It about investigates how vowel duration and vowel quality affect degrees of vowel-to-vowel. The effects of these two factors on vowel-to-vowel articulation. Phonological duration differences due to vowel length distinction were examined in Thai. it was hypothesized that shorter vowel durational could result in more vowel-to-vowel articulation. thus the susceptibility of different vowel quality to vowel-to-vowel coarticulation