Speaker normalization in the perception of Mandarin Chinese tones

This study investigated speaker normalization in perception of Mandarin tone 2 (midrising) and tone 3 (low-falling-rising) by examining listeners' use of F0 range as a cue to speaker identity. Two speakers were selected such that tone 2 of the low-pitched speaker and tone 3 of the high-pitched speaker occurred at equivalent F0 heights. Production and perception experiments determined that turning point (or inflection point of the tone), and delta F0 (the difference in FO between onset and turning point) distinguished the two tones. Three tone continua varying in either turning point, delta FO, or both acoustic dimensions, were then appended to a natural precursor phrase from each of the two speakers. Results showed identification shifts such that identical stimuli were identified as low tones for the high precursor condition, but as high tones for the low precursor condition. Stimuli varying in turning point showed no significant shift, suggesting that listeners normalize only when the precursor varies in the same dimension as the stimuli. The magnitude of the shift was greater for stimuli varying only in delta FO, as compared to stimuli varying in both turning point and delta FO, indicating that normalization effects are reduced for stimuli more closely matching natural speech.