# Interactions of Interaural Time and Level Differences in Spatial Hearing with Cochlear Implants

## TL;DR

This study shows that timing differences are more important than loudness differences for spatial hearing in cochlear implant users.

## Contribution

It reveals how early deafened rats use both timing and loudness cues, with timing being dominant, for sound localization after cochlear implantation.

## Key findings

- Rats with cochlear implants are highly sensitive to both ITDs and ILDs.
- Timing differences are weighted more heavily than loudness differences in spatial hearing.
- Early deafened rats combine ITD and ILD information in a weighted sum for lateralization.

## Abstract

Normally hearing humans can localize sound sources quite accurately, with minimum audible angles as small as 1°. To achieve this, these auditory pathways combine information from multiple acoustic cues, including interaural time and interaural level differences (ITDs and ILDs). Patients relying on cochlear implants (CIs) to hear the world do not match normal performance. These deficits are most pronounced in patients with little or no hearing experience early in life, and they appear to result from impaired sensitivity to ITDs, but not to ILDs. However, little is known about how ITD and ILD sensitivities develop and interact in an early deafened auditory system shortly after CI implantation. neonatally deafened rats with bilateral CIs are fitted, and, providing informative ITDs and ILDs from stimulation onset, trained them to lateralize CI stimuli. These animals are exquisitely sensitive to both ILDs and ITDs of CI stimulus pulses, and combined information from both cues in a weighted sum. Importantly, ITDs are weighted heavily in the CI rats, such that only very modest ITDs pointing in one direction can confound quite large ILDs pointing in the opposite direction. This underlines the importance of informative ITDs for maximizing the potential for spatial hearing with CI devices.

Differences in timing (ΔT) are weighted heavily compared to differences in loudness (ΔL) in binaural hearing with cochlear implants.