**3.2.3 Stimuli**

There were three tasks, real walking (RW), virtual walking (VW), and walking observation (WO) in the experiment. During the RW task, the subjects walked on a treadmill at 1.0 km/h. For the VW task, a video clip was taken by a cameraman who was naturally walking down a corridor at 1.0km/h (Fig.14). Subjects were instructed to imagine as if they were actually walking from the first-person perspective. For the WO task, a video clip in which a person walks down the same corridor at 1.0 km/h was taken (Fig.14). Subjects were instructed to imagine that they were walking the same as the person in the video, especially to match their gaits to the video.

(a) Shooting location of the video

(b) Scene for walking observation. (c) Scene for virtual walking.

The subjects wore a video eyewear (Wrap920, Vuzix Corporation, NY, USA) with lightshield to block distracting outside light (Fig. 12), to display the video stimuli. This eyewear displays the video on a virtual 67-inch screen as seen from 10 feet. During the rest period between the tasks, a video clip in which there is a cross mark on a white board was displayed.
