[Contrast between vowel formants affects impressions of the speaker's personality and speech style].

This study investigated the relationship between the distinctness of vowels in speech and impressions of the speaker's personality and speech style. Vowel sounds are considered to carry mainly phonetic information. For the experiment, formant frequencies of vowel sounds in original speech were altered to synthesize speech stimuli into four levels of formant contrast among different vowels. In Experiment 1, 36 university students listened to the speech stimuli and evaluated the speaker's personality using the Big Five scale. In Experiment 2, 35 participants evaluated the speech style. As the phonetic contrast between vowels became bigger, the trait evaluations of "conscientiousness" showed an asymptotic increase. "Agreeableness" was evaluated as high when the vowel contrast was somewhat bigger than the original before beginning to decrease. Regarding speech styles, "naturalness" and "fluency" were evaluated highest when vowel contrasts were somewhat bigger. "Pleasantness" was evaluated equally high for original and somewhat big contrasts, but lowest for the smallest contrast. In conclusion, vowel distinctness conveys not only phonetic information but also contributes to impressions of speech style and the speaker's personality systematically.