Limitations on temporal processing by cochlear implant users

Abstract

Two experiments studied the deterioration in rate discrimination and pitch perception for pulse trains presented to single electrodes at high pulse rates. The first measured rate discrimination DLs (“RDLs”) for 100-pps and 400-pps standard rates, for each of 4–5 electrodes and for 10 Advanced Bionics cochlear implant users. Thresholds were measured using two interleaved adaptive tracks, corresponding to the 100- and 400-pps standard rates. Gap detection thresholds (“GDTs”) for a 1031-pps pulse train were also measured. There was a highly significant across-subject correlation between GDT and the 400-pps but not the 100-pps RDL, and these two correlations differed significantly from each other. Similarly, the across-electrode correlation between GDT and the 400-pps RDL was marginally significant, whereas there was no correlation between GDT and the 100-pps RDL. These findings are consistent with the deterioration in high-rate temporal processing sharing a common basis with the mechanisms involved in gap detection, but not with the limitations in low-rate temporal processing. We will also report the results of a second experiment that measured rate discrimination and pitch ranking at low and high rates, both on the same day that patients’ implants were activated and after two months of listening experience.