Figure 1: Experimental setting, variables, and spatial location control.
a) Experimental setting: the participants sat facing a computer monitor with their chin and forehead on a headrest to ensure stability and reduce any unintentional movement during pupil recording. They were invited to place their left arm on the table with their palm facing down. The researcher standing on the left side of the experimental subject performed different types of touch on either the dorsal side of the hand or the dorsal side of the forearm of the participant.b) Experimental variables: participants received a CT-optimal touch stroke velocity (a dynamic stroking with a speed of 3 cm/s) and CT-suboptimal touch velocity (a static touch). The nature of the stroking effector promoting the touch was either a Human hand or an Artificial hand.