Table 1.

Average Responding by Five-Session Block Over the Three Experimental Phases

	Operant level		Drug alone		Drug & VS Block 5 Sessions 21-25
Drug Group	Block 1 Sessions 1-5	Block 2 Sessions 6 -10	Block 3 Sessions 11-15	Block 4 Sessions 16 -20
SAL (n = 10)
Active	20.8 ± 1.6	13.2 ± 2.3	12.8 ± 2.3	11.0 ± 1.4	41.1 ± 7.9
Inactive	20.6 ± 2.1	14.9 ± 3.9	12.2 ± 3.2	12.3 ± 2.5	23.0 ± 7.7
ActRfq	0.51 ± 0.03	0.51 ± 0.06	0.56 ± 0.06	0.50 ± 0.06	0.66 ± 0.07
NIC (n = 10)
Active	20.0 ± 2.7	15.7 ± 3.4	14.1 ± 5.5	16.8 ± 4.1	53.4 ± 8.4
Inactive	16.4 ± 2.4	12.0 ± 3.8	18.4 ± 12.9	28.5 ± 19.8	34.2 ± 18.7
ActRfq	0.55 ± 0.05	0.58 ± 0.07	0.56 ± 0.07	0.55 ± 0.06	0.71 ± 0.05
METH (n = 9)
Active	16.6 ± 1.6	12.0 ± 1.8	32.0 ± 8.7	26.2 ± 7.2	73.0 ± 9.6
Inactive	21.8 ± 5.4	14.2 ± 4.0	36.6 ± 12.3	50.5 ± 21.1	40.0 ± 13.1
ActRfq	0.47 ± 0.05	0.52 ± 0.07	0.52 ± 0.05	0.46 ± 0.08	0.67 ± 0.05

Note. ActRFq = relative frequency of active responding. Active, inactive, and relative frequency of active responding are presented. Data are organized by drug group (saline [SAL], nicotine [NIC], methamphetamine [METH]). The relative frequency of active responding (ActRfq = active/[active + inactive]) indicates degree of preference for the active alternative. Values are the mean ± the SE of active and inactive responding emitted in each test session during the 5-session test blocks.