An ANOVA of SCR and of US expectancy ratings with three, two-level factors – drug (THC, PBO), stimulus (CS+E, CS−), and time (early extinction [average first 4 trials], late extinction [average last 4 trials]) – revealed a significant main effect of time [SCR: F(1,27) = 11.79, p = 0.002; US Expectancy: F(1,27) = 26.82, p < 0.001], main effect of stimulus [SCR: F(1,27) = 9.95, p = 0.004; US Expectancy: F(1,27) = 31.16, p < 0.001], and interaction between time and stimulus [SCR: F(1,27) = 17.67, p < 0.001; US Expectancy: F(1,27) = 30.58, p < 0.001]. Both drug groups displayed significantly greater SCRs and US expectancy ratings to the CS+E during early extinction [SCR: THC = 0.34 ± 0.07; PBO = 0.27 ± 0.05 (Figure 2); US Expectancy: THC = 3.48 ± 0.23; PBO = 3.13 ± 0.25 (not shown)] compared to late extinction [SCR: THC = 0.13 ± 0.05; PBO = 0.13 ± 0.04 (Figure 2); US Expectancy: THC = 1.91 ± 0.33; PBO = 1.90 ± 0.32 (not shown)]. There were no differences between drug groups in
