Our research program is aimed at improving the use of physiological measures to predict perception with a cochlear implant (CI). The long-term goal is to objectively determine optimal speech-processor settings on an individual basis to improve speech understanding. Although some studies have shown modest correlations between objective and behavioral measures, these relations are not sufficiently strong to support exclusive use of physiological measures to predict behavioral outcomes. Recent studies have shown that the standard pulse polarity (cathodic-leading) used for CI stimulation is not ideal (e.g., Carlyon et al. 2013; Undurraga et al., 2010, 2013). Rather, more effective stimulation has been demonstrated using the opposite (anodic-leading) polarity for both physiological and perceptual measures. These findings raise significant questions about how to interpret the existing body of research aimed at relating physiological and perceptual measures, which used standard cathodic-leading pulses. Although the recent studies demonstrated greater effectiveness with anodic stimulation for both perceptual (i.e., louder percepts for a fixed current level) and physiological (i.e., shorter latencies, larger amplitudes, more effective masking) responses, no studies to date have examined polarity effects using standard clinical pulses, nor have any studies examined the relation between physiology and perception as a function of stimulus polarity. This is the goal of the present project. If polarity affects physiological measures to a different degree than perceptual measures, then the predictability of objective measures will be affected. In this project, we will examine the effect of stimulus polarity using clinically standard pulse shapes to determine the extent to which polarity affects perceptual and physiological measures, as well as the relation between the two. Examining the effects of stimulus polarity for standard pulse shapes will allow us to better understand the underlying physiological contributors to perceptual measures with CIs, and will have important implications for future clinical stimulation paradigms. Most importantly, results from this study will determine whether current clinical stimulation modes should shift from cathodic- to anodic-leading stimulation.
The primary goal of this project is to examine the effect of stimulus polarity on physiological and perceptual measures in cochlear-implant recipients. It is hoped that results from this project will lead to improvements in how well we can predict perceptual responses using objective physiological measures, potentially leading to better outcomes with the implant.
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