Hypothesis and Materials
Syllables in Standard Thai can be open, closed by an obstruent /p/, /t/, /k/, or ///, or closed by a nasal /m/, /n/, or /N/. Vowel length is contrastive in closed syllables. Therefore, possible syllable types in Thai are CV, CVN, CVVN, CVO, and CVVO (N=/m, n, N/, O=/p, t, k, //). I will refer to syllables closed by an obstruent (CVO and CVVO) as checked syllables, and other syllables (CV, CVN, and CVVN) as non-checked syllables. There are five tones in Thai—High (H), Mid (M), Low (L), Fall (H°L), and Rise (L°H). On non-checked syllables, all five tones can occur. On CVVO, generally, only H°L and L occur, but in rare instances, H can also occur (e.g., nóot ‘note’; khwO!Ot ‘quart’, both English loanwords). On CVO, generally, only H and L occur, but H°L occurs occasionally (e.g., kO$/ ‘then, consequently’) (Gandour 1974, Hudak 1987). This tonal distribution is summarized in (0) (adapted from Gandour 1974).
(0) Tonal distribution in Standard Thai (Gandour 1974):
-
|
H
|
M
|
L
|
H°L
|
L°H
|
CV
|
+
|
+
|
+
|
+
|
+
|
CVN
|
+
|
+
|
+
|
+
|
+
|
CVVN
|
+
|
+
|
+
|
+
|
+
|
CVVO
|
(+)
|
-
|
+
|
+
|
-
|
CVO
|
+
|
-
|
+
|
(+)
|
-
|
(Parentheses indicate rare occurrence.)
Therefore, the distribution of contour tones in Thai is primarily affected by the checked/non-checked distinction, as non-checked syllables can carry both L°H and H°L whether they have a long or a short vowel. But the phonemic status of vowel length is also relevant, since H°L can occur on CVVO, but usually not on CVO.21
Here I focus on the checked/non-checked distinction. The fact that it is L°H, not H°L, that is missing from the tonal inventory of checked syllables indicates that this aspect of the tonal distribution may be durationally based, since pitch rises take longer to implement than pitch falls with equal excursion. The two durational factors here are checked vs. non-checked, and short vs. long vowels: it is well known that in many Sino-Tibetan languages, vowels in checked syllables are considerably shorter than non-checked syllables; and apparently, a phonemic long vowel is longer than a phonemic short vowel. The crucial durational comparisons here are then between CV and CVVO, and between CVN and CVVO. The first member of each pair has the advantage of being non-checked, while the second member has the advantage of having a phonemic long vowel. Given the contour distribution facts, I lay out the hypothesis for Thai as in (0).
(0) Hypothesis (Standard Thai):
Non-checked syllables have a longer sonorous rime duration than checked syllables. In particular, CV>CVVO, CVN>CVVO.
Thai data were collected from two native speakers: YS (male) and VV (female). The word list used in the study is given in (0). For each of the five syllable types—CV, CVVN, CVN, CVVO, CVO, four monosyllabic words were included. All words have the nucleus /a/ and are either Mid-toned or Low-toned. The speakers read each word with eight repetitions.
(0) Thai word list:
-
|
IPA
|
Gloss
|
IPA
|
Gloss
|
CV
|
ba~…
da~…
|
‘shoulder’
‘to curse’
|
pa~…
pÓa~…
|
‘rain forest’
‘to split’
|
CVVN
|
ca…n
cÓa…n
|
‘a plate’
‘fiber residue’
|
cÓa…m
kÓa~…N
|
‘a bowl’
‘a spinning top’
|
CVN
|
sa~n
daN
|
‘to vibrate’
‘loud’
|
tam
tÓam
|
‘to pound’
‘to do’
|
CVVO
|
kÓa~…t
ba~…t
|
‘to be torn’
‘Thai currency’
|
ba~~…p
ha~~…t
|
‘sin’
‘shore, beach’
|
CVO
|
ba~t
ka~t
|
‘ticket, card’
‘to bite’
|
da~p
da~k
|
‘extinguish’
‘to trap’
|
Results
The sonorous rime duration for the five syllable types are plotted in two separate graphs in (0), one for speaker YS, the other for speaker VV. The gray portion in the bars for CVN and CVVN indicates sonorous duration contributed by the nasal coda.
