During the training, the bonus score was calculated in real time directly after the completion of each FM epoch for the real-FB participants. To increase the specificity of the feedback and add an internal control, we fed back the differential fNIRS signals from the two regions of interest ( and ) to the participants. This has the advantage of canceling out any global unspecific effects due to factors such as generally increased blood flow.39–41 Specifically, we first calculated the percent signal change (PSC) at both ROIs. For instance, the value of the PSC at was defined as the difference between the mean value of [HbO] of an FM epoch and the mean value of [HbO] of the paired HM epoch shown right before the FM epoch, divided by the mean value of [HbO] of the HM epoch, i.e., , where is the index of the FM epochs (which is the same as the index of the HM epochs). Considering the time lag of the hemodynamic response, we removed the first 5 s of the signal while calculating the mean value for each epoch. Similarly, we calculated the value of PSC () at . Second, we calculated the difference between the two PSCs, denoted as . When both and were larger than zero, 40 bonus points were awarded to the participant; when both and were less than zero, zero bonus points were given; for all other conditions, the participant received 20 bonus points. For the sham group, the bonus points were generated for each training session before the task began: a set of numerical data with six zeros, five twenties, and five forties was randomly permutated before each training session to generate a data sequence to be used for the bonus points. At the end of the training task, the participant’s final score was shown on the screen.