The absence of differential electrodermal responding in the second half of acquisition does not indicate the absence of fear learning.

Many contemporary studies of human fear conditioning exclude participants who fail to show differential electrodermal responding during late stages of acquisition training, deeming them to be non-Learners. The current study examined whether non-Learners, defined as those who fail to show larger electrodermal first interval responses to CS+ than to CS- in the second half of acquisition, show differential electrodermal responding early during acquisition or during extinction or evidence of fear-learning on other measures, including rated CS valence and contingency report. In a sample of 351 participants who completed a standard differential fear-conditioning paradigm that employed electrodermal first and second interval responses (FIR, SIR), continuous CS evaluations, and post-experimental contingency reports to assess fear-learning, 74 participants were identified as non-Learners. These non-Learners displayed overall smaller electrodermal responses but showed evidence for differential conditioning during acquisition in electrodermal FIR (block1) and SIR (blocks 2-3) and in CS evaluations during acquisition (blocks 2-4) and extinction (blocks 1-4). Fifty-nine non-Learners correctly reported the contingencies. A lack of differential electrodermal first interval responding during the second half of acquisition does not indicate the absence of fear-learning. Rather, this criterion appears to capture participants who exhibit low physiological arousal and performance decrements toward the end of acquisition. Applying criteria based on "end of acquisition" electrodermal responding to determine "non-learning" results in the exclusion of participants who display fear-learning at other experimental stages or in other measures.