Figure 1.

Room preference scores for Paired group (n = 19, solid bars) and Unpaired group subjects (n = 15, open bars) before and after conditioning sessions with 20-mg d-amphetamine and placebo. The Paired group always received d-amphetamine in the room that they initially did not like, whereas the Unpaired group received d-amphetamine and placebo in both rooms. Bars represent mean ±SEM and asterisks indicate a significant difference between pre- and post-conditioning scores (Student’s paired t-test, P < 0.01)