Cantonese lexical tone recognition from frequency-specific temporal envelope and periodicity components in the same...

Temporal envelope and periodicity components (TEPCs) in the speech signal offer important cues for speech recognition. A recent study revealed that TEPCs extracted from the high-frequency regions contribute significantly to Cantonese lexical tone recognition at the monosyllabic word level (Yuen et al., 2006). The aim of the current study was to compare the contributions of TEPCs from different frequency regions for Cantonese lexical tone recognition in connected speech, using the same or different noise band carriers and a very limited number of frequency bands. Test stimuli were Cantonese disyllabic word minimal pairs differing from each other only in lexical tone. The test stimuli set exhausted all possible 15 lexical tone-pair contrasts (six lexical tones in total) for the first and the second syllables. The TEPC of the test items were extracted by full-wave rectification and low-pass filtering and were used to modulate a speech-spectrum-shaped noise carrier to create the test stimuli. The stimuli therefore contain only TEPCs but no fine structure components (FSCs) of the original signal. Multiple sets of stimuli were created with different combinations of TEPC-modulated frequency bands. Twenty normal-hearing subjects participated in the study. Even in a single-band condition, much robust lexical tone recognition was obtained with TEPC provided from the high-frequency region than those from the low frequency region. This high frequency region TEPC advantage was consistent using noise band carriers from different frequency regions. The TEPCs in the high-frequency region are more important for Cantonese lexical tone recognition, when FSCs are not available. The results indicate a potential to improve speech recognition in tonal languages by preserving or enhancing the critical TEPCs via new signal-processing algorithms in hearing prosthesis.