Figure 1. An example of trial sequence.

At the beginning of each trial, an auditory instruction was given regarding the formation of task sets (Memory task set or No memory task set condition), followed by a 6-sec delay (Preparation period). Then the task execution period began with stimulus faces presented for 3-sec, followed by a 3-sec delay. During this 6-sec period, four single-digits were presented one at a time for 1.5-sec each, and the participants were asked to add them and remember the final answer. After the delay, a probe face was presented for 1-sec and the participants were given 3-sec to judge whether or not the probe face was among the three faces for the Memory task set condition. For the No memory task set condition, they did not have to respond to the faces. Then a two-digit number was presented for 1-sec and they were asked to decide whether or not the number was the answer to the addition.