Fig. 3.

A) The OptiTrack V120:Duo optical tracking camera is used to measure subject movement. The translations (x, y, z) and rotations (pitch, yaw, roll) are measured in the camera's frame of reference. B) The system uses infra-red LEDs to illuminate a series of 5 highly reflective markers (circled in red) positioned on the surface of the scanner-cast. These markers are combined to form a single rigid-body which is then tracked during an experiment. C) A series of 13 numbered marks were positioned within the field of view of the subject. The subject was instructed to shift their gaze to these marks. D) Approximate angular movements of the head required to shift the gaze to each mark.