Do CS-US pairings actually matter? A within-subject comparison of instructed fear conditioning with and without actual CS-US pairings.

Previous research showed that instructions about CS-US pairings can lead to fear of the CS even when the pairings are never presented. In the present study, we examined whether the experience of CS-US pairings adds to the effect of instructions by comparing instructed conditioning with and without actual CS-US pairings in a within-subject design. Thirty-two participants saw three fractals as CSs (CS(+)1, CS(+)2, CS(-)) and received electric shocks as USs. Before the start of a so-called training phase, participants were instructed that both CS(+)1 and CS(+)2 would be followed by the US, but only CS(+)1 was actually paired with the US. The absence of the US after CS(+)2 was explained in such a way that participants would not doubt the instructions about the CS(+)2-US relation. After the training phase, a test phase was carried out. In this phase, participants expected the US after both CS(+)s but none of the CS(+)s was actually paired with the US. During test, self-reported fear was initially higher for CS(+)1 than for CS(+)2, which indicates that the experience of actual CS-US pairings adds to instructions about these pairings. On the other hand, the CS(+)s elicited similar skin conductance responses and US expectancies. Theoretical and clinical implications are discussed.