Illusory or normative? Selective inferences about hidden causes can protect illusory causal beliefs

Our ability to extract causal information from direct experience is crucial in making sense of our world. It is therefore puzzling that people often overestimate the relationship between objectively unrelated events. Such causal illusions can be investigated in a contingency learning task, where participants judge the effectiveness of a cue in causing a target outcome based on their observed covariation across a series of trials. When cue and outcome co-occur (cell A trials), the outcome is readily attributed to the cue. But how do participants interpret outcomes in the absence of the cue (cell C trials), where the cause of the outcome is unspecified? We asked participants to provide open-ended (Experiment 1) or forced-choice (Experiments 2 and 3) explanations for trials in a causal illusion task where the cue was a medicine and the outcome was recovery from a disease. Participants inferred a range of plausible hidden causes for cell C recoveries (e.g., stronger immunity, less severe disease, spontaneous recovery). Critically, they rated these causes as less likely to be present on cell A trials, and those who attributed cell A recoveries only to the medicine showed the highest causal ratings for the medicine. Such a selective inference about the scope of a hidden cause may allow learners to explain away cue-absent outcomes that would otherwise undermine the perceived causal strength of the target cue, without violating normative principles. This mechanism may help explain how false causal beliefs can be maintained in the face of a null relationship.