Yarritu Corrales, I. & Matute, H.
Universidad de Deusto, Bilbao, Spain
In two experiments we test how the presentation of biased information before the actual experiment can induce causal illusions. The potential cause was a fictitious medicine and the effect was recovery from a health crisis. Group Induced was pre-informed about the number of patients in which the effect (recovery from the crisis) occurred when they took the medicine. Group Warned was pre-informed about the number of patients that had recovered without taking the medicine. Both groups were then presented with 100 trials (one per patient). In Experiment 1 the patient could have taken the medicine or not and could feel better or not. The drug-recovery contingency was zero. However, participants in Group Induced showed an illusion that the drug was effective. In Experiment 2 the medicine had to be administered (or not) by the participant (rather than the patient). In this case, our pre-information manipulation resulted in participants in Group Induced administering the drug significantly more often than participants in Group Warned. This in turn produced a larger number of coincidences between the drug and the recovery and a larger illusion. In other words, the illusion of causality was mediated by the behavioral increase produced by the pre-information manipulation.