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Research Article

A normative-speaker validation study of two indices developed to quantify tongue dorsum activity from midsagittal tongue shapes

Pages 484-496 | Received 15 Sep 2012, Accepted 18 Feb 2013, Published online: 07 May 2013
 

Abstract

This study reported adult scores on two measures of tongue shape, based on midsagittal tongue shape data from ultrasound imaging. One of the measures quantified the extent of tongue dorsum excursion, and the other measure represented the place of maximal excursion. Data from six adult speakers of Scottish Standard English without speech disorders were analyzed. The stimuli included a range of consonants in consonant–vowel sequences, with the vowels /a/ and /i/. The measures reliably distinguished between articulations with and without tongue dorsum excursion, and produced robust results on lingual coarticulation of the consonants. The reported data can be used as a starting point for collecting more typical data and for analyzing disordered speech. The measurements do not require head-to-transducer stabilization. Possible applications of the measures include studying tongue dorsum overuse in people with cleft palate, and typical and disordered development of coarticulation.

Acknowledgements

I am grateful to Nigel Hewlett for very helpful comments on an earlier version of this paper, to William Hardcastle for discussions, to Alan Wrench for advice on instrumentation and to two anonymous reviewers for advice and suggestions.

Declaration of Interest: This work was supported by ESRC grants RES-000-22-4075 and ES/K002597/1, and by an ESRC Postdoctoral Fellowship to the author (PTA-026-27-1268). The author reports no conflict of interest.

Notes

It is well known from ultrasound studies of tongue movement that endpoints of the tongue curve are unreliable parts of the image, as the imageability of these endpoints depends on the angle and position of the transducer, and front and back of the tongue can be obscured by the shadows of the jaw and the hyoid bone, respectively (Stone, Citation2005). Zharkova (Citation2013) suggests that when obtaining ultrasound data for calculating the indices it needs to be ensured that the tongue curve in the image stretches between the two shadows and that both shadows are visible in the image, which would minimize any differences in tongue curve endpoints across repetitions and across speakers.

One token of /fa/ for Speaker 6 was not recorded for a technical reason, so four repetitions of /fa/ were analyzed for this speaker.

In the recordings of Speakers 1–4, the precise level of articulatory/acoustic alignment was unknown, as there was no explicit procedure for automatic synchronisation of the ultrasound video signal with the acoustic signal (cf. Hueber, Chollet, Denby, & Stone Citation2008; Miller & Finch, Citation2011). Care was taken during the data analysis to ensure no obvious misalignment was present. This was done through inspecting several ultrasound frames before and after the acoustically annotated target (for example, by checking that the ultrasound frame corresponding to mid-/t/ had the most raised tongue blade out of a sequence of ultrasound frames surrounding this frame). Additionally, checks were made against the electropalatographic (EPG) signal, which was recorded at 200 Hz for Speakers 1–4 (albeit not used for analyses in this paper; for more details, see Zharkova, Citation2008), and was synchronized with the acoustic signal through time-aligned hardware pulses. For example, it was ensured that the target ultrasound frame for mid-/t/ coincided with the EPG frames showing alveolar closure.

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