Volume 56, Issue 3-4

As part of a project seeking a better understanding of the links between speech production and perception, we have conducted experiments on the perception of Thai word-final stop consonants by native speakers of Thai and native speakers of American English. The final stops of Thai are never released audibly. In English, however, final stops occur with and without audible releases. Previous work has shown that released stops are likely to be more intelligible than unreleased ones. That is, identification is better when information as to place of articulation in the formant transitions of the closing articulatory gesture is supplemented by acoustic information in a release burst. Both languages have labial, alveolar, and velar places of articulation, but Thai also has glottal closure. Two native speakers of Thai recorded sets of monosyllabic words minimally distinguished by the four final stops . Randomized lists of the isolated words were presented to 19 native speakers of English who responded with the labels ‘p’, ‘t’, ‘k’, and ‘other’. They were also presented to 30 native speakers of Thai for identification in Thai script as words. The highly significant differences between the two groups imply the possibility that the closing gestures of the Thai stops include a component that compensates somewhat for the absence of release, a component to which the English speakers are perhaps less well attuned. Such an interference will be tested in future work by tracking of the gestures in both languages with the Haskins Laboratories magnetometer.

Effects of speaking rate on the production of lexical tones (mid, low, falling, high, rising) were investigated in Thai. Stimuli consisted of bisyllabic adverbials (first syllable unstressed, last syllable stressed) elicited in a fixed syntactic and prosodic environment. For unstressed and stressed syllables separately, F₀- and time-normalized, fitted, third-order polynomial curves were used to compare height and slope characteristics of the tonal contours at each of 11 measurement locations between fast and slow speaking rates. Results indicated that speaking rate effects on F₀ contours of unstressed syllables are more extensive, both in terms of height and slope, than those of stressed syllables. In particular, the height of F₀ contours in unstressed syllables was generally higher in the fast speaking rate when compared to the slow. Analysis of the preceding carrier syllable revealed that changes in height of F₀ contours of unstressed syllables may be due primarily to perseverative effects of tonal coarticulation rather than to stress itself. The slope of F₀ contours in unstressed syllables varied depending on range of F₀ movement. Thai tones with substantial F₀ movement (falling, high, rising) exhibited overall flatter slopes at the fast speaking rate; those tones with lesser F₀ movement (mild, low) displayed steeper slopes. Despite extensive changes in height and shape, the five-way tonal contrast appears to be maintained in unstressed syllables at a fast speaking rate albeit in a different tonal space.

A production and a perception experiment were conducted to investigate the effect of speaking rate on the singleton/geminate consonant contrast in Italian. Acoustic analyses were performed of labial and dental singleton and geminate consonants produced in words spoken in isolation and in a sentential context at both a slow and a fast rate of speech. Closure duration was found to discriminate between the two categories of consonants within a given speaking rate. For one speaker, at a fast speaking rate the distribution of closure duration of geminate consonants was identical to the distribution of closure duration of singleton consonants produced in isolation. However, a measure reflecting the relation between two durations, the ratio between consonant duration and preceding vowel duration, discriminated between singletons and geminates both within and across speaking rates. The perception experiment tested whether manipulation of the consonant to vowel ratio would result in perceptual shifts. Results indicated that changing the ratio did affect perception of the geminate/singleton distinction. However, these effects varied greatly across listeners. Taken together, these findings provide support for the view that there are stable acoustic properties corresponding to phonetic features in that even though one type of temporal information, closure duration, is greatly affected by changes in speaking rate, a higher-order relational measure remains constant.

Of interest in the current study was how voice inset time (VOT) was influenced by changes in speaking rate across Spanish and English. Three groups of subjects (English monolinguals, Spanish monolinguals and early Spanish-English bilinguals) produced sentences containing voiced and voiceless bilabial stops at different speaking rates. As in previous research, English monolinguals showed rate-dependent effects on their VOT productions: VOT increased as speaking rate decreased. Spanish monolinguals showed a large effect of speaking rate on the duration of prevoicing of the voiced stops. However, they showed only a small effect of rate on the VOT of their voiceless stops. The bilinguals produced VOT values in each language that were nearly identical to their monolingual counterparts. The results from this study indicate that short-lag stops experience minimal variation as a function of speaking rate regardless of the other contrasting phonetic categories within a particular language. In addition, early bilinguals showed evidence of separate representations for voiced and voiceless stops for English and Spanish.

Investigations of the phonetics of infant-directed speech (IDS) have mainly focused on prosodic aspects, showing extreme values or overspecifications in comparison to adult-directed speech (ADS). On the other hand, studies of segmental properties, especially consonantal ones, are very rare. The lack of knowledge of phonetic characteristics of the infant’s speech input is problematic, considering that the infant’s perceptual development seems to be attuned towards properties in the ambient language, as suggested by infant perception experiments. In the present study voice onset time (VOT) was measured in Swedish mothers’ IDS and in their ADS. VOT was significantly shorter in IDS than in ADS in both voiced and voiceless stops. The impact of stress was very clear in both IDS and ADS, showing significantly longer VOT in stressed positions as compared to the unstressed. The results are discussed in a framework assuming a differential weighting system of different phonetic aspects such as prosodic, consonantal and vocalic, as a function of infant development.