The effect of linear vection on manual aiming at memorized directions of stationary targets

Stationary observers were required to aim manually at either a straight-ahead, or a lateral, immobile target (0 degrees and 20 degrees of eccentricity, respectively). First, they aimed at a perceptually present target. Second, they aimed at the memorized direction of the target. Third, they aimed at the memorized direction of the target after a 4 s period of forward sagittal vection. The comparisons of the post-vection versus ante-vection aimings at the memorized direction of the targets reflect an illusory increase in the eccentricity of the lateral target, and no change in the direction of the straight-ahead target. These results objectivate the idea that forward sagittal vection (a particular case of linear vection) corresponds to an illusion of self-displacement, ie an illusory change of body place through space.