Int. J. Environ. Res. Public Health 2009, 6 2017 stimulus contingencies, decreasing their CR production to the old CS+ and increasing CR production to the new CS+. T-test confirmed a significantly greater percentage of CRs during reinforced trials as compared to nonreinforced trials during delay reversal learning (t = 3.01, p = 0.007) indicating that abstinent alcoholics (ALC) were able to respond differentially on CS+ versus CS- trials and acquire the reversal of stimulus contingencies in the context of a delay paradigm (see Figure 2). ALCs produced a CR on 53 (SE = 6.3) percent of CS+ trials and 39 (SE = 3.9) percent of CS-trials during delay conditioning. However, a t-test revealed that during trace conditioning, the percentage of CRs during reinforced trials as compared to nonreinforced trials did not significantly differ (t = 0.139, p = 0.891) indicating that abstinent alcoholics (ALC) were unable to reverse the previously learned discrimination in the context of a trace paradigm (see Figure 2). ALCs produced a CR on 33 (SE = 5.6) percent of CS+ trials and 33 (SE = 5.4) percent of CS-trials during trace conditioning. T-test demonstrated a significant difference between the delay and trace paradigms in the mean percentage of CRs acquired on reinforced trials during reversal learning (t = 2.27, p = 0.03) indicating that participants produced more CRs on reinforced trials during delay reversal learning than trace reversal learning (see Figure 2). Figure 2. CR Acquisition. Mean percentage conditioned responses (CRs) for reinforced (CS+) and nonreinforced (CS-) trials during delay and trace conditioning.