Temporal and spectral cues in Mandarin tone recognition.

This study evaluates the relative contributions of envelope and fine structure cues in both temporal and spectral domains to Mandarin tone recognition in quiet and in noise. Four sets of stimuli were created. Noise-excited vocoder speech was used to evaluate the temporal envelope. Frequency modulation was then added to evaluate the temporal fine structure. Whispered speech was used to evaluate the spectral envelope. Finally, equal-amplitude harmonics were used to evaluate the spectral fine structure. Results showed that normal-hearing listeners achieved nearly perfect tone recognition with either spectral or temporal fine structure in quiet, but only 70%-80% correct with the envelope cues. With the temporal envelope, 32 spectral bands were needed to achieve performance similar to that obtained with the original stimuli, but only four bands were necessary with the additional temporal fine structure. Envelope cues were more susceptible to noise than fine structure cues, with the envelope cues producing significantly lower performance in noise. These findings suggest that tonal pattern recognition is a robust process that can make use of both spectral and temporal cues. Unlike speech recognition, the fine structure is more important than the envelope for tone recognition in both temporal and spectral domains, particularly in noise.