COMPARISON OF ELECTRODE DISCRIMINATION, PITCH RANKING, AND PITCH SCALING DATA IN POSTLINGUALLY DEAFENED ADULT COCHLEAR IMPLANT SUBJECTS

The goal of this study was to investigate the relationship between var iation in electrode site of stimulation and the perceptual dimensions along which such stimuli vary. This information may allow more effecti ve use of electrode place when encoding speech information. To achieve this goal, two procedures which measure pitch in subjects implanted w ith the Nucleus/Cochlear Corporation multichannel device were performe d. Estimates of electrode discriminability that can be obtained from t hese procedures were compared to a more direct measure of electrode di scriminability that was obtained in a previous study [Collins et al., Assoc. Res. Otolaryng. Abstracts, No. 642 (1994)]. In the first task, subjects performed a pitch ranking procedure similar to that used in p revious studies [Townshend et al., J. Acoust. Sec. Am. 82, 106-115 (19 87); Nelson et al., J. Acoust. Sec. Am. 98, 1987-1999 (1995)]. Estimat es of the pitch percept elicited by stimulation of each electrode as w ell as the discriminability of the electrodes were generated from the data using two different statistical analyses. In the second task, sub jects performed a pitch scaling procedure similar to one used in a pre vious study [Busby et al., J. Acoust. Sec. Am. 95, 2658-2669 (1994)]. Again, two different statistical analyses were performed to generate e stimates of the pitch percept corresponding to stimulation of each ele ctrode and to generate estimates of electrode discriminability. In gen eral, the estimates of the relationships between the pitch percepts ob tained from the two procedures were not identical. In addition, the es timates of electrode discriminability were not equivalent to the elect rode discrimination measures obtained from the same subjects during th e previous study. Signal detection theory has been used to model the d ecision processes required by each of the procedures described above [ e.g., Jesteadt and Bilger, J. Acoust. Sec. Am. 55, 1266-1276 (1974)]. However, these models do not predict the differences that were observe d between the data sets obtained during this study. An alternate model is proposed which may explain the data obtained from these subjects. This model is based on the assumption that the percept that is elicite d by electrical stimulation of an electrode is multidimensional, as op posed to unidimensional in nature. Therefore, the perceived signal is more appropriately modeled using a multidimensional random vector, whe re each element of the vector represents the perceived value of one of the dimensions of the signal. (C) 1997 Acoustical Society of America.