Figure 4.

Schematic diagram of the training block. The training block began with a 1-minute baseline period, followed by 40 randomized task segments. During each task segment, the screen randomly displayed either an hourglass or a letter. If a letter was presented, the participant performed the activation mental task for 15 s, followed by the rest task (visual tracking of the TCD feedback signal) for 10 s. If an hourglass was displayed instead of a letter at the beginning of the segment, the participant continued to perform the rest task for an additional 15 s.