Stabilization techniques for ultrasound imaging of speech articulations

One challenge for the ultrasound imaging of the tongue during connected speech is stabilization of both speakers heads and the ultrasound transducer. To accurately analyze tongue shapes, researchers must ensure that differences among images result from changes in tongue shape, not head or transducer movement. In this validation study, we present an inexpensive, space-saving technique for stabilizing the head and transducer during the collection of ultrasound images in the laboratory. Four speakers were video-recorded producing 5 blocks of 19 sentences each. The speakers’ heads were immobilized with a moldable head stabilizer (Comfort Company, model ♯HSM) affixed to a wall while the transducer was held by a microphone stand. Markers were attached to points on the speakers’ faces and the transducer. Custom-written MATLAB software was used to find the center of the markers for every 10th frame of the recordings. Results indicate that the transducer does not move, and head movement beyond the measurement error of 1 mm is confined to the first block, while speakers are adjusting to the equipment. As compared to other stabilization techniques Stone and Davis, J. Acoust. Soc. Am. 98, 3107–3112 (1995), this method provides equivalent immobilization that is significantly less expensive and portable for fieldwork.