For the words of twenty native speakers, we measured their average mora duration on the basis of the number of mora. For reference, the sample number of two mora words is 56, three mora words 217, four mora words 222, five mora words 22, six mora words 3, respectively. Six mora words were excluded in the measurement. Figure 5.2 shows the average mora duration to be shorter as the number of mora increases[38]. It is also clear that all speakers have quite similar tendencies in their shortening[37]. Figure 5.3 shows the lengthened or shortened mora duration in their respective mora positions. It is noteworthy that the average length of a second mora of two mora words is longer than that of the first one for all of the native speakers (top left). The speakers also showed a regularity of their mora rhythm patterns for other n-mora words.
