To understand mechanisms of early language acquisition, it is important to know whether the child's brain acts in an adult-like manner when processing words in meaningful contexts. The N400, a negative component in the event-related potential (ERP) of adults, is a sensitive index of semantic processing reflecting neural mechanisms of semantic integration into context. In the present study, we investigated whether the mechanisms indexed by the N400 are already working during early language acquisition. While 19-month-olds were looking at sequentially presented pictures, they were acoustically presented with words that were either congruous or incongruous to the picture content. The ERP averaged across the group of 55 children revealed an N400-like semantic incongruity effect in addition to an early phonological–lexical priming effect. The results suggest that both lexical expectations facilitating early phonological processing and mechanisms of semantic priming facilitating integration into semantic context are already present in 19-month-olds. The child's specific comprehension abilities are reflected in strength, latency, and hemispheric differences of the semantic incongruity effect. Spatio-temporal differences in that effect, thus, indicate changes in the organization of brain activity correlated with the child's behavioral development.

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