Comparison of stabilization systems for ultrasound research of speech

Carović, Ines. (2014). Comparison of stabilization systems for ultrasound research of speech. Govor : časopis za fonetiku, 31(2). pp. 87-108. ISSN 0352-7565

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Abstract

Ultrasound is one of the physiological methods for speech organs imaging. Since ultrasound cannot record both the tongue line and palate, detection of relative tongue line is harder (Stone, 2005a). The ultrasound beam passes through the tissue and reflects from the materials of different density (bone-muscle) or from air (tongue-air). This change is marked by a white line. Stabilization of the probe enables obtaining comparable results during whole testing with determined shift. During last 15 years ultrasound analysis has been developed and improved. Miller and Finch (2011) state that ultrasound recording becomes for articulatory phonetics what a spectrogram is for acoustic phonetics. This statement is confirmed by the fact that ultrasound is a rather cheap and safe method of recording speech organs in real time. Before the analysis of data obtained by ultrasound recording it is necessary to enable consistency in positioning the probe under the subject's chin as well as the stabilization of the subject himself/herself because every movement change the angle of the ultrasound signal transmission. In this paper different stabilization methods are compared. PHILIP (Phonetic immobilizer for laboratory investigation of production) enables stabilization of the probe under chin during the whole testing while SOS (system of basic stabilization) ensures stillness of subject's head. It gives a researcher an opportunity to place the probe in order to obtain the desired quality of the ultrasound result and to obtain the place of the probe that is specific to every subject and monitored event, respectively. The task of eight subjects who participated in the test was to pronounce 325 stimuli (sentences). Before every fiftieth reading of the stimulus the subject had to drink some water, swallow it, and keep the tonge on the palate. For each subject eight lines distant in time were obtained. The differences between the lines determined the movement of the probe. Specified movement of the probe enables correction of the method and its comparison to other systems. In this paper different stabilization systems of ultrasound probe in speech production research are compared. The description of stabilization system of probe (PHILIP) and subjects (S.O.S.) at the Department of Phonetics, University of Zagreb is given. Results of measurements of probe movement during testing are presented and they are compared with other stabilization systems developed in other laboratories for ultrasound speech research.

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