Fig. 1.

Schematic time frame of cognitive tasks. (A) CST: a fixation cross was presented for 500 ms at the center of the screen 1. This was followed by display of the target stimulus for 200 ms. The targets presented were Chinese characters for different colors [red (), green (), blue () or yellow ()] either with same ink color as its meaning (congruent) or with ink different from the meaning (incongruent). The maximum response period was 1000 ms, which terminated at the time limit or when a key was pressed. This was followed by a 1000 ms inter-trial interval. Responses were collected through keys (‘d’, ‘f’, ‘k’ and ‘l’) labeled with the colors. (B) CDT: a central fixation was displayed for 1000 ms, followed by the memory array. This was one of three set sizes, with 2, 4 or 8 randomly arranged colored squares presented for 100 ms using a pool of highly discriminable colors for the squares (red, blue, violet, green, yellow, black and white). There followed a retention interval of 800 ms and subsequent presentation of a test array for 2000 ms. The participants had to respond by pressing the corresponding keys assigned ‘1’ if the test array differed or ‘2’ if it was the same as the initial stimulus.