title: Using a radial ultrasound probe's virtual origin to compute midsagittal smoothing splines in polar coordinates.
abstract: 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.
authors.affiliation: Department of Linguistics, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.
authors.forename: Matthias
authors.initials: M
authors.lastname: Heyne
authors.affiliation: New Zealand Institute of Language, Brain and Behaviour, University of Canterbury, Private Bag 4800, Christchurch, New Zealand matthias.heyne@pg.canterbury.ac.nz, donald.derrick@canterbury.ac.nz.
authors.forename: Donald
authors.initials: D
authors.lastname: Derrick