The cost of thinking about false beliefs: evidence from adults' performance on a non-inferential theory of mind task.

Much of what we know about other people's beliefs comes non-inferentially from what people tell us. Developmental research suggests that 3-year-olds have difficulty processing such information: they suffer interference from their own knowledge of reality when told about someone's false belief (e.g., [Wellman, H. M., & Bartsch, K. (1988). Young children's reasoning about beliefs. Cognition, 30, 239-277.]). The current studies examined for the first time whether similar interference occurs in adult participants. In two experiments participants read sentences describing the real colour of an object and a man's false belief about the colour of the object, then judged the accuracy of a picture probe depicting either reality or the man's belief. Processing costs for picture probes depicting reality were consistently greater in this false belief condition than in a matched control condition in which the sentences described the real colour of one object and a man's unrelated belief about the colour of another object. A similar pattern was observed for picture probes depicting the man's belief in most cases. Processing costs were not sensitive to the time available for encoding the information presented in the sentences: costs were observed when participants read the sentences at their own pace (Experiment 1) or at a faster or a slower pace (Experiment 2). This suggests that adults' difficulty was not with encoding information about reality and a conflicting false belief, but with holding this information in mind and using it to inform a subsequent judgement.