Discussion
Benefit of periodicity enhancement for pitch-related tasks The present study showed that CI users’ ability to perceive tone contrasts was reduced when speech was mixed with noise. This finding is consistent with results reported by previous studies on Mandarin tone recognition on normal-hearing listeners listening with CI simulation (Kong & Zeng, 2006), and on real CI users (Milczynski et al, 2012). The diminished temporal pitch performance could be the result of the reduction of modulation depth caused by the noise and the random jitters from noise envelope. Previous studies have shown the effect of modulation depth on temporal pitch perception. Geurts and Wouters (2001) reported that CI users’ ability to discriminate pitch of amplitude-modulated stimuli decreased with decreasing modulation depth. In one extreme, when modulation depth was too small to be detected, the perceived pitch would correspond to that produced by pulse-train carrier instead of that produced by the rate of modulation (McKay et al, 1995), or if the carrier rate was too high, it would be out of the temporal pitch range for CI users.