Effects of Accent and Vowel Context on Thai Learners’ Perception of English Dental Fricatives

Abstract

English dental fricatives /ð/ and /θ/ are known to pose persistent perceptual difficulties for Thai learners of English because these sounds do not exist in the Thai phonological system. In addition, variation in English accents and surrounding phonetic environments may further influence learners’ ability to perceive and distinguish these consonants accurately. This study investigates how Thai learners perceive the English dental fricatives /ð/ and /θ/ across different English accents and vowel contexts. Thai participants listened to English words containing the sounds /f, θ, ð, t, d/ in word-initial position. After hearing each stimulus, they identified the sound they perceived and rated its similarity using a goodness rating scale. The results show that Thai learners identified some English accent varieties, particulary the American accent, more accurately than others. Accent significantly influenced the identification of /ð/ across all vowel contexts, while vowel context affected the perception of /θ/ only in the low and high vowel contexts. However, accent did not have a significant effect on the identification of /θ/ in the back vowel context. Additional analyses revealed that learners frequently assimilated /ð/ to the English categories /ð/ and /d/, whereas /θ/ was often perceived as /f/ or /t/. The goodness rating and identification results showed that learners could generally distinguish all target contrasts in the American and Philippine accents. However, difficulties were observed for the /d–ð/ contrast in the British, Indian, and Thai accents, particularly across high and back vowel contexts. Learners also had difficulty distinguishing the /t–θ/ contrast in the Indian and Thai accents in several vowel contexts. Overall, the findings highlight the influence of accent variation and phonetic context on Thai learners’ perception of English dental fricatives. These findings suggest that exposure to diverse English accents and phonetic contexts may play an important role in improving Thai learners’ perception of English dental fricatives.