Figure 1.

Example trials of the three conditions (2-digit, 1-digit, and letter) used in the fMRI session. In the encoding phase, participants were asked to memorize a sequence of six items which were presented sequentially at the rate of 2 s per item. In the recall phase, two items were presented at both sides of the screen, and participants were asked to judge which one came earlier by pressing the left or the right button. There were three judgments in one trial. Each trial lasted 22 s. The inter-trial interval (ITI) was set at 10 s. All cues are in Chinese.