A common co-ordinate system for mid-sagittal articulatory measurement

Abstract

A standard practice in EMA articulatory measurement is to set the origin of the measurement space near the boundary of the upper incisors and gum, on a standard reference coil. A conventional horizontal dimension is defined as being parallel to the speaker's unique bite (occlusal) plane. We propose that this convention be extended to other instrumentation, with a focus on how it can be achieved for ultrasound tongue imaging (UTI) in particular, using a disposable and hygienic vacuum-formed bite plate of known size. A bite plane trace, like a palate trace, provides a consistent reference to allow images to be rotated and translated in case the probe is in a new location relative to a speaker's cranial space. The bite plane also allows speakers with differently shaped palates to be overlaid, and for ultrasound data to share a coordinate space with EMA. We illustrate the proposal using a sample of six speakers. The average bite plane slope could be used to retrospectively rotate ultrasound data that lacks bite-plane measurement