Contribution
Insights into the periodicity encoded by amplitude modulation and short inter-pulse intervals using a phenomenological auditory-nerve model
* Presenting author
Abstract:
Cochlear implants (CIs) are neural prostheses that partially restore hearing in the profoundly hearing-impaired or deaf. CIs convert the acoustic input into sequences of pulse trains that directly stimulate the auditory nerve through an intracochlear array of electrodes. Clinical stimulation strategies largely rely on constant-rate pulse train carriers that code periodicity by means of amplitude modulation and crucially rely on its depth for perceptual salience. Recently, we have shown that inserting extra pulses with short inter-pulse intervals (SIPI pulses) at modulation peaks of such pulse trains improved periodicity (i.e., temporal-pitch) coding. Based on animal data, the SIPI effect has been attributed to modulation enhancement. In this contribution, we used a phenomenological model of an auditory-nerve neuron by Takanen and Seeber [Trends Hear 26, 233121652211170 (2022)] to examine modulation-based single-electrode periodicity coding both with and without SIPIs. We show that SIPIs introduce a form of asymmetric modulation enhancement, emphasizing the modulation peak while largely suppressing the modulation offset, possibly as a combination of enhanced facilitatory and refractory effects. Furthermore, we show how periodicity coding changes when stimulating with two neighboring electrodes with identical pulse trains and varying between-electrode delays instead of a single electrode.