Procedure

The experiment was conducted in an isolated room. Each participant seated in front of a PC computer with a resolution of 800 × 600 pixels (approximately 100 cm from the eyes). Attentional shifting task and emotional picture recognition task were run using E-Prime 2.0 Software Package. The participants were instructed to respond to the stimuli as quickly as possible by using the dominant hand to press the button on a response pad. Before the main experiment, a short training session based on stimuli was employed. All the participants had completed all the trials of the two tasks correctly.

In the attentional shifting task, a fixation point appears in the center of the screen for 800 ms. Subsequently, the emotional pictures were presented for a duration of 1,000 ms, and then target stimuli (square or diamond) were presented. The subjects were required to judge the shape of the target picture. Participant should press the key of “1” if it is a square, and “0” if it is a diamond (see Figure ​Figure11).

Attentional shifting task. After the fixation, emotional pictures were presented for duration of 1,000 ms, and participants were asked to judge the shape of the picture. Participants press the key of “1” if it is a square and “0” if it is a diamond.

After attentional shifting task, participants had a 5-min break and then were asked to accomplish emotional picture recognition task. The instructions of the recognition experiment were as follows: a fixation point was showed in the center of the screen for 800 ms, followed by emotional pictures. Participants have to respond whether the emotional picture had appeared in the former task by pressing the key of “1” (appeared) or “2” (not appeared) (see Figure ​Figure22).

Emotional picture recognition task. Target pictures and interference pictures were presented following the fixation. Participants were asked to respond whether the emotional pictures had appeared in the former task by pressing the key of “1” (appeared) or “2” (not appeared).