Using Current Steering to Increase Spectral Resolution in CII and HiRes 90K Users

Abstract

The HiResolution Bionic Ear has the capability of creating virtual spectral channels using current steering. Through simultaneous delivery of current to pairs of adjacent electrodes, it is hypothesized that the effective locus of stimulation can be steered to sites between the contacts by varying the proportion of current delivered to each electrode of the pair. Thus, theoretically, many intermediate regions of stimulation can be created with fine control over the proportion and amplitude of current delivered to each electrode. This study investigated the number of spectral channels-or different pitches-that could be resolved by adult users of the CII and HiRes 90K cochlear implants when current steering was applied to three pairs of electrodes along the implanted array. Subjects were postlinguistically deafened adults recruited from the general CII and HiRes 90K user populations at 11 participating study sites. After loudness balancing and pitch ranking electrode pairs (2 and 3, 8 and 9, 13 and 14), an adaptive paradigm was used to estimate the number of intermediate pitch percepts that could be heard for each pair when current steering was implemented. Those data were used to estimate the potential number of spectral channels for each electrode pair. Data from 57 implanted ears indicated that the numbers of spectral channels per electrode pair ranged from one (subjects who could not tell the electrodes apart) to 52 (an individual who had 52 different pitch percepts for the midarray pair of electrodes). The average numbers of spectral channels that could be distinguished were 5.4 for the basal electrode pair, 8.7 for the midarray electrode pair, and 7.2 for the apical electrode pair. Assuming that the average numbers of spectral channels for these three electrode pairs were representative of the entire 16-contact array, the potential total numbers of spectral channels could be estimated. For the 57 ears, the number of potential channels ranged from 8 to 466, with an average of 93. The HiResolution Bionic Ear has the ability to steer current through simultaneous stimulation of adjacent electrode contacts. These data show that the majority of subjects perceive additional spectral channels other than those associated with stimulation of the fixed electrodes when current steering is implemented. The results suggest that the average cochlear implant user may have significantly more place-pitch capability than is exploited presently by cochlear implant systems. Current steering will be implemented in a wearable sound-processing strategy that can deliver up to 120 spectral channels to CII and HiRes 90K recipients. The new strategy takes advantage of untapped capabilities of the CII/HiRes 90K implanted electronics and will be implemented through software, with no additional surgery required. It is anticipated that the improved spectral resolution offered by current steering will lead to better speech perception in noise and improved music appreciation.