Multi-channel cochlear implant patients with different open speech understanding show some similar basic psychophysical results.

A series of tests was recently undertaken on three multi-channel cochlear implant patients showing different degrees of open speech understanding in order to try to determine underlying differences in inner ear excitation. First we wanted to determine whether these patients showed notable differences in basic psychophysical tasks. This article reports a series of measures including absolute and differential thresholds, simultaneous and forward masking, and some polarity and phase perception. Absolute and differential sensitivities were found to be similar. In forward or simultaneous masking, the patients often showed no masking at all and in cases of masking, no frequency selectivity. In forward masking, their time constants were found to be longer than those in normal hearing. Multi-harmonic signals differing only in phase relations to produce large differences in peak amplitude did not seem to elicit different perceptions. In stimulating with very low-frequency square waves, only negative going fronts were perceived. The similarity of results for the 3 patients in this study suggest that individual differences lie in more complex stimulus processing and perhaps in qualitative aspects of perception.