“…In fear conditioning studies, it is often measured directly after presentation of a CS (first-interval response or FIR), or, in case of longer CS-US intervals, in the period prior to US delivery (second-interval response or SIR; Lovibond, Saunders, Weidemann, & Mitchell, 2008). In addition to measuring skin conductance during an anticipation period, one may also observe differential responding after unexpected omission of a shock US (i.e., on a non-reinforced CS+ trial after CS offset; Dunsmoor & LaBar, 2012;Spoormaker et al, 2011). This has been termed 'third-interval omission response' (TOR) or 'offset SCR' (skin conductance response)", and possibly reflects "surprise" or "relief" upon unexpected omission of the aversive US (Rescorla & Wagner, 1972;Spoormaker et al, 2011).…”