Effects of parameter manipulations on spread of excitation measured with electrically-evoked compound action potentials

Abstract

Objective: This study investigated the spread of excitation (SOE) profiles derived by eCAP measures and analysed the effects of various parameter settings. Design: SOE was measured using the forward masking technique (selectivity), as well as with a “fixed stimulus, variable recording” (scanning) technique. SOE profiles were produced at three current levels and at three sites along the array. Additionally, effects of the position of the recording electrodes and artefact rejection methods were studied in five subjects. Furthermore, correlation between SOE data and speech perception data was tested. All data were analysed using linear mixed models. Study sample: Measurements were performed intraoperatively in 31 users of the Advanced Bionics HiRes 90K cochlear implant. Results: The selectivity method produced narrower excitation profiles than the scanning method, showing an asymmetry along the array with wider SOE apically. Moreover, the position of the recording electrode shifted the SOE curves towards the recording contact, enhancing asymmetry. Neither significant effects of current level or artefact rejection methods were observed, nor a significant correlation with speech perception. Conclusions: SOE profiles obtained with the scanning method are wider than with the selectivity method. Both are insensitive to various parameter settings, although selectivity curves are shifted towards the recording contact.

Key Words::

• Cochlear implant
• eCAP
• electrode
• neural response imaging
• spread of excitation

Acknowledgements

The authors like to thank Ron Wolterbeek for statistical advice, Paul Boyd for language editing, Peter-Paul Boermans for ongoing support, and Advanced Bionics Corp., Valencia, California, USA and the Heinsius Houbolt Fund, The Netherlands for financial support. The data were presented under the title ‘Effects of parameter manipulations on spread of excitation measured with electrically-evoked compound action potentials’ at Objective Measures in Auditory Implants: 6th International Symposium, September 23, 2010, St Louis, Missouri, USA.

Declaration of interest: The authors report no conflict of interest. The authors alone are responsible for the content and writing of this paper.