Enhancing the temporal fine structure with the temporal limits encoder for cochlear implants: Effects on pitch discrimination

Abstract

To enhance the mostly discarded temporal fine structure in modern cochlear implant (CI) strategies, a temporal-limits-encoder (TLE) strategy was proposed by downshifting the high-frequency-band-limited signal to a low-frequency-temporal-pitch-limits range of CIs [Meng et al., J. Acoust. Soc. Am.(2016)]. This study investigates pitch perception with a TLE strategy compared with a standard advanced combinational encoder (ACE) strategy. Seven CI subjects were tested in a complex-tone-pitch discrimination task measuring the fundamental frequency difference limens (F0DLs) at four reference F0s (250, 313, 1000, and 1063 Hz, which are the center and upper cross-over frequencies of two bands). Results show that (1) the CI listeners generally had lower F0DLs with TLE than with ACE (group mean F0DL benefits of TLE over ACE of 5.0, 9.6, 0.5 and 4.3 percentage points at the four reference F0s, respectively) and (2) the two strategies had comparable sentence recognition performance in both quiet and noisy conditions. These findings suggest that the slowly varying TFS introduced by TLE is feasible in pitch discrimination for CI listeners and is not significantly detrimental to sentence recognition. This discrimination advantage can be explained by larger differences in the temporal fluctuations on individual channels with TLE than with ACE.