Disentangling Lexical and Semantic Rhythmicity from the Construction of Hierarchical Structures: Effects on the EEG Signal

Neural entrainment to language has been linked to both hierarchical syntactic processing and to lexical representations. A pioneering study from Ding et al. (2016), who implemented the frequency-tagging paradigm using auditory stimuli presented at a fixed rhythm, examined the phenomenon and showed that their results were consistent with the hypothesis that neural oscillations entrain to hierarchical syntactic structures. Their conclusions were challenged by Frank and Yang (2018), who showed that neural oscillations could entrain to simple lexical representations without the need for syntax. Our study is based on the paradigm from Ding et al. (2016), and we modified it in two ways: (1) by using a rhythmic syllable-by-syllable presentation of multisyllabic words that vary in phrase and sentence structure, and (2) with the use of visual stimuli (in Italian) instead of auditory stimuli. This approach allowed us to examine neural entrainment in written language, while differentiating the role of the of more posterior and ventral language processing areas (e.g. Visual Word Form Area) from the middle and inferior temporal gyrus, which is the area related to syntactic processing. Furthermore, the Italian language allows for a more diverse sentence structure due to its complexity and flexibility. Our research implemented the use of Electroencephalography (EEG), and we examined neural activity in response to a set of extremely regular copular sentences and a set of sentences that varied in structure and that maintained regularity only at the level of the phrase and the sentence. The results offer a new perspective on the role of neural entrainment in language processing and contribute to the ongoing research on the roles of syntax and lexical representation in neural oscillations.