| In this study, three acoustic correlates--fundamental frequency, syllable duration and intensity--are examined with respect to four sentence stress conditions and their relationship to perceived focus. It is found that when a syllable is stressed, its pitch range expands dramatically followed by an immediate fall of F0 excursion. Usually, the duration of the stressed syllable also becomes longer. However, intensity is generally not related to stress.;When a syllable is stressed for narrow focus, the post-stress dropping of the F0 excursion sometimes fails to override the inherent rising tone of the following syllable. This is found to be largely related to the tone of the preceding stressed syllable and the reduction of the top line of the post-stress syllable.;This study also uses multiple regression models to examine the correlations between perceptual scores of focus and various measurement points of acoustic parameters. The results clearly indicate that F0 is, by far, the most important acoustic parameter for stress. When a syllable is stressed, the pitch range of the stressed syllable is always selected first by the regression procedure. In most cases, the top line of the post-stress syllable is also found to be crucial. Syllable duration appears to be the next important after F0. However, intensity is generally not significant for indicating sentence stress. In many cases, the parameter is simply dropped by the regression model.;This study also finds that broad focus and one of the narrow focus conditions in which the last word is stressed are closely related. Perceptually, the two categories are hard to distinguish. In both cases, the overall F0 excursion is high and flat. However, the acoustic analysis shows a slight difference. Under narrow focus, the final word is more prominent, while under broad focus, the pitch range for the sentence initial word is slightly greater. It is suggested that, under broad focus, stress falls on two places. Primary stress falls on the last word, whereas the secondary stress falls on the first one. |
