Analysis of Relationship between Duration Characteristics and Subjective Evaluation of English Speech by Japanese learners with regard to Contrast of the Stressed to the Unstressed

To improve more effectively the learners’ proficiency to control contrast of the stressed to the unstressed in English teaching, it is necessary to analyze how the acoustical characteristics of learners' speech are related to the perceptual evaluation by teachers. This paper analyzes A) learner characteristics of durations measured in speech units related to stress, which are stressed and unstressed syllables, and strong and weak vowels, and B) the relationship between the duration characteristics and subjective evaluation of English rhythm control proficiency. As a result of analyses, the following were revealed. Duration characteristics of learner speech were as follows: 1) Lengthened duration of speech units and inserted pauses make learners’ sentence duration longer compared to that of native speakers. 2) Learner speech does not provide sufficient contrast between the stressed and the unstressed as native speech does, because it is difficult for learners to shorten the durations of unstressed syllables and weak vowels. The relationship between the duration characteristics and subjective evaluation were as follows: 1) Duration of the syllable, especially the unstressed syllable, and that of the vowel, especially the weak vowel, have a stronger correlation with subjective evaluation score. 2) Shorter duration of the weak vowel rather than that of the unstressed syllable tend to be evaluated as more native-like speech, that is, shortening the duration of the weak vowel strongly affects subjective evaluation.