Developmental changes in consistency of preferential feeling for peers and objects around age four.

When do young children come to have an individual mental image of each peer? Forming a stable impression of each person requires maturation of at least two cognitive abilities, inferring the other's mind and episodic memory. According to past studies, the critical period for both these abilities is around age four. Thus, it was hypothesized that the child begins to form a consistent mental image of each peer at or after age four. To test this hypothesis, the temporal consistency of preference for peers was examined in 3-, 4-, and 5-yr.-olds. Each subject was asked "Who do you like better than others in this class?" once a week for three times (Study 1). The results indicated that most of the 3-yr.-olds answered different names as their favorite friends or nonsense things inconsistently week by week, whereas older children tended to answer the same names across weeks. However, changing the question to "Which object do you like best of these alternatives?" dramatically changed the response pattern (Study 2): preferences among nonhuman objects (playthings) were temporally consistent even for 3-yr.-olds. These results indicate that children before age four do have a temporally consistent feeling toward general objects but do not have a consistent firm feeling about personal relationships among peers. The results are discussed in relation to the critical developmental changes about age 4 in other cognitive abilities.