Cortical tracking of constituent structure in language acquisition

Linguistic units are organized at multiple levels: words combine to form phrases, which combine to form sentences. Ding, Melloni, Zhang, Tian, and Poeppel (2016) discovered that the brain tracks units at each level of hierarchical structure simultaneously. Such tracking requires knowledge of how words and phrases are structurally related. Here we asked how neural tracking emerges as knowledge of phrase structure is acquired. We recorded electrophysiological (MEG) data while adults listened to a miniature language with distributional cues to phrase structure or to a control language which lacked the crucial distributional cues. Neural tracking of phrases developed rapidly, only in the condition in which participants formed mental representations of phrase structure as measured behaviorally. These results illuminate the mechanisms through which abstract mental representations are acquired and processed by the brain.