Knowing That You Don't Know What I Know
Theory of mind is the capacity to understand other people by attributing mental states to them. It includes grasping that someone else's beliefs, desires, intentions, emotions and thoughts may be completely different from your own.
That sounds obvious until you try to do without it. We use theory of mind constantly when we analyse, judge and infer other people's behaviour, and possessing a working one is crucial for success in everyday social interaction.
It is closely related to empathy, but not the same thing. Empathy is usually described as emotional perspective-taking, putting yourself in someone else's shoes and feeling what they feel. Theory of mind is cognitive perspective-taking: working out what someone else knows, wants or believes, whether or not you share the feeling.
Why It Is Called a Theory
The name is precise, and it is worth unpacking. It is called a theory because the only thing you ever directly observe is the other person's behaviour: their statements, their expressions, their actions.
Nobody has direct access to another mind. Its existence and its nature have to be inferred. We simply assume other people have minds like our own, an assumption built on three reciprocal social foundations: joint attention, the functional use of language, and understanding other people's emotions and actions.
So every social interaction rests on a working hypothesis about an unobservable thing. Attributing mental states to others, and treating them as the causes of behaviour, means being able to conceive of the mind as a generator of representations. Theory of mind appears to be an innate potential in humans that still needs years of social experience to develop fully, and different people end up with more or less effective versions of it.
The False-Belief Test
The central milestone is the ability to attribute a false belief: to understand that other people can believe things that are not true.
Numerous versions of the false-belief task have been developed, all based on the original designed by Wimmer and Perner in 1983. The structure is always the same. A child watches someone form a belief about where an object is, then watches that object get moved while the person is away, and is asked where the person will look for it. Younger children say where the object actually is, because they cannot yet separate their own knowledge from someone else's.
Five key aspects develop in sequence between the ages of three and five: diverse desires, diverse beliefs, knowledge access, false beliefs, and hidden emotions. Remarkably, the order appears to hold across cultures. Studies of children in Canada, India, Peru, Samoa and Thailand found they all pass the false-belief task at around the same age.
A Question First Asked About Chimpanzees
The concept did not begin with children at all. Theory of mind was first conceptualised by researchers evaluating whether animals have one.
The field exploded after a single paper: Premack and Guy Woodruff's 1978 article titled "Does the chimpanzee have a theory of mind?". Research in humans and animals, adults and children, has grown rapidly ever since.
Today researchers investigate what affects the capacity in people, including drug and alcohol consumption, language development, cognitive delays, age and culture. Social neuroscience has joined in by imaging brains while people work out someone else's intentions or beliefs.
The animal question is harder than it looks, and for the same reason the whole field is called a theory. You cannot ask a chimpanzee what it believes. You can only set up a situation where an animal that understands another's knowledge would behave differently from one that does not, then watch which way it goes.
Where It Lives in the Brain
Neuroimaging has linked theory of mind tasks to a specific set of brain regions: the medial prefrontal cortex, the posterior superior temporal sulcus, the precuneus and the amygdala.
The evidence from injury points the same way. Patients with damage to the frontal lobe or to the temporoparietal junction find some theory of mind tasks difficult. In children, the capacity develops as the prefrontal cortex develops, which fits the timeline of those milestones between three and five.
Researchers have also proposed that deficits in theory of mind may occur in people with autism, anorexia nervosa, schizophrenia, dysphoria, addiction, and brain damage caused by the toxic effects of alcohol. An alternative account comes from operant psychology, which offers a functional explanation of both perspective-taking and empathy through research on derived relational responding.
