Training Task

We used three versions of an adaptive running memory task for training, involving letters, animals and locations (Zhao et al., 2011, 2013). In the letters task (Figure ​(Figure1),1), a “+” focus point was displayed in the center of the screen to indicate task commencement. Subsequently, several letters were displayed one by one. The number of letters displayed varied among the different trial types (5, 7, 9, or 11 letters per trial). Each trial type was run an equal number of times in a random order. The participants were required to remember the sequence of the preceding three letters. After being presented with a blank bar on the screen, the participants were asked to use the keyboard to enter the sequence of the preceding three letters. Feedback was provided for each trial. Each letter appeared for 1750 ms; however, the difficulty level continually changed according to the participant’s performance. In this task, each participant completed six blocks and each block contained five trials. If three or more trials were completed correctly, the stimulus intervals were reduced by 100 ms in the subsequent block. By contrast, if two or more trials were completed incorrectly, the stimulus intervals were lengthened by 100 ms in the subsequent block. Each day’s training was based on the preceding day’s performance record for each participant.

Demonstration of letters running working memory (WM) task.

The animals task (Figure ​(Figure2)2) was identical to the letters task except animal images were used instead of letters. The locations task (Figure ​(Figure3)3) was identical to the letters task except visuospatial stimuli were used instead of letters. In each trial, a nine-square grid containing an image of a cartoon face was displayed in the center of the screen. The face could appear in any one of the nine squares. The participants were required to remember the sequence of the preceding three locations. The number of cartoon faces displayed varied among the different trial types (5, 7, 9, or 11 faces per trial). Every trial type was run in a random order. At the end of each sequence, the participants were requested to indicate the sequence of the preceding three locations by clicking in blank squares in a nine-square grid.

Demonstration of animals running WM task.

Demonstration of locations running WM task.