To examine the effect of mora duration by the context within a word,
we measured the length of consonant and vowel sounds using the
CV-C samples which were all chosen from the first mora position
of four mora words on the condition that V was /a/.
Figure 5.5 shows their distributions in a CV
coordinate system. It was found that on the whole the mora CV
whose C belonged to the same for manner of articulation lay in
specific region (the circle) only if the following consonants were
also the same for manner of articulation, i.e., mora duration is
mainly affected by the manner of articulation of the preceding and
following consonants and at that time vowel length is adjusted as much
as possible within the limits of its inherent duration to compensate
for the duration of tautomoraic segments[40]. The number of
these CV-C context was not so enough, but the mora
hypothesis was a little shown because the mora CV regions were
similarly formed in the same direction
. Besides, mora duration is also divided by the presence or absence of voicing of following consonants
(the dotted line), i.e., vowels are generally longer before voiceless
consonants than before voiced consonants in
Japanese[41][42]. It was also found that the
manner of articulation correlated well with the vowel
duration[39]. Jesperson (1967) suggested that the
duration of a vowel is function of its articulatory distance to the
adjacent consonants[42].
図 5.2: Decrease of mora length in proportion to number of mora
図 5.3: Lengthening and shortening in mora position of two, three,
four, and five mora words
図 5.4: Means and standard deviations of duration for Japanese vowels and consonants
図 5.5: Effect of context within CV mora and across
V-C mora boundary in a CV coordinate system
But we could not find any cues about it. From the experiment, we have found that mora duration varies by three kinds of factors as a rule : (1) shortening in inverse proportion to the length of a mora count, (2) word initial shortening, word final lengthening, (3) mora is generally longer before voiceless consonants than before voiced consonants.
| SOFT | HARD | MANNER OF | PHONEMES | |
| TEMP. | TEMP. | ARTICULATION | ||
| VP | Voiced Plosive | /b/,d/,/g/ | ||
| VF | Voiced Fricative | /z/,/j/ | ||
| V | NA | Nasal | /m/,/n/ | |
| AP | Approximant | /w/,/y/ | ||
| TF | Tap or Flap | /r/ | ||
| UP | Unvoiced Plosive | /p/,/t/,/k/ | ||
| U | UF | Unvoiced Fricative | /f/,/s/,/sh/,/h/ | |
| AF | Affricate | /ch/,/ts/ |
