Identification training adapted to the learner’s vowel space aids in improving native Japanese speakers’ pronunciation of American English vowels

Native speakers of Japanese learning English as a foreign language often have difficulty pronouncing certain American English (AE) vowels, such as the mid vowels /ae/, /ɑ/, / ^/, /ɔ/, and /ɚ/, which typically are assimilated to native vowel categories. It was shown that vowel identification training which was adapted to the learner’s vowel space could aid in improving the native Japanese speakers’ pronunciation of a set of 12 AE vowels that included the 5 more difficult mid vowels. Estimates of the vocal-tract length (VTL) for 53 learners were based upon the central tendency and range of the four lowest formant frequencies observed in their recordings of five short statements in the Japanese language. Having thus characterized the individual vowel spaces of 53 learners, 33 were placed in a “longer-VTL” group while the remaining 20 were placed in a “shorter-VTL” group. Those in the “longer-VTL” group were given periodic identification training using examples of 12 American English monophthongs in a consonant-vowel-consonant (CVC) context that sounded as if a male AE speaker with similar VTL had uttered them. The “shorter-VTL” learners heard training examples that sounded as if the CVCs were uttered by a female AE speaker with similarly short VTL.