Modeling spectral-ripple discrimination by cochlear implant users

University Of Washington, Seattle WA

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Abstract

DESCRIPTION (provided by applicant): The overall objective of this research is to investigate the validity of the spectral-ripple discrimination test as a measure of spectral shape resolution in cochlear implant (CI) users. The spectral-ripple discrimination test is a time-efficient, nonlinguistic measure that is correlated with speech perception and music perception in CI users. However, there is controversy within the CI field about whether the spectral-ripple discrimination test actually does measure spectral shape resolution, and it has been suggested that information in just one or two CI channels may determine performance. The proposed project of research assesses the validity of these criticisms and of the spectral-ripple discrimination test as a measure of spectral shape resolution through a combination of psychophysical measures and a phenomenological model. The research program is built around the following two specific aims: 1) to evaluate the relationship of channel interactions and spectral-ripple discrimination in CI users, and 2) to model spectral-ripple discrimination in individual CI users. Sensitivity to spectral ripple is determined using the ripple phase reversal test, in which threshold is the ripple density (in ripples per octave) at which the listener can just detect, in a 3-interval oddball paradigm, a switch in the positions of the peaks and troughs of a spectrally modulated noise. Channel interactions are measured under the controlled conditions afforded by a research processor and are quantified by the interaction index, which measures how sensitivity to a probe electrode is affected by polarity inversions of simultaneous pulses on another electrode. Finally, the underlying mechanisms of spectral-ripple discrimination are examined through a phenomenological model that has the following inputs: the pulse trains generated by the patient's electrode array in response to rippled noise stimuli;a matrix of interaction indices measured for that patient;and channel weights. The findings of this project could, if appropriate, support broader clinical acceptance and use of the spectral-ripple discrimination test and, more generally, offer a framework for verifying psychophysical predictors of CI performance. PUBLIC HEALTH RELEVANCE: Despite successes achieved by deaf adults who have received a cochlear implant, such as average speech comprehension in quiet backgrounds of over 80%, outcomes are highly variable. Use of the spectral-ripple discrimination test, which has been shown to predict speech understanding, could help further development of technologies to improve performance. Acceptance of the test is limited, however, because the underlying mechanisms are not known precisely. The proposed project, an in- depth examination of the mechanisms of spectral-ripple discrimination, has significant implications in the area of rehabilitation of deafness and communication disorders.