Table 1.

Behavioral data for experiments 1 and 2

Behavioral measure	Experiment 1	Experiment 2
Median correct Go RT (ms)	407.6 (11.9)	379.3 (16.8)
Median StopRespond RT (ms)	383.2 (13.2)	366.1 (14.7)
Median GoTrim (RT)	386.4 (11)	364.0 (13.7)
Number Go discrimination errors	1.7 (0.33)	3.0(0.55)
Mean SSD (ms)	220.2 (13.6)	190.0 (40.6)
Percentage inhibition	52.1 (0.8)	50.2 (2.2)
SSRT (ms)	187.4 (13.1)	189.3 (35.6)

Go RT is speed of responding on Go trials (without an error in response direction); StopRespond RT is the speed of responding on Stop trials for which the subject did not stop; GoTrim RT refers to a subset of trials from the Go RT distribution that are subsampled for each run, for each subject, to match StopRespond RT; Number Go discrimination errors is the number of errors in direction of response on Go trials; SSD refers to the average Stop-signal delay, computed from four staircases (see Materials and Methods) and point at which P(inhibit) ≈ 0.5; SSRT computed for each subject as Go RT − SSD. SEM is shown in parenthesis.