X-ray Microbeam Data Research Articles

An Articulatory Study of Consonant-Induced Vowel Duration Changes in English

The effects of voicing, manner, and number of consonants on the duration of previous vowels in English can be created in three ways: by planned expansion or contraction of the entire vowel, by changing the relative timing of consonant and vowel gestures, or by modifying the duration of the closing movement for the consonants. An X-ray microbeam data base of 2 speakers of American English reciting monosyllabic words, which differed in their final consonants and in their position in the accentual structure of the utterance, was studied to evaluate these three accounts. In this data base, vowel duration differences due to the voicing of the following consonants were amplified by the presence of accent. Also, many of the duration differences associated with the following consonants are localized in the later portion of the opening movement, suggesting that subjects often create vowel duration changes by initiating the consonant closing gesture at an earlier or later time relative to the opening gesture.

Gestural specification using dynamically-defined articulatory structures

The types of analyses required within a framework that uses dynamically-defined articulatory gestures as the primitive units of phonetic description are outlined. The overall approach is then exemplified using investigations into an overlap hypothesis of reduced vowels, specifically the hypothesis that the difference between the bisyllable “beret” and the monosyllable “bray” can be attributed to a difference in the overlap of the labial closure and tongue rhotic gestures. This overlap hypothesis is supported by a perceptual test of simulations of the utterances as well as by preliminary articulatory analyses of X-ray microbeam data, and leads to some possible overlap typologies for reduced syllables.

A three-dimensional model of tongue movement based on ultrasound and x-ray microbeam data

Point-tracking techniques provide timing information about structural movements of the tongue. Imaging techniques provide information about cross-sectional and pharyngeal tongue shape and movement. This study joined these techniques in a single subject. Five pellets on the tongue surface were tracked using x-ray microbeam, and the midsagittal and coronal planes of the tongue were imaged using real-time ultrasound. The speech materials were the consonants [s] and [l] and the vowels [i], [a], and [o] combined in VCVCe utterances. Analyses concentrated on the difference in tongue movements related to the two consonants. A model of tongue movement was developed, in which critical features of consonant shape and position dominated the tongue opening movement. In this model, the tongue is divided into subdivisions termed "functional segments" in both the sagittal and coronal planes. Movements of the functional segments created observable opening movement patterns.

X-ray microbeam method for measurement of articulatory dynamics-techniques and results

Features of the X-ray microbeam method in the observation of articulatory movements are discussed, and an analysis of the dynamic characteristics of several speech organs based on X-ray microbeam data are presented. Experience with the use of the X-ray microbeam system has confirmed that a substantial reduction in X-ray dosage can be achieved. The movements of 6 pellets on the tongue and teeth are tracked at a rate of more than 100 frames per second, with an effective exposure area of about 1 cm 2 per frame, and with an exposure rate of 120 mR per minute in this area. Approximation of the movements of the pellets on the tongue, jaw and velum by means of the step response of a linear second order system has revealed that there are considerable differences in the values of the time constant among these speech organs. The duration of the step command also varies according to the type of vowel. These differences are reflected on the undershoot pattern and on the pattern of the coarticulation between consonant and vowel. The investigation of the movements of the velum has showed that a simultaneous observation of EMG is important for interpreting the pattern of the underlying motor control.