Thai English foreign language learners' discrimination of voicing contrast in English obstruents

The purpose of this study was to investigate common difficulties among Thai students in perceiving English voiced and voiceless stops, fricatives and affricates. The study specifically tested sixteen sounds: /p/,/t/,/k/,/b/,/d/,/g/,/f/,/v/,//,//, /s/, /z/,
Two hundred students purposively selected from Mattayomseuksa 3 (M3) and 6 (M6) at Amnatcharoen School (107 M3, and 93 M6 students, respectively). The participants took a discrimination test consisting of sixteen English obstruents formed as 24 stimulus pairs. There variables under investigation were: syllabic position (onset, intervocalic, and coda), manner of articulation (stops, fricatives and affricates) ang status in the Thai phonetic repertoire (present and absent).
The results of the experiment show little difference between the discrimination ability of the two groups of participants. The findings support and challenge the Speech Learning Model proposed by Flege (1995) while supporting the Critical Period Hypothesis (Lenneberg, 1967).