Contamination in reasoning about false belief: an instance of realist bias in adults but not children.

Children aged around 5 and 9 years and adults were presented with stories and videos about a protagonist who heard a message purporting to provide factual information. Observing subjects knew whether the message was true or false. In some cases, this message contradicted the listener's existing belief based on what he or she had seen previously. Subjects judged whether the listener would believe or disbelieve the message. Child subjects frequently judged that a contradicting message would be disbelieved, irrespective of whether they (the child subjects) knew it to be true or false. In contrast, adult subjects made judgements that were contaminated by their own privileged knowledge of the truth. For three different scenarios, adult subjects judged more frequently that the message would be believed if they (but not the listener protagonist) knew it to be true, than if they thought it was false.