Spectral and temporal implementation of Japanese speakers’ English vowel categories: A corpus-based study

Abstract

This study investigates the predictions of second language (L2) acquisition models — SLM, PAM-L2, and L2LP — on how native (L1) Japanese speakers implement the spectral and temporal aspects of L2 American English vowel categories. Data were obtained from 102 L1 Japanese speakers in the J-AESOP corpus, which also includes nativelikeness judgments by trained phoneticians. Spectrally, speakers judged to be less nativelike showed a strong influence of L1-L2 category assimilation, except L2 /æː/ whose dissimilarity from L1 categories likely triggered new category formation, in accordance with SLM and PAM-L2. However, more nativelike speakers showed vowel spectra similar to those of native English speakers for all vowels, which aligns better with L2LP. Temporally, although speakers tended to assimilate the phonetic length of English vowels to Japanese phonemic length distinctions, segment-level L1-L2 category similarity was not a significant predictor of the speakers’ nativelikeness. Instead, implementation of prosodic-level factors such as stress and phrase-final lengthening were better predictors. The results highlight the importance of suprasegmental factors in successful L2 category learning and also reveal a weakness in current models of L2 acquisition, which focus primarily on the segmental level. The use of speech corpora for L2 research is discussed.