Lexical tone recognition with spectrally mismatched envelopes.

It has been shown that frequency-place mismatch has detrimental effects on English speech recognition. The present study investigated the effects of mismatched spectral distribution of envelopes on Mandarin Chinese tone recognition using a noise-excited vocoder. In Experiment 1, speech samples were processed to simulate a cochlear implant with various insertion depths. The carrier bands were shifted basally relative to the analysis bands by 1-7 mm in the cochlea. Nine normal-hearing Mandarin Chinese listeners participated in this experiment. Basal shift of the carriers only slightly affected tone recognition. The resistance of tone recognition to spectral shift can be attributed to the overall amplitude contour cues that are independent from spectral manipulations. Experiment 2 examined the effects of frequency compression, where widened analysis bands by 2, 6, and 10 mm were compressively allocated to narrower carrier bands. Five of the 9 subjects participated in Experiment 2. It appears that the expanded frequency information especially on the low frequency end can compensate for the distortion from frequency compression. Thus, spectral shift might not pose a severe problem for tone recognition, and allocation of wider frequency range to include more low frequency information might be beneficial for tone recognition.