Improved binaural stimulation strategy for bilateral cochlear implants

Harvard Medical School, Boston MA

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Abstract

? DESCRIPTION (provided by applicant): Bilateral cochlear implant (CI) users have poor perceptual sensitivity to interaural time differences (ITD) of high-rate periodic pulse trains (>30 pps), which are used as carriers in modern CI processors. As a result, CI performance is degraded for tasks that are dependent on binaural cues such as sound localization and speech reception in noisy environments. Therefore, there is a need for new CI processing strategies that improve perceptual ITD sensitivity. Introducing binaurally coherent jitter into high-rate puls trains has been shown to improve ITD sensitivity in CI users, and neural correlates of this effect have been observed in the inferior colliculus (IC). Neurons in the IC respond weakly and with poor ITD sensitivity to high-rate periodic pulse trains, but jittered trains contain occasional shot inter-pulse intervals (IPIs) that can elicit spikes in adapted neurons, thereby increasing the firig rate and restoring ITD sensitivity. We will test the concept of a new processing strategy in this proposal aimed at improving both perceptual and neural ITD sensitivity with bilateral CI. In this strategy, extra pulses are inserted into periodic pulse trains to introduce short IPIs at specific time points in the stimulus. In Aim 1, we will determine the effect of short IPIs on ITD sensitivit of IC neurons using an awake animal model of bilateral CIs. Our preliminary data suggest short IPIs can improve neural ITD sensitivity, and we will investigate what stimulus parameters of short IPIs optimize this improvement across the population of IC neurons. In Aim 2, we will introduce short IPIs into pulse trains that are amplitude modulated by speech envelopes to approximate the stimuli delivered by clinical CI processors. We will again characterize neural ITD sensitivity in IC neurons in our animal model, which will allow us to investigate how short IPIs could be incorporated into a clinical stimulation strategy. Preliminary data suggest short IPIs can increase neural ITD sensitivity with modulated pulse trains. Lastly, in Aim 3 we will evaluate the effect of short IPIs on perceptual ITD discrimination with a classical conditioning task in our animal model. We predict that the animals will more readily discriminate the ITD of high-rate pulse trains when they contain short IPIs. The overall goal of these experiments is to evaluate the potential for a novel stimulation strategy that uses short IPIs to improve perceptual ITD sensitivity. This strategy could lead to better outcomes for CI users by improving sound localization and speech reception in noisy environments.