Measuring beliefs in centimeters: private knowledge biases preschoolers' and adults' representation of others' beliefs.

A novel task, using a continuous spatial layout, was created to investigate the degree to which (in centimeters) 3-year-old children's (N = 63), 5-year-old children's (N = 60), and adults' (N = 60) own privileged knowledge of the location of an object biased their representation of a protagonist's false belief about the object's location. At all ages, participants' knowledge of the object's actual location biased their search estimates, independent of the attentional or memory demands of the task. Children's degree of bias correlated with their performance on a classic change-of-location false belief task, controlling for age. This task is a novel tool for providing a quantitative measurement of the degree to which self-knowledge can bias estimates of others' beliefs.