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

Cochlear implants provide people with severe hearing loss or deafness the
ability to acquire functional hearing by electrically stimulating the auditory
nerve fibers in the cochlea.
Current steering had created the possibility to stimulate nerve regions in
between electrodes. By stimulating two adjacent electrode contacts evenly, an
intermediate pitch percept is heard. The pitch can be shifted by shifting the
ratio of current being delivered to the two electrode contacts. Among others,
Snel-Bongers et al. (2012) has proven that virtual electrodes behave similar to
physical electrodes.
Sequential current steering provides an alternate means of inducing loudness
and pitch perception. Frijns et al. (2009) found similar excitation patterns
between simultaneous and compensated 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 Unpublished computational modelling work at our clinic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 sequentially
steered pulse trains in order to induce controllable loudness growth and the
perception of a single percept.

1. Snel-Bongers J, Briaire JJ, Vanpoucke FJ, Frijns JHM. Spread of excitation
and channel interaction in single-and dual-electrode cochlear implant
stimulation. Ear Hear. 2012;33(3):367-76.
2. Frijns JHM, Kalkman RK, Vanpoucke FJ, Bongers JS, Briaire JJ. Simultaneous
and non-simultaneous dual electrode stimulation in cochlear implants: evidence
for two neural response modalities. Acta Otolaryngol. 2009 Jan 8;129(4):433-9.
3. van Wieringen A, Carlyon RP, Macherey O, Wouters J. Effects of pulse rate
on thresholds and loudness of biphasic and alternating monophasic pulse trains
in electrical hearing. Hear Res. 2006 Oct 1;220(1-2):49-60.
4. Deeks JM, Carlyon RP, Epp B, Guérit F, Marozeau J. Effects of the relative
timing of opposite-polarity pulses on loudness for cochlear implant listeners.
J Acoust Soc Am. 2018 Nov 9;144(5):2751-63.

1.To assess if multiple sequentially steered pulses can reach appropriate
loudness while main-taining a single percept in cochlear implant subjects
2.To compare loudness growth of sequentially steered pulse trains with those of
conventional monopolar stimulation.
3.To assess if multiple sequentially steered pulses can reach appropriate
speech understanding in cochlear implant subjects.

A prospective single-centred cohort study will be conducted with a maximum of
three non-consecutive test days. A basal, a middle and an apical electrode pair
will be fitted with several different pulse train modalities. For each modality
the subjects will undergo conventional loudness balancing, loudness ranking and
loudness balancing tasks. Also, subjects will subjectively evaluate the sound
qualities of the most promising modalities.
If these tasks reveal a single loudness and pitch percept through pulse trains,
all electrode pairs may be fitted with the most promising modality and undergo
spectral tasks, temporal tasks and speech testing in a later phase.

Stimuli will be created with the Bionic Ear Data Collection System (BEDCS) of
Advanced Bionics (Valencia, CA) and administered through a Harmony CI Research
Processor (CE 0123, Valencia, CA) connected to a personal computer. Stimuli
will remain within the voltage compliance limits of the device.

The Harmony Research Processor has voltage compliance limits which will not be
exceeded and assure safe use. We will create and test variations of
conventional stimuli which have no higher risk or burden than the burden of a
clinical fitting. People may temporarily experience a light headache or a
temporarily return of suppressed tinnitus after listening to sound stimuli for
three hours. No other risks are known.
Subjects will not have a direct benefit through participation in this study.