Temporal dynamics of syntax and semantics during minimal hierarchical structure processing

The ability to construct hierarchical structures through syntactic Merge and semantic processes is a cornerstone of human language. Despite decades of debate over serial vs. parallel interaction processing models, the temporal dynamics underlying the interaction between syntax and semantics during even minimal hierarchical structure construction remain unclear. To address this, we employed a 2 (Sequence rules: hierarchical vs. linear) × 2 (Semantics: associated vs. unassociated) design in verb-noun sequences to disentangle syntax and semantics processing. We recorded the EEG data while 48 Chinese speakers read two words successively under a one-word probe task. The results from ERP and multivariate pattern classification analysis demonstrated (1) early syntactic Merge processing, and (2) the progressively intensifying interplay between syntax and semantics, where syntactic processing establishes structure stably from the early-stage while semantic processing incrementally intensifies over time. These findings challenge traditional serial and parallel processing models by uncovering simultaneous yet distinct temporal trajectory of syntactic and semantic processing. By bridging principles of the Minimalist Program with empirical evidence, we propose a dynamic parallel interaction processing model, highlighting the distinct but interdependent roles of syntax and semantics, with syntax serving as a foundational scaffold and semantics contributing the depth and variability needed for meaningful communication.