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Duration Differences.

Appendix 3 shows mean acoustic vowel durations for each vowel phoneme, for stressed and unstressed vowels, and for vowels before and after voiced and voiceless consonants, for each speaker. Standard deviations and standard errors are also given there. Note that the means given there are grand means; some of them may be skewed by uncontrolled interactions with other effects. Many interactions will be washed out by the law of large numbers, but perhaps not all, so some caution must be used in interpreting the numbers. Table [*] was constructed from the data in Appendix 3. For each short/long pair (that is, /i, ii/, /e, ie/, /a, aa/, /o, uo/, /u, uu/), the mean vowel durations are presented, and the ratio of the mean durations of short and long vowels is expressed as a percentage. The mean durations for all short vowels together and all long vowels together (including diphthongs, in this case) are also given, along with the corresponding ratio.

Diphthongs (/ai/, /ou/, etc.) are included in ``all'' long vowels.

Table: Jamaican mean vowel durations (ms) and short/long duration ratios (percent).
Juba Roasta
V: V Ratio V: V Ratio
/i:/ 116 /i/ 54 47% /i:/ 96 /i/ 54 56%
/e:/ 135 /e/ 83 61% /e:/ 96 /e/ 63 66%
/a:/ 190 /a/ 87 46% /a:/ 150 /a/ 81 54%
/o:/ 122 /o/ 91 75% /o:/ 102 /o/ 63 62%
/u:/ 133 /u/ 58 44% /u:/ 108 /u/ 57 53%
all 144 all 76 52% all 125 all 64 51%

For the two Jamaican speakers studied, phonological vowel length (including diphthongs as long vowels) approximately doubles the vowel duration in the aggregate (64:125ms for Roasta, 76:144ms for Juba). Roasta generally spoke more rapidly than Juba, which accounts for the generally lower segmental durations measured for his speech.

If slower speech enables underlying durational patterns to manifest more clearly, then this would account for the smaller ratios (= greater differences) between Juba's long and short vowels than between Roasta's long and short vowels.

The details of the long/short relationship differ in interesting ways for different vowels. In particular, the mid vowels stand out from the others, for both speakers, as seen in the ratios of mean durations in Table [*], expressed as percentages. These ratios are among the main phonetic effects of phonological vowel length. If average duration of acoustic vowels corresponding to a long vowel were twice the average duration of acoustic vowels corresponding to short vowels, then this ratio would be 50%. Here we see that the high and low vowels have similar ratios for each speaker, while the mid vowels have considerably higher ratios. That is, the durational difference between long and short vowels is relatively smaller for the mid vowels, because the ratios are closer to 1, or 100%.

Why should phonological length correspond to a smaller difference for mid vowels than for high and low vowels? The long mid vowels are phonologically special in the Jamaican vowel system: their nuclei are raised (when stressed) and they become phonetically gliding vowels, so that duration and peripherality are not the only phonetic features distinguishing them from the corresponding short vowels. The high and low long vowels, on the other hand, do not become glides; they largely remain monophthongs even when stressed.

These facts may be related. That is, the special status of the mid vowels would seem to be related to their distinctive patterning with respect to acoustic vowel duration. It is tempting to speculate that the phonetic process by which the vowel becomes a glide has a weakening effect on the durational difference between the long and short vowels. This hypothesis is supported by the fact that in the other dialects studied, the long vowels generally have phonetic glides, and furthermore phonological vowel length corresponds to a smaller difference between the vowel durations. Thus, the ratios between the average short vowel duration and the average long vowel duration for the other speakers studied are 90/126ms=71% (Judy, Chicago), 81/109ms=74% (Jim, Chicago), 91/107ms=85% (Rita, Chicago), 105/148ms=71% (James H., Alabama), and 79/102ms=77% (Vince, L.A. Chicano). These ratios for Juba and Roasta are 52% and 51% (including diphthongs), showing a much greater difference in phonetic duration, corresponding to phonological vowel length in Jamaican Creole.

Thus there may be a general association of phonetic gliding of long vowels with a weakening of the durational differences between the corresponding long and short vowels. Long vowels, which have phonetic glides in the other dialects, are phonetically not as much longer than the corresponding short vowels. The long vowels that in Jamaican have phonetic glides are also not as much longer, compared with the long monophthongs.

Whether or not this general association between phonetic gliding of long vowels and a relatively difference between the durations of long and short vowels is born out in later studies, it is clear that phonological vowel length and gliding in Jamaican Creole is realized by very large durational differences, with ratios in the neighborhood of 1:2.

next up previous
Next: Phonological Length and Vowel Up: Acoustic Correlates of Phonological Previous: Acoustic Correlates of Phonological
Thomas Veatch 2005-01-25