(0) Thai sonorous rime duration (ms):
a. Speaker YS b. Speaker VV
For each speaker, a one-way ANOVA with sonorous rime duration as the dependent variable and syllable type as the independent variable was carried out. Unsurprisingly, the effect is highly significant for both speakers: for YS, F(4, 135)=623.3, p<0.0001; for VV, F(4, 135)=1157.7, p<0.0001. Fisher’s PLSD post-hoc tests show that for both speakers, both CV and CVN have a longer sonorous rime duration than CVVO at the significance level of p<0.0001.
Therefore, the hypotheses in (0) are supported by the phonetic data. Even though there is no vowel length contrast in open syllables in Thai, the vowel in a CV syllable is phonetically long. It is in fact significantly longer than the long vowel in CVVO. Clearly, the use of ‘CV’ to characterize these syllables should be taken as conventional; it is misleading with regard to the actual duration. The fact that CVN has a longer sonorous rime duration than CVVO is largely due to the contribution of the overly long nasal coda. For both speakers, the nasal coda in CVN accounts for more than half of its sonorous rime duration. But vowel shortening in checked syllables may also be relevant, as speaker VV shows such effect: the vowel in CVVO is considerably shorter than the vowel in CVVN (338ms vs. 396ms).
Recall that Thai allows both L°H and H°L to occur on a non-checked syllable even when it has a short vowel and does not allow L°H on a checked syllable even when it has a long vowel. The data show that this tonal distribution pattern corresponds closely with the phonetic pattern: a longer sonorous rime duration allows a more ‘difficult’ contour—L°H—to surface. The direct approach to tonal distribution correctly predicts that this is a possible pattern, and does not predict the opposite pattern, in which L°H can surface on CVVO, but not on CV or CVN.
The traditional positional faithfulness approach cannot rule out the latter pattern in a principled way, because both CVVO and CVN qualify as prominent positions, and there is no a priori reason to rule out the possibility that CVVO is a better contour tone carrier.
The moraic approach also runs into problems here. Given that there is no vowel length contrast in open syllables, there is no structural pressure to posit the vowel in CV to be bimoraic. But one would have to assume that the vowel in CVVO is bimoraic in order to characterize its contrast with CVO. Therefore the implicational hierarchy under a structure-only approach would be that a contour tone is allowed on CVVO before it is allowed on CV. This is in contradiction with the distribution of contour tones in Thai.
In §3.1, I mentioned that Standard Thai is one of the languages that could help determine the range of coefficient a in the definition of CCONTOUR, which is repeated in (0). This is because the strictest a range 1<a< (from (0)) is determined by the comparison between P1=V1R1 and P2=V2R2 where Dur(V1)2), but Dur(V1)+Dur(R1) > Dur(V2)+Dur(R2), and in Standard Thai, this situation is manifested by P1=VN, P2=VVO.
(0) CCONTOUR = aDur(V)+Dur(R)
We can calculate the a range from the data of the two speakers. The relevant duration values for each speaker are given in (0).
(0) Speaker YS: Dur(V1)=160ms, Dur(R1)=424-160=264ms;
Dur(V2)=315ms, Dur(R2)=0.
Speaker VV: Dur(V1)=187ms, Dur(R1)=443-187=256ms;
Dur(V2)=338ms, Dur(R2)=0.
Substituting the variables in 1<a< with the duration values in (0), we get the a range from the two speakers, shown in (0).
(0) Speaker YS: 1<a<1.703
Speaker VV: 1<a<1.695
Taking the smaller a range of the two, we know that 1<a<1.695.
The calculation here is not meant to show that we have successfully derived the a range. Rather, it is meant to demonstrate how to apply the general heuristics discussed in §3.1 to real languages to derive the a range. Our approach here is admittedly heuristic, but it is by no means circular. Upon observing a sufficient number of languages, we can hone in on a specific a range, and test its validity against further language data. The theory is falsifiable, since it makes concrete predictions about the contour tone bearing ability of syllable types (as indicated by CCONTOUR), and the predictions can be tested against the phonological patterning of contour tone distribution in languages.
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