Fig. 1.

Experimental setup. This figure shows a subject standing in the tandem posture on the force platform over which the contour of the feet has been marked. The subject's state of vision was controlled via electronic goggles. A pulley system activated by a linear actuator pulling on a transparent cord (colored black here) allowed the experimenter to lower or raise a load cell, on which a wooden board (15 × 12 cm) was rigidly attached, to produce or withdraw haptic input passively with the index finger. The cord was hidden from the field of view of the subject by covering it with a tissue. Earmuffs were worn at all time to prevent the subjects from hearing any acoustic cues during the experiment. EMG, electromyogram.