Figure 2: Spatial location, pupil dilation responses and subjective rating
a) Spatial location control: heatmaps show the gaze position during a 10-second grey square (stimulus) in which the participant received a tactile stimulation. None of the four heat maps (depicting the 4 experimental conditions) showed any meaningful eye movements deviation from the stimulus presented on the center of the screen.b) Bar plot shows the Z-scored mean pupil size values normalized to baseline during Dynamic and Static touch promoted by a Human hand and Artificial hand. The inset on the left shows pupil dilation traces aligned to the time of Dynamic touch promoted by a Human hand (pink) and Artificial hand (yellow). The inset on the right shows pupil dilation traces aligned to the time of Static touch promoted by a Human hand (purple) and Artificial hand (light blue). The shaded traces represent ± s.e.m. centered around the mean. Vertical dotted grey line indicates the beginning of touch (10-second duration). The grey shaded area represents the analyzed epoch. c) Scatter plot shows the supralinearity effect by contrasting participants’ pupil size in Dynamic_Human condition alone (y-axis) against Dynamic_Artificial plus Static_Human conditions summed together (x-axis). d) Violin plots show the mean subjective ratings reported by participants in the four conditions: Dynamic touch promoted by a Human hand (pink), Dynamic touch promoted by an Artificial hand (yellow), Static touch promoted by a Human hand (purple), and Static touch promoted by an Artificial hand (light blue). Data points overlaid on top show each subject. In black it is depicted the mean and in red the median. ***, p < 0.001; **, p < 0.01; *, p < 0.05; n.s., not significant.