Syntactic Structure Processing in the Brain while Listening
This work addresses how different syntactic parsing methods map to brain regions during listening, providing insights for neuroscience and computational linguistics, but it is incremental as it builds on prior brain encoding models.
The study investigated the predictive power of constituency and dependency syntactic parsing embeddings for brain activity during listening, finding that constituency parsers explain activations in the temporal lobe and middle-frontal gyrus, while dependency parsers are better for the angular gyrus and posterior cingulate cortex, with syntactic methods adding variance beyond semantic signals from BERT.
Syntactic parsing is the task of assigning a syntactic structure to a sentence. There are two popular syntactic parsing methods: constituency and dependency parsing. Recent works have used syntactic embeddings based on constituency trees, incremental top-down parsing, and other word syntactic features for brain activity prediction given the text stimuli to study how the syntax structure is represented in the brain's language network. However, the effectiveness of dependency parse trees or the relative predictive power of the various syntax parsers across brain areas, especially for the listening task, is yet unexplored. In this study, we investigate the predictive power of the brain encoding models in three settings: (i) individual performance of the constituency and dependency syntactic parsing based embedding methods, (ii) efficacy of these syntactic parsing based embedding methods when controlling for basic syntactic signals, (iii) relative effectiveness of each of the syntactic embedding methods when controlling for the other. Further, we explore the relative importance of syntactic information (from these syntactic embedding methods) versus semantic information using BERT embeddings. We find that constituency parsers help explain activations in the temporal lobe and middle-frontal gyrus, while dependency parsers better encode syntactic structure in the angular gyrus and posterior cingulate cortex. Although semantic signals from BERT are more effective compared to any of the syntactic features or embedding methods, syntactic embedding methods explain additional variance for a few brain regions.