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J Acoust Soc Am. 2015 Dec;138(6):EL509-14. doi: 10.1121/1.4937168.

Using a radial ultrasound probe's virtual origin to compute midsagittal smoothing splines in polar coordinates.

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Department of Linguistics, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.
New Zealand Institute of Language, Brain and Behaviour, University of Canterbury, Private Bag 4800, Christchurch, New Zealand,


Tongue surface measurements from midsagittal ultrasound scans are effectively arcs with deviations representing tongue shape, but smoothing-spline analysis of variances (SSANOVAs) assume variance around a horizontal line. Therefore, calculating SSANOVA average curves of tongue traces in Cartesian Coordinates [Davidson, J. Acoust. Soc. Am. 120(1), 407-415 (2006)] creates errors that are compounded at tongue tip and root where average tongue shape deviates most from a horizontal line. This paper introduces a method for transforming data into polar coordinates similar to the technique by Mielke [J. Acoust. Soc. Am. 137(5), 2858-2869 (2015)], but using the virtual origin of a radial ultrasound transducer as the polar origin-allowing data conversion in a manner that is robust against between-subject and between-session variability.


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