As they grow, children learn a lot about the world from what other people tell them. Along the way, they have to figure out who is a reliable source of information. A new study, which will be published in an upcoming issue of Psychological Science, a journal of the Association for Psychological Science, finds that when children reach around 4 years, they start noticing whether someone is actually knowledgeable or if they're just getting the answers from someone else.

Earlier studies have found that children as young as age three pay attention to whether someone is an accurate information source. If someone gives correct information, they'll go back to that person for more answers. But Shiri Einav of Oxford Brookes University in the UK thought there was more to the story. "If you give a correct response it doesn't necessarily mean you're knowledgeable" she says. "You could be accurate because you asked someone else for help or you could be accurate by a complete fluke." Einav and her coauthor, Elizabeth Robinson of Warwick University, wanted to know whether children assessing the reliability of others take into account the reasons for others' accuracy.

For their study, Einav and Robinson used puppets and a teddy bear to test children. A child would hold up a picture of an elephant, cow, or rabbit for each puppet to identify. Both puppets labeled all animals correctly but one puppet always knew the answer without any help, whereas the other puppet always relied on help from Ted. Then, Ted was removed so he couldn't help the puppets anymore and the child was given a picture of an unfamiliar animala mongooseand asked which puppet could tell them what it was.

Three-year-olds were equally likely to choose the puppet who'd known the answers on its own and the puppet that got help from Ted. But four- and five-year-olds were more discriminating: They invested more trust in the puppet whose accuracy reflected independent knowledge rather than being dependent on an external source. "We think it's important that from the age of around four, children are being sophisticated in a way that people hadn't really shown before," Einav says. "They're able to distinguish someone who's truly knowledgeable from someone who's given them a right answer but doesn't necessarily deserve long-term trust." This useful skill allows children to seek out people who are likely to be particularly beneficial for their learning.

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