Measures of Phonemic Voice Quality in the Burmese Tonal Contrast
This paper describes an acoustic and glottographic experiment that examines the phonetic
nature of the phonological tone contrast used in the Burmese language. Descriptions of
the four Burmese tones in the literature are often conflicting (see Watkins 2005), but
most researchers agree that they differ phonetically in voice quality and pitch, as well as
in duration, intensity, vowel quality, and syllable structure (Bradley 1982, Thein Tun
1982, Javkin & Maddieson 1983, Watkins 2001). However, some of these properties, in
particular voice quality, have proven difficult to detect via indirect acoustic analysis
according to the studies described in Thein Tun (1982), Ladefoged, Maddieson, &
Jackson (1988), Watkins (1997), and Gruber & Feizollahi (2006). Instead, pitch contour
and duration were found to be far more robust indicators of the tonal categories. It is
significant though that the above studies have examined only tone-bearing syllables
elicited in isolation or within a frame of two surrounding modal low tones. The present
study provides glottographic data in addition to new acoustic data recorded in a number
of sentential contexts. These data are used to test the strength of the association between
voice quality and the four phonological tones. Results indicate an inconsistent
correspondence with voice quality, save for those cases where creaky or tense voice
quality is reported, for which the laryngealization is found to be context-dependent.
Ten native Burmese speakers were recorded while wearing EGG electrodes measuring
variation in vocal fold contact rates during speech. The stimuli consisted of twenty-two
tokens – representing three vowels in each tone, three nasal vowels in three of the tones,
and an additional unstressed, minor syllable token. The subjects read the tokens aloud in
isolation and embedded in seven frame sentences, which examined the following
contexts: (i) between low-toned syllables, (ii) between low and high tones, (iii) between
high and low tones, (iv, v) between each a low and high tone and an unstressed, toneless
syllable, (vi, vii) phrase-finally following each a low and high tone syllable.
The results of the study reveal a number of distinctions not always interpretable from the
acoustic pressure signal, most significantly tighter glottal constriction in creaky-toned
syllables. This constriction however was frequently neutralized in connected speech,
while other phonetic manifestations of lexical tone (e.g. pitch, intensity) were critically
not. This finding suggests that the heightened pitch of creaky tones occurs independent
of any laryngeal constriction, in contrast to phonological models (Green 2005, Lee 2007)
which treat the high F0 as a phonetic consequence of phonological voice quality
distinctions. For the other lexical tones, voice quality was not reliably indicated by rates
of vocal fold contact. Thus, the elevated pitch values of the high tone are likewise
independent of voice quality as there is no reliable association of the tone with
breathiness. In addition to providing a clearer picture of the laryngeal settings used in the
production of the tones, the study contributes insight into the shortcomings attested for
acoustic analysis of voice quality in Burmese, where the task is complicated by distinct
intensity levels, pitch targets, and vowel qualities found on each tone.
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