Japanese learners of American English (AE) can face difficulties producing mid and low AE vowels /æ/, /^/, and /ɔ/, which tend to be perceptually assimilated into native vowel categories. An interactive multimedia visualization of the acoustic-phonetic vowel space (JSpace) was provided to assist Japanese learners of English as a foreign language (EFL), allowing students practice finding and auditing AE vowel sounds in an acoustic space calibrated with reference Japanese vowels. In each training session, students explored a set of seven AE vowel sounds: /æ/-/^/-/ɔ/-/ɪ/-/ɛ/-/u/-/U/. Clicking in the acoustic space generated a vowel sound synthesized using the corresponding first and second formant frequencies. Participants were 28 first-year Japanese undergraduates at a private university in Tokyo who received four weeks of targeted training via the JSpace interactive visualization, during which training their formant frequency settings for the seven AE vowel sounds were tabulated for analysis. From the first to the fourth week, there was a substantial reduction in the spread of first-formant frequencies for just three of the seven AE vowels: /ɪ/, /æ/, /^/. Performance on a forced-choice, minimal-pairs discrimination task was improved from pre-training to post-training assessments.
Martens et al. (2025) studied this question.