Fig 1. Feedback screen.

On the background of the feedback screen, either green or gray stripes moved from the right to the left side of the screen with a constant speed. During the resting period, the white dot in the middle of the screen overlapped a gray stripe of the moving background and was vertically fixed in the center of the screen (first, second and fifth example screens in the figure). During the feedback trials, the white dot overlapped a green stripe of the moving background and participants tried to move the white dot up by motor imagery of swallowing (third and fourth example screens in the figure). When they were successful, the number of reward points increased (green reward points indicated number of reward points obtained in the actual feedback trial, gray reward points indicated sum of all obtained reward points of all previous feedback trials).