Int. J. Environ. Res. Public Health 2009, 6 Difference Scores 2018 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 - %CRs on CS- trials). Alcoholics’ difference score during delay reversal learning was 16 (SE = 4.8). Alcoholics’ difference score during the trace was 0.6 (SE = 4.2), indicating that alcoholics were unable to achieve differential learning during the trace reversal task. This was confirmed by a t-test on the mean differential learning scores, in which there was a significant difference between delay and trace differential CRs during reversal (t = 2.08, p = 0.045). 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 relatively flat production in the percentage of CRs across the six reversal learning blocks of reinforced trials during delay conditioning, peaking at blocks 3, 4 and 6. T-tests on mean percentage of CRs acquired block by block showed no significant differences across learning blocks during delay reversal learning. Despite the flat curve, there is evidence of some increased acquisition over trials with rapid learning in the first block. The learning curve for trace conditioning was less consistent and showed no evidence of acquisition across blocks and no evidence of rapid acquisition in block 1 as seen in the delay paradigm. T-tests on mean percentage of CRs acquired block by block confirmed no significant differences across learning blocks during trace reversal learning. Figure 3. Learning Curves: Conditioning trials were collapsed into six blocks of five trials each. Difference Scores were calculated for each block by subtracting the mean percentage of CRs during nonreinforced trials from the mean during reinforced trials (Difference Score = %CRs on CS+ trials - %CRs on CS- trials).