Fig. 1.

a Experimental conditions of the cross-modal visuo-haptic mental rotation task. In the Aligned condition, viewing direction and hand orientation were aligned. In the Orthogonal condition, the hand was rotated counterclockwise by 90°. In the Delay condition, a 5 s temporal delay was introduced between the haptic and visual exploration of the stimuli. b Schematic view of the experimental setup. The participant looked in the mirror, which was positioned midway between the table and the projection screen. The visual stimulus displayed on the projection screen was seen via the mirror as if it were located on the table exactly in the same location as the haptic stimulus. Both arms were occluded. The right hand explored the haptic stimulus, whereas the left hand controlled the keyboard below the table. c Forms of the triangle wave function when the phase shift is or Depending on the experimental condition, different hypotheses (see main text) predict that the function might take these forms or a form with an intermediate phase shift