Induction of compulsive checking as identified by formal performance criteria. Performance measures are in reference to the home base established by the rat on the tenth open field test shown here, and recognized as the locale with the longest total duration of stops. Quinpirole-treated animals (hatched bars) met compulsive checking criteria because compared to saline-treated rats (crosshatched bars), they showed: (A) more frequent returns to the home base, (B) a higher than an expected rate of returning to the home base, (C) more rapid returns to the home base, and (D) fewer visits to other places on trips from the home base. *p < .05, t test. Values are mean and SEM.