As humans, we don't just belong to a community of bodies. To borrow a lovely phrase from developmental psychologist Katherine Nelson, we also belong to a "community of minds."
We engage with each other as individuals with thoughts and with feelings and beliefs. When I reach for the chocolate, you don't just see a moving arm; you see an intentional action that can be explained by appeal to my desire for chocolate. To predict which gift my partner will like best, I consider his preferences and beliefs — the contents of his mind.
The ability to infer and reason about people's mental states is sometimes referred to as "theory of mind," or more charmingly, as "mind reading." It's something most of us do pretty well, while falling far short of perfection. Misunderstandings happen all the time, and it can be hard to adopt the perspective of a person with fundamentally different beliefs, especially about things we hold dear — religion, politics, morality.
The challenge of "reading" other minds begins in early childhood, as young children start to make sense of the social and physical world around them. But the challenge for young children is much greater than ours: It's not only a matter of figuring out the contents of particular minds, but of figuring out the underlying mechanics. They need to appreciate that other people can have desires that depart from their own. They need to understand that people's behavior isn't simply governed by reality, but by their beliefs about reality. If I prefer chocolate to lollipops, for example, I'll reach for the chocolate, even if you would prefer the lollipops. If I believe the chocolate is in the cupboard (and not in the refrigerator), I'll look for it in the cupboard, even if I'm wrong.
At this point, hundreds of studies have investigated how it is that children develop a theory of mind. When do different abilities emerge? Is there variation across cultures? Are some children better mind readers than others? If so, why?
Among the most contentious questions is how mind-reading ability develops at all. Does theory of mind emerge through a process of maturation, more or less like puberty? Or is it something children learn through their experience in the world?
These questions don't have easy answers, but three decades of research offer new opportunities for tackling them in powerful and systematic ways. Rather than a piecemeal approach, inching forward one study at a time, researchers are using the tools of meta-analysis to synthesize findings across dozens of studies that have already been conducted. By looking at multiple studies in aggregate, researchers can get a better sense for which findings are reliable and robust, whether effects are large or small, and whether multiple factors interact to generate a given finding.
A paper forthcoming in the journal Child Development does exactly this. It aggregates the results of more than 93 data sets to identify whether the features of the family environments of 3- to 7-year-old children predict the emergence of one crucial aspect of theory of mind: an understanding that other people can have false beliefs. False belief understanding is among the most studied milestones in theory of mind development because it signals the emergence of an ability to represent beliefs as distinct from reality.
The paper, authored by Rory Devine and Claire Hughes, digs into the relationship between false belief understanding and four features of a child's home environment: parental socioeconomic status, number of siblings in the home, the extent to which parents use mental state terms in talking with their child, and the parents' "mind-mindedness" — that is, their tendency to view their child as a psychological agent, as reflected in the way they talk to or about their child.
Despite variation across individual studies, in aggregate the studies suggest modest but statistically significant associations between all four of these factors and a child's false belief understanding. Specifically, children develop this ability earlier when they come from families with higher SES, have more siblings in the home, and have parents who use more mental state terms and score higher on mind-mindedness. Moreover, these associations remain when differences in children's verbal abilities are taken into account, suggesting a specific association between these family variables and false belief understanding, rather than a more diffuse effect via verbal reasoning or intelligence.
The meta-analysis also allowed the researchers to test more nuanced hypotheses by looking for patterns across studies. For instance, they found that the theory of mind benefit associated with siblings was greater when siblings were similar in age to the child, as opposed to being older. This suggests that the sibling advantage isn't merely a consequence of growing up in a family environment with a greater number of competent mind readers, but that there might be something about particular kinds of sibling interactions that fosters speedier development. Another finding was that the effects of socioeconomic status couldn't be explained by the other variables that were measured — it wasn't the case, for instance, that the children of higher SES-parents did better only because their parents engaged in more mental state talk or were more mind-minded.
Returning to questions of nature versus nurture, the analyses point toward an important role for social environment — and hence experience — in developing an accurate theory of mind. In particular, they suggest that certain social experiences and linguistic input can influence when children learn that others have beliefs that can differ from reality.
On the other hand, the studies didn't control for genetic effects within families. Most children were related to their parents biologically, so associations between parental behavior and children's learning could instead reflect overlapping genes. Because the analyses were correlational, the associations could also arise from common causal factors other than shared genes. For instance, features of parents' and children's environments could influence both aspects of family environment and children's developing theory of mind.
Finally, it's worth repeating that the associations — while statistically significant — were modest in size. That leaves room for a host of other factors in explaining variation in children's developing theories of mind.
These caveats aside, the findings support a growing body of work that points to the importance of social learning in early childhood. The paper also highlights some of the strengths and limitations of meta-analyses. Such analyses are no substitute for additional research, but they can summarize and clarify what we do and don't already know, supporting tentative conclusions with greater confidence while guiding novel research.
Theory of mind isn't only important to children — it's important throughout our lives, affecting how we relate to each other and perhaps even how we relate to ourselves. That's why it's important to understanding how children come to join the community of minds, and how we earn membership ourselves.
Tania Lombrozo is a psychology professor at the University of California, Berkeley. She writes about psychology, cognitive science and philosophy, with occasional forays into parenting and veganism. You can keep up with more of what she is thinking on Twitter: @TaniaLombrozo