Figure 1

Experimental design. (A) Setup. We used an apparatus consisting of two cylinders that are connected via an air tube. A weight that was placed on the cylinder outside the scanner (not shown in the figure) pushes the cylinder inside the scanner via the air tube, which moved the stimulus onto the subject’s middle finger. The tactile stimuli had identical shapes and sizes, whereas their compliances, deformation per applied force, were varied. (B) Task schedule. In each trial, the fixation cross was replaced with one of the sound symbolic words, and the tactile stimulus was pushed onto the finger twice within 5 s. The subject was asked to judge the congruency of softness/hardness between tactile stimulus and sound symbolic words by pressing a button when the red fixation cross was presented. In the control condition in which randomized characters were presented and no tactile stimulus was given, the subject was asked not to respond.