Accentuate or repeat? Brain signatures of developmental periods in infant word recognition

Language acquisition has long been discussed as an interaction between biological preconditions and environmental input. This general interaction seems particularly salient in lexical acquisition, where infants are already able to detect unknown words in sentences at 7 months of age, guided by phonological and statistical information in the speech input. While this information results from the linguistic structure of a given language, infants also exploit situational information, such as speakers' additional word accentuation and word repetition. The current study investigated the developmental trajectory of infants' sensitivity to these two situational input cues in word recognition. Testing infants at 6, 9, and 12 months of age, we hypothesized that different age groups are differentially sensitive to accentuation and repetition. In a familiarization-test paradigm, event-related brain potentials (ERPs) revealed age-related differences in infants' word recognition as a function of situational input cues: at 6 months infants only recognized previously accentuated words, at 9 months both accentuation and repetition played a role, while at 12 months only repetition was effective. These developmental changes are suggested to result from infants' advancing linguistic experience and parallel auditory cortex maturation. Our data indicate very narrow and specific input-sensitive periods in infant word recognition, with accentuation being effective prior to repetition.