Previous research suggests that older children expect members of social groups to share characteristics. Here, we examined whether 20-month-old infants demonstrate similar stereotype-based reasoning by expecting members of a social group to share preferences. In Experiment 1, infants were first introduced to two arbitrary social groups that were defined by matching costumes and labels. In the next three trials, infants saw a member of one of the social groups (a Topid) choose between two foods. In the test trial, infants saw either a member of the same social group (another Topid) or a member of a different social group (a Brinko) choose the same food as the previous Topid, or a different food. Infants looked reliably longer when members of the same social group picked different foods compared to when they picked the same foods. In contrast, infants who saw a member of a different group in the test trial looked equally regardless of which food the individual selected. These results suggest that infants expected members of the same, but not different, social groups to share preferences.
Experiment 2 replicated the findings from the same-group condition and extended them to social groups that were labeled with adjectives instead of nouns, which suggests that noun labels were not necessary for infants to form stereotyped beliefs about the groups. These findings provide new evidence that infants as young as 20 months demonstrate stereotype-based reasoning about novel social groups.