Frith’s interest in theory of mind in autism began with a test to identify the age at which children can
reason about other people’s mindsets. She and her colleagues adapted the test using a story about two dolls,
Sally and Anne: Sally puts a marble into a basket and then leaves. Anne takes the marble out of the basket and places it inside a box. When Sally returns, the clinician asks the child where Sally will look for the marble. By age 4, most non-autistic children and those with Down syndrome can answer correctly that Sally will look in the basket, Frith and her colleagues found. The children understand that Sally holds a ‘false belief’: She does not know that Anne has moved her marble. By contrast, most of the autistic children they assessed, including those older than 4, could not answer correctly, suggesting the difficulty was somehow
specific to autism.