Figure 1

Setup and dual task. (a) Setup. The participant stood inside the setup wearing headphones, holding the response panel with two push buttons in the left hand, and touching two touch sensors with right index finger and thumb. Vibration motors were attached to the right index finger and thumb. Near and far targets were in front of the participant each containing two touch sensors and four LEDs around each touch sensor. (b) Pure crossmodal congruency (CC) task. The participant had to hold the start buttons and an auditory cue signaled which target is going to be the reach target (near or far). The participant had to discriminate whether vibro-tactile stimulation was applied to the index finger or thumb by pressing the correct button on the response panel with the thumb of the left hand. A visual distractor was presented on one of the two touch sensors of the cued reach target simultaneously and spatially congruent or incongruent to the vibro-tactile stimulation. (c) Walk-and-reach CC task. The participant had to hold the start buttons and an auditory cue signaled which target is going to be the reach target (near or far). Upon the second appearance of the auditory cue (go cue), the participant needed to reach to the cued target either with the index finger on the top and the thumb on the bottom sensor (normal) or the other way around (inverse). The visuo-tactile stimulation could be before (static), at (onset) or after (move) the participant’s hand released the start button. (d) CC conditions. The panel displays all possible combinations of congruent and incongruent visuo-tactile stimulations and the corresponding correct response to the tactile discrimination. The reaching hand could be in a normal or inverted orientation at the target. For inverted hand orientation, which finger-distractor pairing is congruent depends on how congruency is defined. We calculated the CCE considering either definition. (Figure drawn by MB, photo by AG).