This study compared pitch ranking, electrode discrimination, and electrically evoked compound action potential (ECAP) spatial excitation patterns for adjacent physical electrodes (PEs) and the corresponding dual electrodes (DEs) for newer-generation Cochlear devices (Cochlear Ltd., Macquarie, New South Wales, Australia). The first goal was to determine whether pitch ranking and electrode discrimination yield similar outcomes for PEs and DEs. The second goal was to determine if the amount of spatial separation among ECAP excitation patterns (separation index, Σ) between adjacent PEs and the PE-DE pairs can predict performance on the psychophysical tasks. Using non-adaptive procedures, 13 subjects completed pitch ranking and electrode discrimination for adjacent PEs and the corresponding PE-DE pairs (DE versus each flanking PE) from the basal, middle, and apical electrode regions. Analysis of d′ scores indicated that pitch-ranking and electrode-discrimination scores were not significantly different, but rather produced similar levels of performance. As expected, accuracy was significantly better for the PE-PE comparison than either PE-DE comparison. Correlations of the psychophysical versus ECAP Σ measures were positive; however, not all test/region correlations were significant across the array. Thus, the ECAP separation index is not sensitive enough to predict performance on behavioral tasks of pitch ranking or electrode discrimination for adjacent PEs or corresponding DEs.
The authors thank Lisa Stille, Gina Diaz, and Katelyn Glassman for assistance with data collection and analysis, Kendra Schmid, Ryan McCreery, and Walt Jesteadt for assistance with statistics and the d′ analyses, Gail Donaldson for consultation, and Tom Creutz for development of data collection programs. This study was supported by the National Institute on Deafness and Other Communication Disorders (NIDCD) Grants No. R01DC009595 and P30DC04662. The content of this project is solely the responsibility of the authors and does not necessarily represent the official views of the NIDCD or the National Institutes of Health.
I. INTRODUCTION II. METHODS A. Subjects B. Equipment setup C. Psychophysical stimuli and procedures 1. Loudness judgments 2. Loudness balancing 3. Pitch ranking 4. Electrode discrimination D. ECAP stimuli and procedures III. RESULTS IV. DISCUSSION