users with a more effective ITD information strategy.