Young children's understanding of desire formation.

Two studies examined preschoolers' appreciation of how mental states arise. In Study 1, children aged 3 to 5 (24 at each age) better understood perception-generated beliefs (e.g., that looking in a certain location generates a belief about the location's content) and attitude-generated desires (e.g., that positive experiences with an activity generate a desire to partake of the activity again) than physiology-generated desires (e.g., that not eating for a long time generates a desire for food). In Study 2, 4- and 5-year-olds (48 at each age) better understood the effects of quantity of experience (e.g., eating a lot vs. a little) than of time of experience (eating just now vs. a long time ago) on physiological states and desires. The findings suggest that whether children reason in more advanced fashion about desires or beliefs depends on which aspects of these mental states are considered.