Apparatus
A PROPixx DLP projector (VPixx Technologies, Canada) was used to project the translating visual stimulus (a vertical Gabor patch) at a framerate of 120 Hz on a white, acoustically transparent projector screen 143 cm away from the subject. The projector had a spatial resolution of 1920 x 1080 pixels and cast a viewable image area 136 x 76 cm in width which corresponded to a visual angle of 57° x 32° and a visual resolution of 35 pixels per degree. The projector was connected via a DataPixx2 display driver and controlled using software written in MATLAB 2014a (The MathWorks, Inc.) running on an Apple Mac Pro computer and had a linearised luminance output. Participants gave their responses using a ResponsePixx (VPixx Technologies Inc.) button box.
A custom-made soundbar, consisting of 11 speakers (Visaton F8SC) fixed horizontally on a wooden support and aligned with the visual motion path, was used to deliver the moving auditory stimulus in free field. The soundbar was mounted on a wall 150 cm away from the subject at eye level and the linear separation of each speaker was fixed at 5° relative to the subject’s head (see Fig. 1). These speakers were controlled by two RME Fireface 400 audio interfaces (RME Audio) and were hidden from view by the large (169 x 100 cm) acoustically transparent projector screen sitting 7 cm in front of the soundbar.