Figure 1. Procedure (main task).

(a) Observers tracked a moving ridge in the proximal to distal direction. In the tracking phase of the stimulus, v_prop (the red arrow) provides an estimate of the initial surface’s velocity. (b) The velocity of the surface changed in the distal portion of the workspace, causing v_tact (the light blue arrow) to deviate from zero. The observer, moving his or her hand at the same speed, reported the perceived direction of motion with respect to the world reference frame. (c) For comparison, the Filehne illusion in vision. The red and light blue arrows represent the target speed (estimated from eye pursuit) and the relative speed between target and background (estimated from retinal slip), respectively. Figure in panel c is adapted with permission from Ernst (2010).⁶