Figure 2: 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) On the top, pupil dilation traces aligned to the time of CT-optimal touch promoted by a Human hand (pink) and Artificial hand (yellow). The shaded traces represent ± s.e.m. centered around the mean. Vertical dotted grey line indicates the beginning CT-optimal touch (10-second duration). The grey shaded area represents the analyzed epoch. On the bottom, pupil dilation traces aligned to the time of CT-suboptimal touch promoted by a Human hand (purple) and Artificial hand (light blue). c) Bar plot shows the Z-scored mean pupil size values normalized to baseline during CT-optimal and CT-suboptimal touch promoted by a Human hand and Artificial hand. d) Scatter plot shows the supralinearity effect by contrasting participants’ pupil size in CT-optimal_Human condition alone (y-axis) against CT-optimal_Artificial plus CT-suboptimal_Human conditions summed together (x-axis). e) Violin plots show the mean subjective ratings reported by participants in the four conditions: CT-optimal touch promoted by a Human hand (pink), CT-optimal touch promoted by an Artificial hand (yellow), CT-suboptimal touch promoted by a Human hand (purple), and CT-suboptimal 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.