2.6. VDT Operation
The VDT operation consisted of playing a video game with a smartphone for 30 min. On the smartphone screen, 41 identical kanji characters and one similar but different kanji character were displayed (seven vertical by six horizontal; 42 characters in total). The participants tapped on the different ones displayed as soon as they found them. If the subject tapped correctly, another task (another 42 kanji characters) was displayed, and the subject repeated the task (finding and tapping different kanji characters). Additionally, a 30 cm cord was attached to the smartphone, and the subjects wore the cord around their necks to maintain a constant distance between their eyes and the smartphone while performing the VDT operation.