Int. J. Environ. Res. Public Health 2009, 6 2019 Block by block comparisons between paradigms revealed a significant difference in CR production during reinforced trials at block 2 (t = 2.24; p = 0.03), block 4 (t = 2.20; p = 0.04), block 5 (t = 2.16; p = 0.04), and marginal significance at block 1 (t = 1.95; p = 0.06). Percentage of CRs on nonreinforced trials remained stable across learning blocks in both paradigms. Block by block comparisons showed no difference in CR production during nonreinforced trials between paradigms. Overall, Figure 3 reveals that alcoholics attained some level of differential learning during delay reversal learning, but no acquisition of differential CRs during trace reversal learning. Response Latency & Amplitude Independent samples t-tests of CR response latency during reinforced trials revealed that none of the measures differed significantly between paradigms (p’s > 0.12) during reversal learning (see Table 2). Similarly, there were no differences between paradigms for CR amplitude during reversal learning (p’s > 0.10) (see Table 2). There was, however, a significant difference in UR amplitude between delay and trace conditioning on reinforced trials during reversal learning (t = 3.31; p = 0.002) (see Table 3). Consequently, to ensure that the differences observed in acquisition were not confounded by a difference in unconditioned reflex to the airpuff, UR amplitude was entered as a covariate in an analysis of covariance (ANCOVA) of the mean percentage of CRs acquired on reinforced trials (paradigm as the between subjects variable). This analysis indicated that reversal UR amplitude was not a significant covariate (F = 0.772; p = 0.386). Table 3. Unconditioned Response Measure Means (standard deviation). Discrimination Reversal Delay Trace Delay Trace UR Amplitude CS+ 45 mV (16) 44 mV (16) CS+ 56 mV (20) 37 mV (15) CS- 12 mV (12) 10 mV (9) CS- 10 mV (5) 10 mV (9) Alpha Responses The number of short latency alpha responses did not differ between the groups (p’s > 0.4). The mean number of alpha responses across all trial types for the ALCs was 17 (SE = 4.95) and 19 (SE = 4.54) for the control participants.