Time Discrimination Task Time discrimination task, modified from Smith et al. (2002) presents the green circle on the left first, followed by the red circle on the right. The subject is asked to press the key to indicate the circle with longer duration. The standard stimuli and comparison last for 1000ms, and 1350ms, respectively. The two circles are randomly presented. If the answer is correct, the comparison duration decreases in 15ms; if the answer is wrong, the comparison duration increases in 15ms. The task continued either until the subject had made six reversals, or until 20 trials, whichever occurs first.