While cochlear implants have been successful in enabling speech understanding in people who have severe-to-profound hearing loss, performance in tasks such as locating the direction of a sound and speech understanding in noise remains challenging. These tasks are aided with binaural hearing in people with normal hearing, but bilateral cochlear implantation has not provided the same degree of benefit. Much of this deficit arises from the way sounds are converted into electrical stimulation in modern day cochlear implants (CIs). Modern CIs operate by dividing the incoming acoustic signal into a number of channels and encoding each channel with a constant high-rate electrical pulse train. This processing is known to affect sensitivity to interaural time differences (ITDs), a binaural cu important for sound localization and speech understanding in noisy situations. In bilateral CI users, a conundrum exists where good ITD sensitivity occurs with low rates of stimulation but better speech understanding requires high rates of stimulation. Proposed solutions typically mix rates of stimulation at different channels, where low rates are used in low frequency channels while high rates are used in high frequency channels. This approach assumes that ITDs, a dominant cue at low frequencies in normal hearing listeners, should be presented where the cochlea is most sensitive to low frequencies. However, measurements of ITD sensitivity in bilateral CI users show that this assumption may not necessarily hold true, suggesting that alternate approaches can be considered for presenting ITDs in CIs. The objective of this research is to measure the extent to which bandlimited frequency modulations (FM) encoded within a high-rate electrical pulse train can increase binaural hearing benefits in bilateral CI users. In contrast to solutions that use mixed stimulation rates, the novelty of encoding FM is that ITD cues can be presented on all channels and thereby maximize ITD sensitivity in all CI users. The goal of this work will be to demonstrate the feasibility of using FM encoding to improve the binaural hearing abilities of bilateral CI users, an outcome that has not been achievable to date. Our focus will be on determining optimal FM parameters for maximizing ITD sensitivity in bilateral CI users. Improving the binaural hearing abilities of bilateral CI users wll have a positive impact on how they interact in everyday listening situations, by decreasing fatigue when conversing in noisy environments, and improving learning outcomes in children with bilateral CIs by helping to direct attention in a noisy classroom. In addition, the results obtained from these experiments may influence signal processing developments in other auditory implantable prostheses such as auditory mid-brain and brainstem implants.
People with bilateral cochlear implants often find it challenging to locate the source of sound, or to understand speech in noisy situations, which can have a negative impact on their daily life. This project will investigate the novel encoding of frequency modulations in a speech processing strategy in order to enhance the binaural hearing abilities of patients with bilateral cochlear implant. Innovative methods will be employed to measure the extent to which performance is improved by this new strategy, as well as provide tools for tailoring processing strategies to the patient.
| Goupell, Matthew J; Stoelb, Corey A; Kan, Alan et al. (2018) The Effect of Simulated Interaural Frequency Mismatch on Speech Understanding and Spatial Release From Masking. Ear Hear 39:895-905 |
| Kan, Alan (2018) Improving Speech Recognition in Bilateral Cochlear Implant Users by Listening With the Better Ear. Trends Hear 22:2331216518772963 |
| Litovsky, Ruth Y; Goupell, Matthew J; Kan, Alan et al. (2017) Use of Research Interfaces for Psychophysical Studies With Cochlear-Implant Users. Trends Hear 21:2331216517736464 |
| Kan, Alan; Jones, Heath G; Litovsky, Ruth Y (2016) Lateralization of interaural timing differences with multi-electrode stimulation in bilateral cochlear-implant users. J Acoust Soc Am 140:EL392 |
