Testing for a Theory of Mind

• The development of a Theory of Mind on tests subjects is usually measured by their ability to attribute beliefs, and particularly false beliefs, to others. In a classic experiment, a boy doll puts a ball in a box and walks away. While he is gone another doll takes the ball, plays with it and puts it away in a basket. When the boy returns and wants to play with the ball, the children being tested are asked where he will look for it. Three to four-year-old children tend to assume the doll will look into the basket, arguably because they have a model of the physical world but lack a model of the doll's mind. Children over five, however, consistently guess that the doll will look for the ball in the box: they understand what is going on in the doll's mind.
  
  

Evidence for the Relationship of a Theory of Mind and Language Development

• General language ability and verbal memory have been found to be significant predictors of false belief understanding. Children consistently fail false belief tasks if they have not reached a certain level of linguistic ability. Thus, performance in false belief tests increases sharply around the five years of age, a time where there is also a major period of language acquisition. The observation is reinforced by studies of deaf children whose language development is delayed. Their tests frequently show failure to understand false beliefs, although their nonverbal intelligence and social adjustment are within normal levels.
  
  

Possible Correlation Mechanisms

• This correlation between language development and theory of mind can be explained by invoking the Sapir-Whorf theory. Language shapes thought, and some abstract thoughts just cannot be had unless the right words are present in the subject's vocabulary (in the case of Theory of Mind, those crucial words would be "thinks", "believes", "assumes" and so on). The correlation between language development and a theory of mind can also be explained by evolutionary caused. Children in the evolutionary past, like children today, had to learn their language through social-interactive learning, imitation and practice, relying on Theory of Mind skills. Without said skills, only a limited proto-language seems feasible. Thus, language and theory of mind could have induced a virtuous evolutionary cycle where an incipient Theory of Mind led to a full-fledged language that led to a more mature theory.
  
  

Related But Not Inseparable

• There is evidence, however, suggesting that language and Theory of Mind become more autonomous in later stages of development. For instance, adults who lose their language capabilities may retain their theory of mind skills, and at least some autistic children can catch up with their language skills in later years without overcoming their deficiencies in Theory of Mind.
  
  

Theory of Mind and Primates

• Given the very apparent correlation between language and theory of mind, it may seem peculiar that the term was first used in relation to non-linguistic creatures, more specifically chimpanzees. The results of the study documented in "Does the Chimpanzee Have a Theory of Mind?", published in 1978 seemed to suggest that other primates could have representations of the mental and psychological states of others. While the results are still in dispute and contemporary experiments are inconclusive, the fact that primates seem to have both an incipient grasp of language and a grasp of Theory of Mind skills seems to indicate that both are indeed related.