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Stress is a linguistic property of a word that specifies which syllable in the word is stronger than any of the others. Early studies such as Fry (1955, 1958), Lieberman (1960), Beckman (1986), Harrington, Beckman, and Palethorpe (1998) (see also Laver, 1994 for an overview) have shown that there are clear acoustic differences between stressed and unstressed syllables: stressed syllables are realized with higher pitch, higher intensity, longer duration, and more peripheral vowel quality than unstressed syllables. Studies in many stress-accent languages show that the stressed realization of a syllable differs from the unstressed realization of the same syllable by having higher pitch. Also, results have showed that speakers consistently use duration to distinguish between open and central vowels that contrasted in stress at the word level. In contrast with F0 and duration, the relation of intensity variation in the speech signal to word stress is still controversial. In this paper, we investigated the role of acoustic factors involved in perceptually differentiating simple past from present perfect verbs in Persian, through manipulation of fundamental frequency (F0) and duration. Thus, tokens were resynthesized from the phonetic forms of Persian simple past and present perfect verbs in which F0 and duration were manipulated in several steps. The target tokens were presented to some native Persian participants to identify as simple past or present perfect. Results suggested that Persian listeners’ judgements of the tense of the target tokens depend, to a great extent, on the local F0 values of the verbs’ syllables as any amount of increase in the local F0 points of the respective syllables can categorically change the listeners’ judgements about the temporal reading of the verbs involved. On the other hand, results for duration showed that values of this parameter fail to produce a significant effect on listeners’ judgements. [ABSTRACT FROM AUTHOR]

This paper addressed the acoustic factors involved in distinguishing simple past and present perfect tenses in Persian. The pronunciation of Persian simple past and present perfect tenses in colloquial speech are the same segmentally but different in terms of the position of stress. In an experimental study, the pattern of distribution of some important prosodic parameters, including F0, intensity, and duration, was investigated in a speech corpus consisting of 24 sentences. Results suggested that none of the study parameters could differentiate simple past and present perfect tenses reliably and consistently. After normalizing F0 and computing the average pitch for all acoustic data per speaker, it was found that it is the value of F0 peaks and valleys in the target syllables that makes a fundamental distinction between simple past and present perfect. Results of statistical tests confirmed this finding, suggesting that the local F0 value is a reliable and consistent parameter that distinguishes simple past from present perfect in both the syntagmatic and paradigmatic axes. [ABSTRACT FROM AUTHOR]