Figure 2.

Illustration of the four perturbation types. a, Rotation perturbations: visual space was rotated around the target, such that position of the virtual fingertip was displaced relative to the unseen finger, but the direction of motion relative to the target was unchanged. b, Direction perturbations: visual space was rotated around a point just past the occluder, along the line connecting initial and target positions. The position of the virtual fingertip initially coincided with the actual finger, but its direction of motion was different. c, Step perturbations: visual space was displaced in the direction perpendicular to main axis of movement. This changed both the position of the virtual fingertip and its direction of motion relative to the target. d, Opposing perturbations: visual space was rotated around a point between the target and the emergent point. This also changed both the position and the relative motion of the virtual fingertip, but in opposite directions compared with step perturbations.