The effect of F0 contour on the intelligibility of speech in the presence of interfering sounds for Mandarin Chinese.

In Mandarin Chinese, the fundamental frequency (F0) contour defines lexical "Tones" that differ in meaning despite being phonetically identical. Flattening the F0 contour impairs the intelligibility of Mandarin Chinese in background sounds. This might occur because the flattening introduces misleading lexical information. To avoid this effect, two types of speech were used: single-Tone speech contained Tones 1 and 0 only, which have a flat F0 contour; multi-Tone speech contained all Tones and had a varying F0 contour. The intelligibility of speech in steady noise was slightly better for single-Tone speech than for multi-Tone speech. The intelligibility of speech in a two-talker masker, with the difference in mean F0 between the target and masker matched across conditions, was worse for the multi-Tone target in the multi-Tone masker than for any other combination of target and masker, probably because informational masking was maximal for this combination. The introduction of a perceived spatial separation between the target and masker, via the precedence effect, led to better performance for all target-masker combinations, especially the multi-Tone target in the multi-Tone masker. In summary, a flat F0 contour does not reduce the intelligibility of Mandarin Chinese when the introduction of misleading lexical cues is avoided.