ATR Human Information Process. Res. Labs., 2-2 Hikaridai Seika-cho, Soraku-gun, Kyoto, 619-02 Japan
In order to estimate the processing unit of Japanese speech production, the influence of the number of syllables and morae on reaction time (RT) in speech production was analyzed. In experiment 1, RT was measured for one- to four-mora nonwords consisting only of Japanese CV syllables [ka] or [ta]. Five subjects produced stimulus words as soon as possible after the visual onset signal was presented. RT was defined as the duration from the moment of onset signal presentation to the release of word-initial plosive consonant. Results showed a tendency for RT to increase as the number of CV syllables increases. In experiment 2, stimulus words consisted of CV syllables and vowels without a syllable-initial consonant, or CV syllables and nasal sounds [N] without a syllable-final vowel. Note that, in Japanese, a vowel and nasal sound [N] can be a mora like a CV syllable. For these stimuli, the RT was not influenced by the increase of the number of morae. These results suggests a possibility that a mora consisting of a CV syllable is the smallest segment of the processing unit in Japanese speech production. However, morae consisting of a single vowel or nasal sound cannot perform as independent processing units.