Int. J. Environ. Res. Public Health 2009, 6 2015 (optimally, a CR will peak just before the onset of the airpuff). The CR amplitude is measured as peak amplitude and refers to the amount of EMG muscle activity during a CR. UR amplitude is measured as peak amplitude and refers to the amount of EMG muscle activity during the UR period, and reflects the unconditioned reflex in response to the airpuff. 3.1. Discrimination Learning Conditioned Response Acquisition Independent samples T-test confirmed a significantly greater percentage of CRs during reinforced trials as compared to nonreinforced trials during delay discrimination learning (t = 4.32, p = 0.001) indicating that abstinent alcoholics (ALC) were able to respond differentially on CS+ versus CS- trials and acquire the initial discrimination in a delay paradigm (see Figure 2). ALCs produced a CR on 58 (SE = 4.3) percent of CS+ trials and 37 (SE = 5.1) percent of CS-trials during delay conditioning. Similarly, a t-test confirmed a significantly greater percentage of CRs during reinforced trials as compared to nonreinforced trials during trace discrimination learning (t = 3.32, p = 0.004) indicating that abstinent alcoholics (ALC) were also able to respond differentially on CS+ versus CS- trials and acquire the initial discrimination in the context of a trace paradigm (see Figure 2). ALCs produced a CR on 45 (SE = 5.3) percent of CS+ trials and 29 (SE = 4.2) 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 discrimination learning (t = 2.04, p = 0.05) indicating that although alcoholics were able to acquire the initial discrimination during both delay and trace paradigms to some degree, participants produced more CRs on reinforced trials during delay discrimination learning than trace discrimination learning (see Figure 2). Difference Scores Difference scores were calculated by subtracting the mean percentage of CRs during nonreinforced trials from the mean during reinforced trials (Difference Score = %CRs on CS+ trials minus %CRs on CS- trials). Alcoholics’ difference score during delay discrimination learning was 21 (SE = 4.9). Alcoholics’ difference score during the trace discrimination learning was 16 (4.8). T-test on the mean differential learning scores revealed there was no significant difference between delay and trace differential CRs during discrimination learning (t = 0.786, p = 0.437). Learning Curves As can be seen in Figure 3, when conditioning trials were collapsed into six blocks of five trials each, the ALC participants demonstrated an overall increase in the percentage of CRs across the six discrimination learning blocks of reinforced trials during delay conditioning, peaking at block 4 and remaining moderately steady across blocks 5 and 6. T-tests on mean percentage of CRs acquired block by block confirmed significant differences between blocks 1 and 3 (p = 0.01), blocks 1 and 4