Circle Tracing Test (CTT, Bachorowski & Newman, 1985) This task requires subjects to trace a large printed circle (20 inches in diameter) with their index finger to measure inhibition of an ongoing response (eg. Geurts et al, 2004; Scheres et al., 2003). The word START (in green ink) was printed on the right side of the line and the word STOP (in red ink) was printed on the left side. The task was administered under two conditions: first with neutral instruction ('trace the circle') followed by inhibition instruction ('trace the circle again, but as slow as you can this time') within 12 minutes without subject's knowledge. The dependent variable on this task included time 1 under neutral instruction, time 2 under inhibition instruction, time discrepancy referred to time 2 minus time 1, and a three-point (0-2) degree of deviation score assessed by the trained observer. The larger the time discrepancy, the better a participant is able to inhibit (slow down) the continuous tracing response.