Sally-Anne psychological test

The Sally-Anne test is a classic psychological experiment designed to measure a child’s development of a Theory of Mind—the crucial cognitive milestone where a person realizes that other people have separate minds, beliefs, desires, and perspectives that can differ from their own. Developed by researchers Heinz Wimmer and Josef Perner in 1983, and later adapted by Simon Baron-Cohen, Alan M. Leslie, and Uta Frith in 1985 to study autism, the test presents children with a simple narrative using two dolls or puppets to observe how they track another person's knowledge state.

The test begins by introducing the child to two characters: Sally, who has a basket, and Anne, who has a box. Sally takes a marble (or sometimes a delicious cookie, as mentioned in the Vsauce video) and places it securely inside her basket. Sally then leaves the room to go for a walk. While Sally is away, Anne takes the marble out of the basket and hides it inside her own box. Sally then returns to the room, and the researcher asks the child the critical "Belief Question": "Where will Sally look for her marble?"

To pass the test, the child must separate their own knowledge from Sally's. A child who has successfully developed a Theory of Mind will answer that Sally will look in her basket. This demonstrates an understanding that Sally holds a false belief—she did not witness Anne move the marble, so her internal representation of reality is outdated. The child understands that what is true in the real world is different from what is true inside Sally's mind.

Conversely, young children under the age of four will almost always fail the test, confidently insisting that Sally will look in the box. Because the child saw Anne move the marble, they cannot decouple their own omniscient knowledge from Sally's limited perspective. They operate under the assumption that if they know where the object is, Sally must automatically know it too.

The Sally-Anne test remains a foundational tool in developmental psychology. Beyond tracking neurotypical development, the 1985 adaptation revealed that a significant majority of children on the autism spectrum struggled with the test, even when they possessed a higher mental age than neurotypical children who passed it. This finding helped researchers understand that certain developmental differences are directly tied to how the brain processes social cognition and models the internal states of others.