From perceiving words to reading: Neural multivariate representations of sublexical vs. lexico-semantic processing during word-reading

While the neural underpinnings of semantic cognition have been extensively studied, the brain mechanisms that allow the extraction of meaning from the initially perceptual visual linguistic input are less understood. These mechanisms have typically been explored through the analysis of psycholinguistic properties that reflect key aspects of semantic processing (e.g., word frequency, familiarity or concreteness), and more recently, through natural language processing (NLP) models. However, both approaches lack a direct comparison of sublexical (i.e., phonological and orthographic) and lexico-semantic aspects of words, with NLP models. Understanding how sublexical and lexico-semantic systems interact and/or overlap is a current challenge in the field of neurobiology of language. In this fMRI study, 30 participants performed a lexical decision task in the MRI, where all aforementioned sublexical and lexico-semantic properties were carefully controlled. The resulting models reflected either sublexical, semantic, or NLP (word vector) relations, which were compared to multivariate brain patterns in representational similarity analysis. Our findings reveal that sublexical and lexico-semantic representations recruit different areas of the left inferior frontal gyrus (IFG) and ventral occipitotemporal cortex (vOTC). The anterior IFG and vOTC represented semantic models, while regions posterior to the IFG, like supplementary motor area (SMA), or to the vOTC, like areas V3-V4, showed representations of sublexical models. Importantly, both semantic and NLP models converged in semantic hubs, including the inferior anterior temporal lobe (ATL), parahippocampal gyrus, or anterior IFG. The implications of these results are discussed in line with the most recent neuroscientific evidence.