Using Psychophysical Methods to Understand and Improve Speech Recognition in Cochlear Implant Users

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The long-term goal of the research is using a psychophysical approach to better understand how the auditory system responds to electrical stimulation via a cochlear implant (CI) and how we might use this knowledge to improve speech recognition outcomes with the device. There are three aims in the proposal; each has its clinical implications or applications. Together, they answer the broad question of why research efforts made to improve outcomes with CIs in the past have not produced appreciable or consistent benefits and what the possible solutions are. In aim 1, the central hypothesis is that there is a tradeoff relationship between temporal processing and spatial resolution of neural excitation, in a degenerated auditory system. The hypothesis will explain why focused electrode configuration aiming to improve spatial resolution has not provided consistent benefit. The idea is that the improvement in the spectral domain will impair processing in the temporal domain. Solution to the problem is proposed where focused stimulation should be applied in a subject- and channel- specific manner, such that focused stimulation should be avoided for given patients or given locations on the electrode array. In aim 2, a special CI patient population is studied, i.e., congenitally deafened subjects with no or little prior experience with acoustic hearing. These subjects may suffer from severe neural degeneration as a result of neonatal auditory deprivation. If implanted early, the broad and distorted CI stimulation may drive the naïve auditory system to mature in undesirable ways. Psychophysical evidences for these effects will be provided and alternative stimulation strategies are proposed and tested for this population. In aim 3, site- selection strategies that have been used in the past and produced highly variable outcomes, will be evaluated in the same subject sample. Site-selection strategies deactivate electrodes that are less “optimal”, based on various criteria. Comparing the selection measures in the same subject sample addresses the question of whether they assess similar attributes of the stimulation sites, and if not, which measure(s) might assess the important factor for speech recognition in electrical stimulation. Aim 3 also evaluates the efficacy of using psychophysical testing as a potential auditory training method. Psychophysical testing offers several advantages over musical training or training with the speech stimulus itself. The proposed experiments, offering explanations and solutions for the existing problems with CIs, have direct and immediate clinical implications.