Fig. 2

Experimental setup and procedure. (A) Robotic device with participant. (B) For each trial, the robot plantarflexed the participant’s ankle to two distinct positions or at two different velocities (reference vs. comparison). After experiencing two movements, participants indicated which movement was perceived further/faster (first or second). (C) Example of a derived stimulus-response psychometric function. The stimulus size difference corresponding to the 75% correct response rate represents the JND threshold indicated by the open circle. The IU corresponds the range between the stimulus size difference at 60-90th percentile indicated by the green double-headed arrow. (D) Timeline of the complete experimental procedure. Total duration was around 1.5–2 h including setup, practice, and breaks