Theory of mind (ToM) is the ability to understand that others have mental states — beliefs, desires, intentions, and knowledge — that may differ from one's own and that guide their behavior. This capacity is fundamental to social cognition, enabling us to predict, explain, and influence others' actions by reasoning about their psychological states rather than just their observable behavior.
The False Belief Task
The hallmark test of ToM is the false belief task (Wimmer and Perner, 1983). In the standard version, a character (Sally) places a marble in a basket and leaves. Another character (Anne) moves the marble to a box. Children are asked where Sally will look for the marble when she returns. Children under about 4 years typically say Sally will look in the box (where the marble actually is), failing to represent Sally's false belief. Around age 4-5, children correctly predict that Sally will look in the basket (where she believes the marble is), demonstrating understanding of false belief.
Neural Basis
Theory of mind engages a specific brain network including the temporoparietal junction (TPJ), medial prefrontal cortex (mPFC), posterior superior temporal sulcus (pSTS), and precuneus. This "mentalizing network" is activated when people think about others' thoughts, beliefs, and intentions, and is distinct from networks involved in other social processes like empathy (which involves the anterior insula and anterior cingulate).
Simon Baron-Cohen, Alan Leslie, and Uta Frith (1985) proposed that autism spectrum disorder involves a core deficit in theory of mind — "mindblindness." Children with autism show delayed or impaired false belief understanding, difficulty interpreting others' mental states from behavior and facial expressions, and reduced spontaneous attribution of mental states. While the mindblindness theory does not account for all features of autism, ToM deficits remain a central component of the condition.