Bilateral cochlear implant (CI) patients face challenges in utilizing interaural time differences (ITDs). Our research on neonatally deafened (ND) CI rats revealed excellent ITD sensitivity even without early sensory input when CIs are synchronized. However, these rats exhibit abnormal temporal weighting functions (TWFs), showing reduced "onset dominance" to normal hearing (NH) subjects. This study explores the impact of hearing experience with jittered binaural input on the temporal weighting of pulses in ITD perception of ND CI rats.

Neonatal rat pups were deafened and bilaterally implanted with CIs as young adults. Subsequently, rats learned to lateralize ITDs (±{0, 40, 60, 80, 100, 120} μs) and interaural level differences (±{0, 1, 2, 3, 4, 5} dB) with each pulse receiving a random jitter between ±60 µs. Stimuli were presented at 250 pulses/sec. After 5 weeks of training, rats performed a temporal weighting test, with each pulse having a randomly selected ITD between ±120 µs. TWFs were calculated using multiple linear regression to determine the perceptual weight of each pulse.

In contrast to the onset weighting of ITDs observed in NH rats and ND rats with synchronized CIs, CI rats with jittered input during training showed no perceptual up-weighting of the first pulse, indicating no measurable precedence effect. Instead, TWF analysis revealed significant contributions from all pulses to the animals" lateralization decisions.

Behavioral results show that jittered input during initial training affects the temporal weighting of ITDs differently than described for NH listeners and rats with synchronized CIs. Our CI rats exhibited significant weighting of all pulses, suggesting that the auditory system averages ITDs across all pulses for lateralization decision.

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