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.
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