Siripong Potisuk

Acoustic Correlates of Stress in Thai

Acoustic correlates of stress [duration, fundamental frequency (Fo), and intensity] were investigated in a language (Thai) in which both duration and Fo are employed to signal lexical contrasts. Stimuli consisted of 25 pairs of segmentally/tonally identical, syntactically ambiguous sentences. The first member of each sentence pair contained a two-syllable noun-verb sequence exhibiting a strong-strong (--) stress pattern, the second member a two-syllable noun compound exhibiting a weak-strong (--) stress pattern. Measures were taken of five prosodic dimensions of the rhyme portion of the target syllable: duration, average Fo, Fo standard deviation, average intensity, and intensity standard deviation. Results of linear regression indicated that duration is the predominant cue in signaling the distinction between stressed and unstressed syllables in Thai. Discriminant analysis showed a stress classification accuracy rate of over 99%. Findings are discussed in relation to the varying roles that Fo, intensity, and duration have in different languages given their phonological structure.

Lexical tones in Thai after unilateral brain damage

An acoustic perceptual investigation of the five lexical tones of Thai was conducted to evaluate the nature of tonal disruption in patients with unilateral lesions in the left and right hemisphere. Subjects (n = 48) included 10 young normal adults, 10 old normal adults, 11 right hemisphere nonaphasics, 9 left hemisphere fluent aphasics, and 8 left hemisphere nonfluent aphasics. The five Thai tones (mid, low, falling, high, rising) were produced in isolated monosyllables, presented for tonal identification judgments, and measured for fundamental frequency (Fo) and duration. Results of an analysis of variance indicated that left hemisphere nonfluent speakers signaled and tonal contrasts at a lower level of proficiency. The extent of their impairment varied depending on severity level of aphasia. When compared to normal speakers, tonal identification for less severe nonfluent aphasics differed more in degree than in kind, and for more severe nonfluent aphasics differed both in kind and in degree. Acoustic analysis revealed that with the exception of one left nonfluent, average Fo contours were comparable in shape across speaker groups. Variability in Fo production, however, was greater in left nonfluent speakers than in any of the other four groups of speakers. Issues are discussed regarding the extent and nature of tonal disruption in aphasia and hemispheric specialization for tone production.

Classification of Thai tone sequences in syllable-segmented speech using the analysis-by-synthesis method

Tone classification is important for Thai speech recognition because tone affects the lexical identification of words. An analysis-by-synthesis algorithm for classifying Thai tones in syllable-segmented speech is presented that uses an extension to Fujisakis (1983) model for tone languages that incorporates tonal assimilation and declination. The classifier correctly identifies all of the tones in 89.1% of the test utterances.

Publications Received for Review

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Inter- and intraspeaker variability in fundamental frequency of Thai tones

Abstract A measure was obtained of variability in fundamental frequency ( F 0 ) in citation forms of lexical tones. The language selected for investigation was Thai, a tone language with five lexical tones: mid, low, falling, high and rising. Twenty speakers participited in the experiment: 10 “young” male speakers and 10 “old” speakers, 5 male and 5 female. High-quality tape recordings were obtained of each subjects productions of a minimal set of five monosyllabic words. F 0 contours were extracted by a cepstral analysis. A comparison was made of inter- and intraspeaker variability in the production of the five Thai tones. Results of analysis of variance indicated that the degree of intersubject variability in F 0 was greater than intraspeaker across all five tones, that young and old speakers exhibited the same pattern of variability, and that variability in tone production differed depending on the lexical tone. The falling and rising tones exhibited smaller degrees of variability than the mid, low or high. Findings are interpreted to highlight the nature of F 0 variability, the relationsip of F 0 variability to amount of F 0 movement, and crosslinguistic differences in F 0 variability as a function of prosodic structure.

Tonal coarticulation in Thai after unilateral brain damage.

The magnitude and temporal extent of anticipatory and perseverative tonal coarticulation was investigated in Thai-speaking normal and brain-damaged adults. A total of 47 speakers (10 young normal, 10 old normal, 13 nonaphasic right-brain-damaged patients, 14 left-brain-damaged aphasic patients, 9 fluent, 5 nonfluent) produced all 25 possible sequences of two tones from the five lexical tones of Thai embedded in a carrier sentence. F0 contours were analyzed in terms of height and slope at 10% intervals throughout the duration of the two syllables. Acoustic analysis revealed that anticipatory and perseverative tonal coarticulation of tones was markedly reduced in left fluent aphasics, totally absent in left nonfluent aphasics, but reasonably intact in right hemisphere patients. Findings are interpreted to highlight the nature of speech disturbances in nonfluent and fluent aphasia, hemispheric specialization for tone, and tonal coarticulation in Thai.

