Who can communicate with whom? Language experience affects infants' evaluation of others as monolingual or multilingual.

Adults recognize that people can understand more than one language. However, it is unclear whether infants assume other people understand one or multiple languages. We examined whether monolingual and bilingual 20-month-olds expect an unfamiliar person to understand one or more than one language. Two speakers told a listener the location of a hidden object using either the same or two different languages. When different languages were spoken, monolinguals looked longer when the listener searched correctly, bilinguals did not; when the same language was spoken, both groups looked longer for incorrect searches. Infants rely on their prior language experience when evaluating the language abilities of a novel individual. Monolingual infants assume others can understand only one language, although not necessarily the infants' own; bilinguals do not. Infants' assumptions about which community of conventions people belong to may allow them to recognize effective communicative partners and thus opportunities to acquire language, knowledge, and culture.