Cantonese tone recognition with enhanced temporal periodicity cues

This study investigated the contributions of temporal periodicity cues and the effectiveness of enhancing these cues for Cantonese tone recognition in noise. A multichannel noise-excited vocoder was used to simulate speech processing in cochlear implants. Ten normal-hearing listeners were tested. Temporal envelope and periodicity cues (TEPCs) below 500 Hz were extracted from four frequency bands: 60-500, 500-1000, 1000-2000, and 2000-4000 Hz. The test stimuli were obtained by combining TEPC-modulated noise signals from individual bands. For periodicity enhancement, temporal fluctuations in the range 20-500 Hz were replaced by a sinusoid with frequency equal to the fundamental frequency of original speech. Tone identification experiments were carried out using disyllabic word carriers. Results showed that TEPCs from the two high-frequency bands were more important for tone identification than TEPCs from the low-frequency bands. The use of periodicity-enhanced TEPCs led to consistent improvement of tone identification accuracy. The improvement was more significant at low signal-to-noise ratios, and more noticeable for female than for male voices. Analysis of error distributions showed that the enhancement method reduced tone identification errors and did not show any negative effect on the recognition of segmental structures.