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During an experimental task, a prompt sign “+” is displayed in the center of the screen to signal the start of that task. In the experimental task, the five letters of the alphabet “B, D, L, Y, and P” were presented as stimuli, and each letter would appear separately in the center of the display, with a stimulus presentation time of 2 s and a stimulus interval of 2 s. Subjects were asked to look at the letters carefully and press the “F” key if the letter presented was the same as the previous one presented, or the “L” key if different. The formal test was divided into 2 segments; each segment had to be completed 24 times and practiced 12 times before the formal test.