Wimmer and Perner (1983) proposed the so-called 'false-belief test', which examines human children's ToM. (The need for testing the 'false-belief' was originally claimed by the philosopher Dan Dennet, as a comment on the 1978 paper by Premach and Woodruff. About their chimpanzee experiments, see the previous post on this blog). The test should have the following formal paradigm.
[T]he subject is aware that he/she and another person observe a certain state of affairs x. Then, in the absense of the other person the subject witnesses an unexpected change in the state of affairs from x to y. The subject now knows that y is the case and also knows the other person still believes that x is the case.
[Wimmer, H. & Perner, J. (1983) Beliefs about Beliefs: Representation and constraining function of wrong beliefs in young children's understanding of deception. Cognition, 13:103-128, p.106]
Based on this paradigm, Wimmer and Perner constructed the well-known 'chocolate task';
[A] story character, Maxi, puts chocolate into a cupboard x. In his absence his mother displaces the chocolate from x into cupboard y. Subjects have to indicate the box where Maxi will look for the chocolate when he returns. Only when they are able to represent Maxi's wrong belief ('Chocolate is in x') apart from what they themselves know to be the case ('Chocolate is in y') will they be able to point correctly to box x. This procedure tests whether subjects have an explicit and definite representation of the other's wrong belief.
The result is enough interesting (and also well-known) that none of the 3 to 4 years old children pointed 'correctly' to the cupboard x. 57% of 4 to 6 years old, and 86% of 6 to 9 years old children pointed 'correctly' to the cupboard x.
[i}t seems, therefore, that the emergence of children's ability to understand another person's beliefs and how this person will react on the basis of these beliefs...seems to emerge within the period of 4 to 6 years.
I agree with their conclusion. The theory of mind is formed in children after (or around) being 4 years. This fact is well examined in many other experiments.
But now, we come to one simple question. If the children under 4 years of age don't have the theory of mind, can't they understand the other person or predict her/his behavior at all? After being 4 years old, they suddenly start to understand the others? If the theory of mind is the only way to understand the others, none of us can understand the others before the birthday party of 4 years old. It sounds so funny, doesn't it?