Training a Bayesian: Three-and-a-half-year-olds’ Reasoning about Ambiguous Evidence

Previous work has demonstrated the importance of both naïve theories and statistical evidence to children’s causal reasoning. In particular, four-year-olds can use statistical evidence to update their beliefs. However, the story is more complex for three-year-olds. Although three-and-a-half-yearolds perform as well as four-year-olds when statistical evidence is theory-neutral, several studies suggest that they do not learn from statistical evidence when a statistically likely cause is inconsistent with their prior beliefs (e.g., Schulz et al., 2007). There are at least two possible explanations for younger children’s failure to use statistical data to update their beliefs: one (the Information Processing account) suggests that younger children have a fragile ability to reason about statistical evidence; the other (a Prior Knowledge account) suggests that in some domains, younger children have stronger prior beliefs and thus require more evidence before belief revision is rational. To distinguish these accounts, we conducted a two-week training study with three-and-a-halfyear-olds. Children participated in an Information Processing Training condition, a Prior Belief Training condition, or a Control condition. Relative to the Control condition, children in the Prior Belief Training condition, but not children in the Information Processing Training condition showed an overall improvement in their ability to reason about theory-violating evidence. This suggests that at least some developmental differences in statistical reasoning tasks may be due to younger children’s stronger prior beliefs.