Hierarchical processing in seven-month-old infants

Hierarchical structures are crucial to many aspects of cognitive processing and especially for language. However, there still is little experimental support for the ability of infants to learn such structures. Here, we show that, with structures simple enough to be processed by various animals, seven-month-old infants seem to learn hierarchical relations. Infants were presented with an artificial language composed of "sentences" made of three-syllable "words." The syllables within words conformed to repetition patterns based on syllable tokens involving either adjacent repetitions (e.g., dubaba) or nonadjacent repetitions (e.g., dubadu). Importantly, the sequence of word structures in each sentence conformed to repetition patterns based on word types (e.g., aba-abb-abb). Infants learned this repetition pattern of repetition patterns and thus likely a hierarchical pattern based on repetitions, but only when the repeated word structure was based on adjacent repetitions. While our results leave open the question of which exact sentence-level pattern infants learned, they suggest that infants embedded the word-level patterns into a higher-level pattern and thus seemed to acquire a hierarchically embedded pattern.