SCR for each CS trial was calculated by subtracting the mean skin conductance level during the 2 sec before stimulus onset from the highest skin conductance level that occurred in the 0.5 to 4.5 sec latency window after stimulus onset. SCRs below 0.02 μS were scored as zero (LaBar et al., 1998; Schiller et al., 2010). Raw SCRs were square root transformed to normalize the distributions and scaled according to each subject’s mean square root transformed US response (LaBar et al., 1998; Milad et al., 2005a; Orr et al., 2000; Schiller et al., 2010). To assess the level of conditioned responding in anticipation of the aversive US separate from unconditioned responses to the noise bursts, themselves, we included only non-reinforced trials of the CS+s in the analysis.
