Acoustic Analysis of advanced and intermediate Persian EFL Learners' Pronunciation of English Vowels

This paper reports the results of an experimental study on non-native production of english vowels. two groups of persian efl learners varying in language proficiency were tested on their ability to produce the nine plain vowels of american english. vowel production accuracy was assessed bymeans of acoustic measurements. ladefoged and maddison’s (1996) f1´f2 measurements for american english vowel space were used as reference values to be compared with the measurements obtained from the production of persian efl learners. the acoustic measurements revealed that learners were not able to control acoustic parameters of vowel quality, even for the more similar vowels in the two languages, in a native-like manner due to interference from their native vowel system. spectral accuracy measures also did not progress toward more native-like values in the productions of the more proficient learners. interestingly, the positions achieved for the more dissimilar vowels were neither close to their closest l1 counterparts nor close to their native categories. interpreting this latter result within the perceptual assimilation model proposed by best (1994), it could be stated that learners established new phonetic categories for the vowel contraststhat were not used in their native phonological system.