Out now in the Journal of Neuroscience, Junyuan Zhao develops an approach to decoding the category features of phrases from EEG data. He goes on to demonstrate that the neural representation of the phrase head is reactivated at phrasal boundaries and also that such reactivation is does not appear to be modulated by conceptual similarity or word predictability.
The experimental design and set of analyses, including a host of careful controls, represent exciting path forward in extending neural decoding methods to complex syntactic representations. Read on for more!
Zhao, J., Gao, R., & Brennan, J.R. (2025). Decoding the Neural Dynamics of Headed Syntactic Structure Building. Journal of Neuroscience.
doi: 10.1523/JNEUROSCI.2126-24.2025
Abstract:
The brain builds hierarchical phrases during language comprehension; however, the representational details and dynamics of the phrase-building process remain underspecified. This study directly probes whether the neural code of verb phrases involves reactivating the syntactic property of a key subcomponent (the “head” verb). To this end, we train a part-of-speech sliding-window neural decoder (verb vs. adverb) on EEG signals recorded while 30 participants (17 females) read sentences in a controlled experiment. The decoder reaches above-chance performance that is spatiotemporally consistent and generalizes to unseen data across sentence positions. Appling the decoder to held-out data yields predicted activation levels for the verbal “head” of a verb phrase at a distant non-head word (adverb); the critical adverb appeared either at the end of a verb phrase or at a sequentially and lexically matched position with no verb phrase boundary. There is stronger verb activation beginning at ∼600 milliseconds at the critical adverb when it appears at a verb phrase boundary; this effect is not modulated by the strength of conceptual association between the two subcomponents in the verb phrase nor does it reflect word predictability. Time-locked analyses additionally reveal a negativity waveform component and increased beta-delta inter-trial phase coherence, both previously linked to linguistic composition, in a similar time window. With a novel application of neural decoding, our findings delineate the dynamics by which the brain encodes phrasal representations by, in part, reactivating the representation of key subcomponents. We thus establish a link between cognitive accounts of phrasal representations and electrophysiological dynamics.