Interaction between Tone and Intonation in Thai after Unilateral Brain Damage

Intonational characteristics of Thai sentences were used to evaluate fundamental frequency (F(0)) control in brain-damaged patients with unilateral left and right hemisphere lesions. Subjects (n = 41) included 9 young and 10 old normal adults, 12 right hemisphere patients, and 10 left hemisphere aphasic patients (7 fluent and 3 nonfluent). Sentences were comprised of six words, three of which were keywords occurring in sentence-initial, -medial, and -final positions. All 125 possible sequences of three of the five Thai tones (mid, low, falling, high, rising) were superimposed on monosyllabic keywords. Utterances were produced at a conversational speaking rate. Average F(0) of keywords was analyzed as a function of sentence position, tone, and group. For both normal and brain-damaged speakers, results indicated that tones in sentence-final position were significantly lower in F(0) than in either sentence-initial or -medial position; falling and high tones were significantly higher in F(0) than mid, low, and rising tones. Findings are discussed in relation to issues pertaining to hemispheric specialization and the nature of F(0) deficits in nonfluent and fluent aphasic patients.

Speaker-independent automatic classification of Thai tones in connected speech by analysis-synthesis method

Tone classification is a crucial component of any automatic speech recognition system for tone languages. It is imperative that tonal information be incorporated into the word hypothesization process because patterns of pitch (or tones) contribute to the lexical identification of the individual words. In this paper, we present a novel algorithm for automatically classifying Thai tones in connected speech using an analysis-synthesis method based on an extension to Fujisakis model. We have successfully incorporated into the model two major factors affecting the phonetic realization of tones in connected speech: tonal coarticulation and declination. Also addressed is an F/sub 0/ normalization procedure for achieving speaker-independence. In our preliminary experiment, we were able to achieve 89.1% classification accuracy.

Vowel length and stress in Thai

Abstract It has been hypothesized that the relative importance of phonetic correlates of stress varies depending on the phonological structure of a language. If phonetic resources are used up in lexical phonology, it is predicted that they are unavailable or minimally available for signaling stress. Duration, one of the principal phonetic correlates of stress, is used to signal vowel length contrasts in Thai. The primary aim of this study was to examine the effects of stress on duration in signaling vowel length contrasts in Thai running speech. Stimuli consisted of 16 pairs of segmentally and tonally identical sentences representing four types of structural ambiguity and two types of stress patterns. In half of the pairs, keywords contained long vowels; in the other half short vowels. Syllable types of keywords were varied on the basis of the coda: nasal-ending vs. nonnasal-ending.Measures were taken of the duration of the vowel, nonvowel, and vowel + non-vowel intervals associated with keywords. All thr...

Anticipatory Tonal Coarticulation in Thai Noun Compounds after Unilateral Brain Damage

The time course and extent of anticipatory coarticulation between tones was investigated in normal and brain-damaged Thai-speaking subjects. Subjects were classified into five groups including 11 young normal, 9 old normal, 12 right hemisphere, 9 left hemisphere fluent, and 6 left hemisphere nonfluent. Stimuli consisted of five bisyllabic noun compounds with a falling tone on the initial syllable and each of the five Thai tones (mid, low, falling, high, rising) on the final syllable. Height and slope of F0 was measured at 10% intervals throughout the duration of the initial syllable. Results indicated anticipatory effects on both height and slope of the falling tone. Height effects extended throughout from the beginning. The falling tone was generally higher when occurring before the low/rising tones than when occurring before the mid/falling/high tones. Slope effects were restricted to the terminal portion. The falling tone before low/rising tones exhibited a steeper slope than before falling/high tones. In magnitude of effect, patients with left and right hemisphere lesions were statistically indistinguishable from those of normal subjects. No differences were noted in coarticulatory patterns as a function of aphasia type. All brain-damaged speakers were more variable in F0 production than normals. Findings are interpreted to highlight properties of nonfluent aphasic speech and neurological bases of speech production.