Velocity measures in ultrasound data. Gestural timing of post-vocalic /l/ in English

We propose a new method for extracting dynamic information from midsagittal ultrasound images of tongue shape and location. The method is based on analysing parts of the tongue contour as they appear to travel up and down fan lines at key articulatory locations, representing velar and alveolar constrictions. The tongue displacement in these dimensions serves as the basis for calculating instantaneous velocity, whose maxima and minima help to define articulatory events. We validate the proposed method using data on /l/-darkening in Standard Southern British English. Our analysis extracts systematic information about the relative timing of gestures involved in the articulation of post-vocalic /l/, and it provides the basis for selecting representative images of consonantal constriction.