Cross-modal orientation discrimination experiment: haptic stimuli and results.

<p>Panel A shows the different haptic orientations used during the experiments. In the main experiment pairs of orthogonal haptic orientations were tested within every experimental block. In the cross-modal orientation discrimination experiment, clockwise and counterclockwise haptic orientations were tested in separate blocks, observers were required to judge to haptic orientation compared to the visual orientation during simulated binocular rivalry. Participants were forced to report whether the haptic stimulus was oriented “further clockwise” or “further counterclockwise” compared to the congruent visual stimulus (either +45° or -45° relative to vertical). Panel B reports the proportion of “further clockwise responses” plotted as a function of the mismatch in orientation between the haptic and the visual stimuli. The small coloured symbols represent individual observers’ performances (every colour representing a different observer), the big transparent grey dots represent the average performance. Even though a trend of improving performance with increasing visuo-haptic orientation difference is present, observers’ performance did not significantly differ from the average performance for visuo-haptic stimuli matched in orientation neither for the 7.5 degrees difference (one sample t-test, df = 4, t = 2.405, p = 0.074), nor for the 15 degrees difference for the 7.5 degrees difference (one sample t-test, df = 4, t = 1.95, p = 0.123), meaning that they were not able to discriminate the difference in orientation between visual and haptic stimuli within 15° difference. A (non significant) bias towards the “further clockwise” response was also observed when visuo-haptic stimuli were matched in orientation.