Table 2. Stop-Signal Task Behavioral Data.

Group	Nonsmokers (n=25)	Smokers (n=25)
Median correct Go RT (ms)	490.87 (105.34)	506.36 (114.35)
Go discrimination errors	1.02 (1.25)	1.24 (1.63)
Mean Stop Signal Delay (ms)	301.59 (114.9)	322.93 (128.01)
Percentage inhibition	51.55 (7.28)	54.37 (7.28)
Stop Signal Reaction Time (ms)	189.28 (56.19)	177.88 (53.57)

Data are presented as means (SD in parentheses). No significant differences were noted between groups. Go RT is speed of responding on Go trials (without errors); Go discrimination errors is the number of errors in direction of response on Go trials; Stop Signal Delay (SSD) refers to the average Stop-signal delay, compared from two staircases (see Subjects and Methods), and is the point at which P (inhibit) ≃50% Stop Signal Reaction Time was computed for each subject as Go RT-SSD.