Phonetic research on stress has shown that fundamental frequency and duration are effective acoustic correlates of stress in many languages (e.g., Fry, 1955; see Lehiste, 1970; and Cooper and Sorensen, 1981). Thus, we expect stressed syllables to have higher FO and longer durations than unstressed syllables, other factors being equal. In addition to these effects, stress has been shown to affect formant values in vowels. For example, formants in unstressed vowels may centralize, becoming more schwa-like (Lindblom, 1963). Therefore, stress, or rather lack of stress, may sometimes alter the acoustic characteristics of phonemes to the point of neutralization. While substantial data exist documenting the effects of stress on segments and syllables, there has been less investigation of stress in lexical tones. In particular, there is little published data examining the effectiveness of FO and duration as correlates of stress for tones. Moreover, it is not clear how stress-altered FO patterns may affect tones, which critically depend upon FO for phonemic contrasts. For instance, it is conceivable that changes in FO due to lack of stress may neutralize the distinctive contour of a tone, similar to the case of centralized formants in unstressed vowels. To examine the effects of stress on tones, the current study reports data on stress in Mandarin Chinese. In Mandarin, four tones serve to distinguish all lexical items except a small number of atonic syllables. Syllables with tones may have primary, secondary and lower degrees of stress, while atonic syllables are always unstressed. This study presents evidence in two areas. First, the investigation provides data on the acoustic correlates of stress in Mandarin tones. Second, the study considers whether FO contours of unstressed tones reduce or neutralize completely, resulting in tonelessness.

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