A Phonetic Study of Vowel Reduction in Persian

This paper studies the phonetic aspects of vowel reduction in Persian. Vowel reduction was examined in unstressed syllables using duration and F1 and F2 spectral values across different consonantal contexts. Results showed a strong effect of stress on duration across all consonantal contexts, but the results for F1 and F2 frequencies varied with vowel type as well as consonantal context. Most vowels had non-significant formant changes in unstressed condition as compared to stressed condition; however, the vowel /a/ had significant spatial reduction in the direction of the center of the vowel space. The results support neither of the two known articulatory hypotheses concerning vowel reduction, namely, centralization (in unstressed position) by target undershoot, and reduction due to co-articulation with the consonant context. Instead, the results lend support to the dispersion theory of speech perception which argues that vowel systems cross languages tend to utilize the available acoustic vowel space so that maximal auditory contrast is maintained. It is further argued that the position of vowels in the acoustic vowel space is influenced by this dynamical repelling force which has come to be called adaptive dispersion.