The present dissertation investigates the perception of L2 English vowels by L1 Arabic subjects representing two Arabic dialects, Saudi Arabic (SA) and Tunisian Arabic (TA). The aim is to see whether L1 cross-dialectal differences in sounds influence the perception process for L2 sounds. The focus was on advanced learners, who learned L2 English in their native countries, and were examined on the perception of L2 English vowel contrasts /i/~/I/, /u/~/upsilon/, and /ae/~/"special character omitted"/. The dissertation provides an empirical investigation regarding the role of native language speech varieties on L2 phonological acquisition.

To explore the role of L1 dialect background on L2 vowel perception, there was a need to conduct two experiments. The first one was to collect baseline acoustic measurements for vowels in both investigated languages, in English language by native speaker of American English (AE), and in Arabic language by native speakers from both dialect groups (SA & TA). These have helped to have a detailed acoustic comparison for vowels. The second, main experiment included a perceptual AX discrimination task, where advanced L2 learners from both dialect groups had to contrast on the target L2 vowels.

In both experiments, the obtained data received full analysis that included spectrographic analysis and employing descriptive statistics, specifically a series of One-Way ANOVA test. The findings in the first experiment reveal significant differences in vowel acoustic characteristics cross-dialectally, which suggests that it could have a reflected effect on listeners' perception of L2 vowels and indeed there was. The reported results in the second experiment substantiate the stated hypothesis in this dissertation, that L1 Arabic cross-dialectical specific phonetic vowel variation between SA and TA would lead to variation in L2 vowel perception. This dissertation's results underscore the central role of L1 variety in shaping the perception of L2 sound, and that it is crucial for future L2 phonological research to consider such factors in their investigation.