Loudness and pitch perception using Dynamically Compensated Virtual Channels

Abstract

Reducing power consumption is important for the development of smaller cochlear implant (CI) speech processors. Simultaneous electrode stimulation may improve power efficiency by minimizing the required current applied to a given electrode. Simultaneous in-phase stimulation on adjacent electrodes (i.e. virtual channels) can be used to elicit pitch percepts intermediate to the ones provided by each of the physical electrodes in isolation. Virtual channels are typically implemented in monopolar stimulation mode, producing broad excitation patterns. Focused stimulation may reduce the excitation patterns, but is inefficient in terms of power consumption. To create a more power efficient virtual channel, we developed the Dynamically Compensated Virtual Channel (DC-VC) using four adjacent electrodes. The two central electrodes are current steered using the coefficient α (0 < α < 1) whereas the two flanking electrodes are used to focus/unfocus the stimulation with the coefficient σ(−1<σ<1). With increasing values of σ, power can be saved at the potential expense of generating broader electric fields. Additionally, reshaping the electric fields might also alter place pitch coding. The goal of the present study is to investigate the tradeoff between place pitch encoding and power savings using simultaneous electrode stimulation in the DC-VC configuration. A computational model and psychophysical experiments in CI users have been used for that purpose. Results from 10 adult Advanced Bionics CI users have been collected. Results show that the required current to produce comfortable levels is significantly reduced with increasing σ as predicted by the computational model. Moreover, no significant differences in the estimated number of discriminable steps were detected for the different values of σ. From these results, we conclude that DC-VCs can reduce power consumption without decreasing the number of discriminable place pitch steps.

Dynamic Current Focusing Compared to Monopolar Stimulation in a Take-Home Trial of Cochlear Implant Users

“…To the best of our knowledge, only Arenberg et al (2018) and Nogueira et al (2017) have investigated similar dynamic focusing configurations, although Nogueira’s work involved virtual channels and added current steering through quadrupolar stimulation instead of physical electrodes. Because Nogueira et al combined focusing with steering and did not conduct speech or spectro-temporal testing, we cannot directly compare the performance of their strategy to the dynamic strategies of Arenberg (2018) and de Jong (2019a, 2019b).…”

Dynamic Current Focusing: A Novel Approach to Loudness Coding in Cochlear Implants

“…Despite the reduced level of current focusing, pTP stimulation improves spectral ripple discrimination (Berenstein et al 2008;Smith et al 2013), while speech perception showed to be improved in some (Srinivasan et al 2013;Wu & Luo 2013), but not in all studies (Berenstein et al 2008;Bierer & Litvak 2016). Nogueira et al (2017) developed a stimulation mode called the dynamically compensated virtual channel in which four adjacent electrodes are stimulated simultaneously to decrease power consumption. Although this quadrupolar strategy saves power, it also generates broader electrical fields, specifically at higher loudness levels.…”

A phenomenological computational model of the evoked action potential fitted to human cochlear implant responses

“…Currently, there are different computational models of CIs that have been fitted using clinical data, such as transimpedances, cochlear dimensions, electrode locations, and loudness and pitch perception [ 10 , 25 , 27 , 28 ], and speech understanding [ 29 ]. Additionally, there are other models that simulate ECAPs responses [ 14 , 16 , 22 , 30 – 32 ] as the one proposed in this work.…”