With the Qualysis motion-capture system, the position of reflectors placed on the face and body of the speaker can be tracked in three-dimensional space.
Placed on the corners of the lips, the reflectors can be used to measure lip width and protrusion. Lip aperture can be measured by reflectors on the upper and lower lips. A reflector on the chin provides an indirect measurement of jaw movement. A reflector between the eyes can be used as a reference point. The reflectors are extremely small (2.5 – 4 mm diameter) in order to track closely adjacent points on the face as accurately as possible. They must be handled carefully, and it takes approximately 20 minutes to prepare a speaker for an experiment, which entails positioning about 15 reflectors.
The system is used to study the movements of the speech articulators or the gestures that accompany speech production, in healthy speakers and those with pathologies.
In most cases the speaker reads from a written text, but it is also possible to record spontaneous speech. In order to ensure that the data are being acquired successfully, the experimenter watches the procedure on a screen that displays the images from four video cameras placed around the speaker. A larger number of cameras improves the reliability of the 3D reconstruction of the reflectors’ positions.