Volume 56, Issue 1-2

The dynamic nature of vowel systems has recently been investigated in several English dialects confirming that phonetic disruptions often have systemic consequences and suggesting that change follows predictable patterns of movement. The present paper examines the nature of vowel change in Australian English by comparing two sets of data from different subjects at each end of a 25-year interval. A series of multivariate analyses of variance reveals significant acoustic differences between the two sets of data providing strong evidence for systemic effects. The analysis also indicates the presence of chain and parallel shifts within vowel classes as well as a close correspondence between monophthong and diphthong movement in phonetic space. The observed monophthong/diphthong relationships suggests that change in one class of vowels impacts on the other in a parallel fashion in this dialect of English.

Five male speakers produced the vowels of Greek at slow and fast tempo, in lexically stressed and unstressed syllables, and in lexically stressed syllables of words appearing in focus position. Duration, fundamental frequency (F₀), amplitude, and the frequencies of the first (F₁) and second formant (F₂) were measured. The effects on these variables of the phonemic category of the vowel, tempo, stress, and focus were examined. The results indicated that the vowel system of Greek follows universal tendencies in terms of duration but not in terms of F₀ and amplitude. Vowels in focus position, when plotted by their F₁ and F₂ frequencies, defined a vowel space larger than that defined by vowels in any other condition.

Prepausal postvocalic stops in English are reported to occur both with and without audible release bursts, more or less randomly, and this difference is said to be without distinctive function. However, there is evidence that an English final stop, absent its release, may be of reduced intelligibility, particularly as to its place of articulation. Without audible release a final stop’s place is conveyed mainly, perhaps entirely, by frequency shifts in the vowel formants. Among the vowels of English some are diphthongal, a property also signaled by formant shifts. The question arises: Is the intelligibility of an unreleased stop significantly affected by the phonetic nature of the vowel? Perceptual testing of appropriately chosen nonsense monosyllables ending in [p^⌍ t^⌍ k^⌍] indicates that these stops are generally somewhat less intelligible after diphthongs. However, not all three stops are affected equally, [k^⌍] perception being especially reduced in this context.

A number of experiments were carried out in order to test the hypothesis that categorical perception of speech stimuli is a function of synthetis quality – specifically, that the greater complexity of more natural speech stimuli makes it difficult for listeners to focus on particular stimulis parameters as psychoacoustic cues. The results show that there is an increase in categorical perception as synthesis quality improves from a simple synthesis by rule, via LPC synthesis, to a much more complex type called sinewave generation.

A general conclusion that has emerged from the collective results of a number of studies regarding acoustic characteristics of children’s speech production development is that both the duration and temporal variability of segments, words, and phrases tend to decrease as one considers increasingly older groups of children. While this conclusion is largely appropriate when considering averages for groups of children studied across intervals of several years, the limited amount of longitudinal data that exists suggests that similar patterns may not routinely be observed in the development of individual children, especially when shorter time periods are involved. Cross-sectional, acoustic studies have provided important general descriptions of speech production development, but additional longitudinal investigations are also needed to address issues that cannot be effectively evaluated utilizing cross-sectional data. For example, it was hypothesized in the present study that decreases in duration and variability would be greater when children were younger and that progressively smaller decreases would occur as they became older. Despite general tendencies for decreases in duration and variability to occur with increased age, it was also hypothesized that not all segments and words would be affected to the same extent in this regard. To consider these and related questions, the speech of 4 children was recorded approximately every 7–10 months for periods ranging from 4 to 6 years. There was some support for the notion that duration/variability decreases were greater when children were younger, but often this was not observed. It was also found that whereas some sounds/words decreased in duration across time, others remained relatively constant. Also, within the same word, certain segments became shorter across time, while others remained unchanged. These observations provide a perspective concerning speech production development that represents an important supplement to more general conclusions that have been obtained from group-oriented studies.