Lack of fear acquisition to film clip unconditional stimuli despite contingency awareness: Implications for electrodermal fear conditioning

Fear conditioning is most commonly assessed by measuring electrodermal activity to a conditioned stimulus (CS) in anticipation of an electric shock or another unconditioned stimulus (US). Replacing the electric shock with aversive film clips is an innovation that potentially has higher ecological validity for posttraumatic stress disorder. The present report examined boundary conditions of this paradigm across two between subjects experiments, with a particular focus on the effectiveness of film clip versus electric shock USs in promoting physiological fear conditioning. In Experiment 1, we tested whether fear acquisition was influenced by the inclusion of a shock US (n = 30), prior exposure to a longer trauma film (n = 29), or the use of face (n = 33) versus shape (n = 33) conditioned stimuli (CSs). Fear acquisition was enhanced by the inclusion of a shock US and to a lesser extent by prior trauma film exposure; however, conditioning in groups using film clip USs alone was characterised by lack of conditioned electrodermal responding. Experiment 2 investigated whether this absence of conditioned responding reflected reduced contingency awareness by measuring online US expectancy across film-based (four US film clip group with n = 55 and one US film clip group with n = 44) and shock-based (n = 30) US conditions, as well as salivary stress responses following acquisition. Despite equivalent US expectancy, CS pleasantness, and subjective US ratings across groups, conditioned electrodermal responses during acquisition were observed only in the shock US condition. Differences between groups may be explained by differences in salivary cortisol reactivity, with higher cortisol responses following acquisition in the shock group. Together, these findings indicate that shock USs increase physiological arousal, which appears to be essential for electrodermal reactivity, irrespective of conditioned learning processes. This finding has potentially important implications for the interpretation of electrodermal measurement in fear conditioning paradigms.