Temporal pitch processing in an animal model of normal and electrical hearing

Abstract

Cochlear-implant users typically exhibit only limited sensitivity to temporal fine structure (TFS). We are developing a cat animal model in which to explore alternative modes of electrical stimulation that might improve TFS sensitivity. Normal-hearing cats were trained to detect changes in rates of acoustical pulse trains. The pulses were non-resolved harmonic complexes that were band-limited to stimulate the basal cochlear turn, which is the location that is accessible to feline cochlear implants. The rate sensitivity of that temporal pitch was like that of human listeners but shifted upward in rate by ∼1 octave. Scalp recordings from sedated cats showed a frequency following response (FFR) across all tested rates, up to 600 pulses per second. Changes in pulse rates elicited an Acoustic Change Complex (ACC) that showed a rate sensitivity parallel to that of perception. That suggests that the ACC can be used as a surrogate for psychophysical performance. Cats that were implanted chronically with conventional intra-scalar cochlear implants exhibited electrically-evoked FFR and ACC that showed rate sensitivity largely similar to that in normal-hearing cats. These results validate the cat animal model for ongoing studies of transmission of TFS with electrical cochlear stimulation. [Work supported by the NIDCD and the Wellcome Trust]