Experimental procedure and setup.

<p>(a) Detection thresholds of vibration were measured in four conditions (2 fingers x 2 periods). In pre-period, 40% ethanol was applied to both fingers. In the post-period, the sanshool liquid was applied to the target finger and 40% ethanol was applied to the control finger. The assignment of the target finger was counterbalanced across participants. (b) Experimental setup and the sequence of a trial. Participants positioned their left index or middle fingertip on the piezo electric stimulator. The finger itself was supported by a board surrounding the stimulator. Beeps indicated the start and end of two stimulus presentation intervals, and vibration with random intensity (amplitude) was presented for 1000ms in the first or second interval. Participants were asked to report in which of the two periods the vibration was presented.