The participants were asked to explore visually or haptically (with their right index finger, without visual control) the display and to give verbal instructions to the experimenter who moved the “central arrowhead” until they thought that its apex bisected the length of the rod. In both modalities, the starting position of the “central arrowhead” relative to the true middle was varied at each test trial. Two sides (right and left) and two lengths (55 mm and 65 mm) were presented. In the visual task, the display was hidden by a screen between each test trial so that this starting position could be modified by the experimenter. In total, each participant performed 4 test trials in each starting position in a randomised order in both tasks (i.e., 4 x 4 x 2 = 32 test trials per participant). In addition, a familiarisation phase was conducted before each modality task until the instructions were clearly understood (about 3 trials). In the haptic familiarisation phase, the experimenter guided the participant’s right index finger over all parts of the display and asked the participant to explore the display in this way during the experimental phase. No time constraint was imposed in the presentation phase of the stimulus or the response phase. The duration of each task was about 20 min. A 5-min break was inserted between the tasks. The duration of the whole session was about 45 min for each participant. The total time, as well as the perceptual error, was measured for each test trial.