Figure 1. Suppression effect of tactile stimulation on the visual orientation discrimination task (Exp. 1).

(A) Schematic illustrations of tactile and visual stimuli. A vibrator was set on the participant's left index finger of hand, which was covered by a black cloth. After presentation of a fixation point (0.6 × 0.6 deg) and a gray ring (2 deg in diameter, 0.05 deg in width) for 1200–2000 ms (randomly assigned in each trial), a visual target (0.5 × 0.5 deg) tilting either left or right was presented at the center of the ring for 20 ms. The target's contrast was either 0.12, 0.15, 0.18, 0.21, 0.24, or 0.27. The ring color was also changed from gray to black as the cue for the target onset. Tactile stimulation was concurrently applied for 200 ms. White noise bursts were also delivered through headphones to mask sounds emitted by the vibrator. After presentation of the target, participants were asked to judge the target's orientation. (B) Psychometric functions. Proportions of correct responses for visual discrimination were plotted against the target contrasts. The point of 75% responses of the functions (thresholds) and slopes were estimated. (C) Threshold and slopes. Threshold was increased when the tactile stimulation was applied (Touched condition) relative to when the sound (Sound condition) or no stimulus was presented (Without-Touched and Without-Sound conditions). These tendencies were not observed for the slopes. Error bars denote the standard error of the mean (N = 8). An asterisk indicates the condition was significantly different from the others (p < .05). Illustrations produced by and used with permission from Shoko Yabuki.