VCCA2020 SUBMITTED ABSTRACT
Authors: M.J. van Gendt1, M. Siebrecht1, J.J. Briaire1, S.M. Bohte2, J.H.M. Frijns1
1ENT-Department, Leiden University Medical Centre, PO Box 9600, 2300 RC Leiden, the Netherlands, 2CWI, Center for Mathematics and Informatics, Amsterdam, the Netherlands,
Corresponding author: M.J. van Gendt. Email-address: firstname.lastname@example.org
Background Despite the introduction of many new sound-coding strategies speech perception outcomes in cochlear implant listeners have levelled off. Computer models may help speed up the evaluation of new sound-coding strategies, but most existing models of auditory nerve responses to electrical stimulation include limited temporal detail, as the effect longer stimulus, such as adaptation, are not well-studied.
Method Measured neural responses to stimulation with both short (400 ms) and long (10 minutes) duration pulse trains were compared in terms of spike rate and vector strength with model outcomes obtained with different forms of adaptation (with a single decaying exponential, multiple exponentials, and a decaying power law). An adjusted previously published model combining biophysical and phenomenological approaches was used.
Results For long duration data, power law adaptation by far outperforms the single exponent model, especially when it is optimized per fiber. For short duration data, all tested models performed comparably well, with slightly better performance of the single exponent model for vector strength and of the power law model for the spike rates. The power law parameters obtained when fitted to the long duration data also yielded adequate predictions for short duration stimulation, and vice versa. The power law function can be approximated with multiple exponents, which is physiologically more viable. The number of required exponents depends on the duration of simulation; the 400 ms data was well replicated by two exponents (23 and 212 ms), whereas the 10-minute data required at least seven exponents (ranging from 4 ms to 600 s).
Conclusion Adaptation of the auditory nerve to electrical stimulation can best be described by a power law or a sum of exponents. This gives an adequate fit for both short and long duration stimuli, such as cochlear implant speech segments.