The Intelligibility of Thai-Accented English Pronunciation to Native and Non-Native Speakers of English

World Englishes (Kachru, 1985) and English as an International Language (EIL) are grounded in the concept of multiplicity. Such proliferation of non-native varieties of English leads to several controversies including the intelligibility of its speakers. Although the concerns have been continuously addressed in EIL research, the focus was mainly toward major ESL accents. Thai English language educators know very little about the scenario of Thai English in relation to its use in international settings. This study explored the macro-sociolinguistic characteristics of Thai English of which the underlying investigation: what level of Thai accentedness in English pronunciation can be considered intelligible to international users of English and what pronunciation features instances result in intelligibility failure, was undertaken. Thai-accented English spontaneous speech with different levels of accent was measured for overall intelligibility using a transcription task performed by the listeners from a variety of different L1 backgrounds. Intelligibility level was measured by the accurate transcription of the recorded speech while the errors in transcription were phonetically analysed to ascertain which phonological features of Thai English led to a decrement in intelligibility. With the concept of Lingua Franca Core (LFC) (Jenkins, 2000), these features must be the focus in teaching English for communicative purposes.
Analysis of the results revealed that the interaction between level of accent and intelligibility affected the different L1 groups in a diverse manner, especially non-native speakers. The salient features identified as posing the highest threat to international intelligibility were cluster simplification, consonant devoicing, lack of final consonant released, and fully stressed unstressed vowels. This research also discovered that intelligibility predictors as gained from subjective methods as questionnaires displayed an unstable correlation to the actual intelligibility as measured by the objective tests.