Relationships Between Acoustic Characteristics and Intelligibility Scores: A Reanalysis of Japanese Speakers' Productions of American English Liquids.

The primary purpose of this research report was to investigate the relationships between acoustic characteristics and perceived intelligibility for native Japanese speakers' productions of American English liquids. This report was based on a reanalysis of intelligibility scores and acoustic analyses that were reported in two previous studies. We examined which acoustic parameters were associated with higher perceived intelligibility scores for their productions of /l/ and /ɹ/ in American English, and whether Japanese speakers' productions of the two liquids were acoustically differentiated from each other. Results demonstrated that the second formant (F2) was strongly correlated with the perceived intelligibility scores for the Japanese adults' productions. Results also demonstrated that the Japanese adults' and children's productions of /l/ and /ɹ/ were indeed differentiated by some acoustic parameters including the third formant (F3). In addition, some changes occurred in the Japanese children's productions over the course of 1 year. Overall, the present report shows that Japanese speakers of American English may be making a distinction between /l/ and /ɹ/ in production, although the distinctions are made in a different way compared with native English speakers' productions. These findings have implications for setting realistic goals for improving intelligibility of English /l/ and /ɹ/ for Japanese speakers, as well as theoretical advancement of second-language speech learning.