Fig. 1

Flow Diagram of Experiment. (First, a pair of circles appeared on the screen with different colors (#1 and #2). After the subject pressed the corresponding key to select, the stimulus appeared in the selected circle for 500 ms. The subject needed to recognize the stimulus but not to react. A black screen after the stimulus disappeared was given for the subject to prepare for reaction. After that, the prompt “☆” appeared, and the duration is not limited. When seeing the prompt, the subject can answer whether he has seen it or whether the word is less than or equal to 3. Then a feedback (“ +2 ”or“ -2 ”) would be given. The feedback was preset, including 50% of “+2” and 50% of “-2”. The two kinds of feedback appeared randomly. The feedback lasted for 500 ms, then the subject would go to next trail)