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Why do children believe in Santa? PLOS ONE studies examine how children conceive truth

How old were you when you stopped believing in Santa Claus? Evidence shows you were probably about five years old. But why then? Why not three or seven?

Before you wrap up a present for your niece or nephew this holiday season, you should know that there is something special about turning five. Just about everyone’s brain develops a new ability at that age, the ability to think that other people’s thoughts about the world may not reflect reality. Thus, unlike younger children who accept all assertions trustfully, most five-year-olds can reason that your beliefs might actually be false.

As adults, we effortlessly tell stories to explain others’ actions

Adults know that behavior is driven by a person’s mental state (such as an individual’s beliefs, desires and goals), rather than by the objective truth. In fact, most adults understand and describe behavior by constructing a narrative about the actor’s feelings and thoughts. In 1944, Fritz Heider and Marianne Simmel made a short video that lets you try yourself. Watch the movie before reading the next paragraph.

What did you see?

Many people who watch the video interpret the movements of cartoon shapes as caused by thoughts and emotions, saying things such as: “The big triangle is bullying the smaller one”; “The circle wants to help his friend but is scared” or “The big triangle is angry.” Remarkably, all viewers in the nonclinical population ascribe mental states to the cartoon shapes, with nobody saying that they saw a video about moving two circles and a triangle. Cartoons such as the Heider and Simmel video are a prize find for social psychologists, because they show that humans are quick to attribute mental states to objects even from a minimal sequence of images. In social perception, abilities to reason about the mental states (such as beliefs, desires, goals, personality or emotions) of other people are referred to as Theory of Mind (ToM).

 A static image from a Heider-Simmel animation may look like this (an artist's reconstruction). Image credit: Liz Little (modified with permission).
A static image from a Heider-Simmel animation may look like this (an artist’s reconstruction). Image credit: Liz Little (modified with permission).

It is not surprising that ToM requires only sparse perceptual cues, since an efficient ToM offers an evolutionary advantage. Organisms that are better at judging when to cooperate and when to flee are more likely to survive and to reproduce. What may be surprising is that simple stories for children and cartoons like the one you just watched can help scientists reverse-engineer human thought.

Theory of Mind has its very own regions in the brain

From fMRI experiments with cartoons, such as a recent study in PLOS ONE, and stories, we know that ToM relies on several regions in the brain, which increase their consumption of oxygenated blood when people attribute thoughts and emotions to characters in a story:

Social perception develops gradually

The ability to reason about the beliefs and motivations of other people emerges in fragments during the first five years of life. Remarkably, rudimentary facial recognition is already present in newborns. Recognizing that an object is animate based on how it moves and looks develops before six months of age.

As an aside, our “life detector” is surprisingly simple. Research shows that the three main things you need to create the impression that an object is alive is to:

  • Make it move from a resting state,
  • Orient the axis of the object in the direction of its motion
  • And, optional but incredibly effective, a pair of eyes makes the illusion stronger

Puppeteers know and use these techniques to create the illusion of life with theater puppets. Look for these tactics next time you take your niece or nephew to a puppet theater!

More complex social abilities develop later. A six-to-ten-month-old infant can tell from a person’s behavior if a person’s actions is helping or hindering another person. A 14-month-old infant can understand behavior as caused by goal-directed actions. However, most children take about five years learning to recognize false beliefs, or, in other words, that people sometimes act on beliefs that differ from the actual state of the world.

 Reasoning about other peoples' mental states is fundamental to social life. Lucas van Leyden, The game of chess, 16th century. Public domain.
Reasoning about other peoples’ mental states is fundamental to social life. Lucas van Leyden, The game of chess, 16th century. Public domain.

A recent PLOS ONE paper examined how children younger than five years develop reasoning about false beliefs from naïve representations of falsity.

In the study, researchers presented children with game-play scenarios, where the experimenter hides a coin in one of two boxes and the child tries to find the coin. The experimenter gives the child prompts as to where the coin may be hidden. The study found that by having the experimenter change how the prompts are worded, two-year-old children can use negation to exclude alternatives (e.g. the coin is not in the red box) but not false assertions (e.g. the bear says that the coin is in the red box, but that is not true). In contrast, three-year-old children understand that assertions may be false and can successfully use the latter hint.

Moreover, four-year-old children can disregard a testimony described as mistaken (e.g. the bear says that the coin is in the red box, but he is mistaken). Thus, although children under five years are unable to recall or describe a false belief, they may act as though assertions and beliefs are false. The researchers suggest that children may fail to remember, interpret, and reject false assertions not because they lack the conceptual apparatus of falsity, but simply because young children have little experience with it. So, like any ability, the ability to discriminate what others think about the world from the actual state of the world may gradually come from experience, and experience takes time.

Now that you are armed with this scientific knowledge, you won’t be surprised if this year, your five-year-old niece or nephew declares that Santa does not exist or starts asking awkward questions which they didn’t yet ask last year. Contrary to popular belief, the notion that Santa may not be real does not come to children due to inadvertent exposure to the truth, but rather from the child’s newly acquired capacity for counterfactual thinking. Believing in Santa is a normal part of development, but like many good things it eventually comes to an end. While a three-year-old child is more likely to trust the assertions of others, a five-year-old is more equipped to recognize and articulate falsity in the beliefs of others.  In the long run, the ability to understand the thoughts and motivations of other people is an indispensable life skill. Indeed, it is the best fifth Christmas present for which one could wish.


Jenkins, Adrianna C., et al. “The Neural Bases of Directed and Spontaneous Mental State Attributions to Group Agents.” (2014): e105341

J. K. Hamlin, KarenWynn, and Paul Bloom. “Social evaluation by preverbal infants.” Nature, 450:557-560, 2007

Heider, F., & Simmel, M. (1944) “An experimental study in apparent behavior.” The American Journal of Psychology, 57, 243-259.

Koster-Hale, Jorie, and Rebecca Saxe. “Theory of mind: a neural prediction problem.” Neuron 79.5 (2013): 836-848.

Mascaro, Olivier, and Olivier Morin. “Epistemology for Beginners: Two-to Five-Year-Old Children’s Representation of Falsity.” PLOS ONE 10.10 (2015): e0140658.

Otti, Alexander, Afra M. Wohlschlaeger, and Michael Noll-Hussong. “Is the medial prefrontal cortex necessary for Theory of Mind?.” PLOS ONE 10.8 (2015): e0135912.

Saxe, Rebecca, Susan Carey, and Nancy Kanwisher. “Understanding other minds: linking developmental psychology and functional neuroimaging.” Annu. Rev. Psychol. 55 (2004): 87-124.


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