Optimisation of and mechanisms behind neural distortion responses obtained with cochlear-implant stimulation by interleaved pulse trains

Aligning the maxima of interleaved F1 and F2 amplitude-modulated pulse trains in cochlear-implant users yields the largest neural distortion responses, with both quadratic and cubic components present.

• Why it matters: Neural distortion responses reflect how electrically stimulated auditory nerve activity encodes temporal structure, but their generating mechanisms under interleaved AM stimulation are not fully understood.
• What they did: Across four CI-user experiments, the authors separated quadratic and cubic distortion products by manipulating the F1–F2 frequency relationship and relative AM phase, including shifting F2 phase and flipping the second pulse polarity; two computational auditory-nerve models were fit to the results.
• The result: Both quadratic and cubic distortion products were observed, NDR amplitude peaked when the 2 AM patterns’ maxima aligned, and anodic central pseudo-triphasic pulses increased responses in 4 of 9 users; modelling pointed to refractoriness over facilitation, but did not fully explain polarity-flip effects.

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