Table 2. Stop-signal Task Performance Measures.

Task measure	Stimulant-dependent individuals		Siblings		Controls
	Mean	SD	Mean	SD	Mean	SD
Go RT	411.43	71.69	434.62	69.17	407.34	74.25	NS
SSRT	233.96	51.66	211.46	51.08	199.44	56.59	P<0.05
Percent unsuccessful stopping	49.57	2.44	49.24	2.62	49.30	2.22	NS
Go SD	105.54	30.14	101.69	28.39	90.74	33.50	NS
Slowing following an unsuccessful stop	18.47	54.98	21.38	39.56	31.17	51.24	NS