Fig. 1.

Schematic diagram of the Posner spatial cueing task. In the beginning, a ‘+’ sign was displayed in the center of a computer screen for 500 ms as the attention point. Then, an arrow sign was displayed at the attention point site for 200 ms as a cue, which randomly pointed to the left or right. After a random interval of 600–800 ms, a 3-cm-diameter dot was presented on the left or right side of the attention point for 1500 ms as the target stimulus. The participants were instructed to press a key to indicate the side of the target (‘F’ for left and ‘J’ for right) as quickly and as accurately as possible, which was followed by a 500-ms interval before the next task. Thus, the total time of a task trial was 3800–4000 ms.