Fig 1. Structure and time course of the experimental design.

(A) In the behavioral experiments, participants were asked to respond on which of the two stimuli felt rougher after active exploration with the tip of the right index finger. Each participant performed a total of 80 trials (16 trials × 5 blocks) and the maximum duration allowed per trial was 15 s. (B) In the fMRI experiments, the participants performed a total of 100 trials (20 trials × 5 blocks) and each trial included two periods: exploration for 6 s followed by rest for 15 s.