Percent habituation scores (%Hab; ±SEM) of male rats (n = 8 per group) on the test day. Preweanling (PD 20), adolescent (PD 40), and adult rats (PD 80) were injected with saline or cocaine (2.5, 5, 10, or 20 mg/kg) immediately before testing. The right panels show data collapsed across the 12 time blocks. ‘a’ Significant difference between preweanling and adolescent rats. ‘b’ Significant difference between preweanling and adult rats. ‘c’ Significant difference between adolescent and adult rats.