An important part of human development is being able to develop the skills to relate and interact with other people.  Theory of mind is defined as the ability to figure out what another person might believe and predict others' behaviour by inferring a person's motivation. Some argue that this skill develops by interacting with the environment – that is, we develop schema as we interact with others that then help us to predict their behavior and better understand them.  This approach is known as theory theory. Others argue that we are “biologically preprogrammed” to understand other people.  This is known as simulation theory – that is, we use our own mind as a model for understanding the minds of others. Simulation theory has been supported by the discovery of mirror neurons.

Repacholi and Gopnik carried out a study to see at what age children are able to understand that other people may have different thinking than theirs. Children aged 14 and 18 months were given two bowls of snacks.  One bowl had crackers and the other had raw broccoli. The researcher tried the crackers and made a face of disgust.  She then ate the broccoli and showed that she loved it!  The researcher then asked the child to give them something to eat. The 14-month-olds gave the researchers the food that they liked (crackers) but 18-month-olds correctly gave her broccoli. This shows that children develop the belief-desire stage before 2 years old.  That is – they understand that others have different beliefs and desires than they do.

The study shows some of the difficulties of studying theory of mind.  First, the research is cross-sectional. The children only engaged in the task once and did not show development over time. In fact, Ruffman et al (2017) replicated the study and found that only 1/3 of the children showed this level of development by 18 months.  In addition, there are only two options here – so the children had a 50/50 chance of getting the correct answer. It is not possible to know why the children made the choices they did – and it may not be because they understood what the researcher actually liked.  In research with young children, it is often the problem that children cannot explain their choices or behaviour to the researcher.  

Another stage of the development of theory of mind is when children understand that others may have false beliefs. Baron-Cohen gave the Sally-Anne task to children to see what age would be able to understand the following problem:  Sally put her marble in a basket.  When Sally goes away, Anne put her marble in her box.  When Sally comes back, where will she look for the marble?  He found that children under 4 assumed that if they knew where the marble was, then Sally must know too.  It was children over four who understood that she would mistakenly look in the basket. 

There are some criticisms of the Sally-Anne test – mostly that the language used may actually be the reason for the results.  In a replication of the study, a researcher asked, “Where did Sally first look for her marble?”  With the addition of this word, 70% of the three-year-olds were able to answer correctly.

Biologists argue that the development of empathy goes hand in hand with our brain development.  Iacoboni accidentally discovered mirror neurons while studying brain activity in monkeys. He found that when a monkey watched a human grasp something, neurons in their brains fired as if they were grasping the object themselves. This is why when we watch someone get hit in a movie, we often react as if we are getting hit ourselves.  These neurons may play a key role in the development of theory of mind.

Carr carried out a study where he had participants look at human faces while in an fMRI. He wanted to see if simply looking at the emotion expressed on someone’s face would stimulate similar regions of the brain. The findings were that the same areas of the brain activated in when a participant imitated the facial expression and when they just observed the facial expression. In addition, seeing a happy face activated pleasure centers in the brain.

Researchers believe that mirror neurons have evolved to make us capable of understanding others. This may be some of the first biological evidence for the development of theory of mind and empathy. However, the research by Carr was done on adults and this does not address the question of whether children develop these neurons over time. It is possible that mirror neuron development is part of normal brain development as we know that a child's brain continues to develop over time.  In addition, the age of 3 to 4 seems to be an important developmental goalpost for several brain developments, for example, the hippocampus.

There are limitations to the study of the development of theory of mind in young children.  Language often serves as a confounding variable, especially when tasks become more complex.  In addition, small children cannot explain why they make the choices they do. There is also an assumption that theory of mind develops in specific stages that are universal. Stage theories can be problematic in that often children do not develop in the same linear manner across all cultures.  Finally, the argument that we develop theory of mind either by interacting with the environment as Piaget and Vygotsky argued or by a predetermined biological development may be incorrect.  In fact, it may be that we develop both biologically and through interacting with the environment – and not an either/or situation.