Fig 1.
Diagram representing stimulation modes of INT (left), EXT (mid) and COM (left) types, and their expected current paths.
(A) Bipolar, (B) Tripolar and (C) Common Ground belongs to the INT type; (D) Monopolar and (E); Current Steering belong to the EXT type; (F) partial-bipolar, (G) partial-tripolar and (H) Distributed All-Polar to the COM type. The stimulating and returning paths are presented by grey and black arrows, respectively.
Fig 2.
Representation of the Neuro Zti Cochlear implant.
Fig 3.
Schema representing the implant and the measuring system.
Fig 4.
(A) Distribution of the stimulation parameters across conditions. The conditions 1, 2, 3, and 5 were defined to be within the range of charge levels observed in routine clinical practice conditions [27]. The conditions 4 and 6 represented extreme stimulation charge levels (close to max system output, not observed in clinical practice) by increasing either stimulus amplitude or duration. (B) Table providing full description of the pulse characteristics used for all conditions.
Fig 5.
A, B, C. Oscilloscope recordings for electrodes E5 (stimulating), E6 and E10 (recording), a zoom of each recording is provided in the top-right small panels. (A) Oscilloscope view showing the pulse shape on the stimulating electrode (N, electrode E5), by converting the recorded voltage in current with the averaged clinical impedance of 3 kΩ. The arrow shows the measurement point on the oscilloscope trace, i.e., at the anodic phase offset, where the peak is maximum. (B) Oscilloscope view showing the raw voltage recorded on an adjacent returning electrode’s capacitor (N+1, E6). (C) Oscilloscope view showing voltage recorded on another adjacent returning electrode’s capacitor (N+5, E10). (D) Mock diagram of the electrode array and the respective places of electrode E5 (A), E6 (B) and E10 (C). The stimulating electrode was always E5.
Fig 6.
(A) Example of current returning distributions on the Intracochlear electrodes taken from the stimulating condition 3, electrode 8. The stimulating electrode, E8, is generating 100% of current and is not depicted in the diagram. (B) Resulting INT estimation (calculated from the sum of all intracochlear currents) and EXT (inferred from 100 minus INT). The symbols (*) show the electrodes out of the cochlea.
Fig 7.
Matrixes of current distribution from the different stimulating conditions.
The top left matrixes color-code shows percent of the generated current returning to each INT electrode (from 1 to 20), and their calculated returning to the reference EXT electrode (GND) for the stimulating condition 1. The other panels show the differences in current distribution between the stimulating conditions 2 to 6 and the stimulating condition 1.
Fig 8.
(A) Between stimulation condition, therefore averaged across electrodes. (B) Between electrodes, therefore averaged across repetitions and conditions. Error bars show standard error. Labels overlayed on the functions represents the stimulating conditions. The symbols (*) show the electrodes out of the cochlea.
Fig 9.
Example of returning current distributions from data pooled among stimulating conditions along the electrode array and for 6 different stimulating electrodes; E1, E4, E8, E12, E15, and E20.
Left panels of each maps represent the percent returning to the ground electrode, i.e., the EXT. Right panels represent the percent returning on each intracochlear electrodes (and if summed, the INT). The symbol (*) shows the electrodes out of the cochlea.
Fig 10.
Current distribution in ex-vivo measurement representing the intra- and extracochlear current returning to each electrode contact. The returning current is expressed as a percentage of current generated by the corresponding stimulating electrode. The double arrows are pointing to the electrodes 1–4, visually detected to be out of the cochlea. The symbol (*) shows the electrodes out of the cochlea.