Abstract
In today’s cochlear implant (CI) systems, the monopolar (MP) electrode configuration is the most commonly used stimulation mode, requiring only a single current source. However, with an implant that will allow simultaneous activation of multiple independent current sources, it is possible to implement an all-polar (AP) stimulation mode designed to create a focused electrical field. The goal of this experiment was to study the potential benefits of this all-polar mode for reducing uncontrolled electrode interactions compared with the monopolar mode. The five participants who took part in the study were implanted with a research device that was connected via a percutaneous connector to a benchtop stimulator providing 22 independent current sources. The perceptual effects of the AP mode were tested in three experiments. In Experiment 1, the current level difference between loudness-matched sequential and simultaneous stimuli composed of 2 spatially separated pulse trains was measured as function of the electrode separation. Results indicated a strong current-summation interaction for simultaneous stimuli in the MP mode for separations up to at least 4.8 mm. No significant interaction was found in the AP mode beyond a separation of 2.4 mm. In Experiment 2, a forward-masking paradigm was used with fixed equally loud probes in AP and MP modes, and AP maskers presented on different electrode positions. Results indicated a similar spatial masking pattern between modes. In Experiment 3, subjects were asked to discriminate between across-electrode temporal delays. It was hypothesized that discrimination would decrease with electrode separation faster in AP compared to MP modes. However, results showed no difference between the two modes. Overall, the results indicated that the AP mode produced less current spread than MP mode but did not lead to a significant advantage in terms of spread of neuronal excitation at equally loud levels.
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Acknowledgments
The authors would like to thank The Hearing CRC and Robert Briggs, Bev Sheridan, Michelle Knight, Kerrie Plant, Nik Kydas, and John Heasman for their help and support in the clinical management of the participants, Michelle Moran and Arielle Umansky for supplying the clinic-tested speech scores, and finally the editor, Ruth Litovsky, and two anonymous reviewers for their helpful and insightful comments. This project was funded by The Garnett Passe and Rodney Williams Memorial Foundation and supported by Cochlear Ltd. The Bionics Institute acknowledges the support it receives from the Victorian Government through its Operational Infrastructure Support Program.
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Marozeau, J., McDermott, H.J., Swanson, B.A. et al. Perceptual Interactions Between Electrodes Using Focused and Monopolar Cochlear Stimulation. JARO 16, 401–412 (2015). https://doi.org/10.1007/s10162-015-0511-2
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DOI: https://doi.org/10.1007/s10162-015-0511-2