Figure 2.

The dynamic changes of SSD and StopAcc across Stop trials of one subject. The green vertical lines represent the successful inhibition (StopInhibit). The purplish red vertical lines represent the failed inhibition (StopResponde). The brown curve (left ordinate) represents the accuracy of Stop trials (StopAcc). The baby blue (right ordinate) curve represents the SSD value. To reduce participants’ anticipation of stimuli, two staircases were used and respectively started with SSD values of 250 and 350 ms (the first two values in the baby blue curve). The dark blue diamond points represent the first staircase with start value of 250 ms. The remaining baby blue diamond points represent the second staircase with start value of 350 ms. If the subject inhibited successfully on a Stop trial, the inhibition was made more difficult on a subsequent Stop trial by increasing the SSD by 50 ms; if the subject did not successfully inhibit, the inhibition was made easier by decreasing the SSD by 50 ms. There were four blocks with 48 Stop trials in total. In each block, six Stop trials corresponded to the first staircase, while the other six Stop trials corresponded to the second staircase. The order of the two staircases was randomized trial-by-trial. For continuity, the start values of the two staircases in block 2 were the last values in block 1, and so on. We can see from this figure that the StopAcc tended to be stable and was about 50% via the dynamical changing the SSD.