Nonsimultaneous Rapid Pulse Trains (RaPiT) with Current Steering for Loudness Integration as a Basis for a new Loudness Encoding Strategy in Cochlear Implant Subjects

Sequential current steering provides an alternate means of inducing loudness and pitch perception. Frijns et al. (2009) found similar excitation patterns between simultaneous and com-pensated sequential stimulation in a computational model. The comparison of simultaneous and non-simultaneous current steering reveals that a patient cannot perceive differences between a single large pulse and multiple spatially or temporally separated smaller consecutive pulses when the spatial offset and/or temporal delay is small. Presenting pulse trains instead of single biphasic pulses can increase loudness perception without the need to increase the total amount of current per pulse (Van Wieringen et al., 2006). With this principle, it is hypothesized that a pulse train of several small pulses spaced by means of current steering can be perceived as similarly loud as a single larger pulse. Loudness growth will be also greater when a pulse phase is not directly compensated by the opposite-polarity phase, as is the case with conventional biphasic pulses (Deeks et al., 2018). Therefore, we will also create pulse trains where the opposite-polarity phases of the concurrent pulses will follow after all cathodic phases have stimulated the auditory nerve fibers. Unpublished computational modelling work at our clinic has established these pulse trains as a viable option for inducing loudness. Optimal characteristics of these pulse trains in terms of number of sequential pulses, pulse phase duration, interpulse interval and interpulse distance are unknown. This study aims to find the optimal characteristics for pulse trains with sequential current steering for loudness integration in order to induce controllable loudness growth and the perception of a single percept.

Nonsimultaneous current steered pulse trains will lead to a single pitch percept whilst reducing the amount of current in comparison to conventional monopolar stimulation

Three test sessions will be conducted

All subjects will undergo loudness balancing and loudness ranking procedures to objectively assess the loudness growth functions. Subjective assessment of sound quality will also be measured.