The language of space: Where is this and where is that?

Abstract

Introduction and Objective: The hypothesis that language-cognitive system interactions play a role in understanding domain-specific semantic terms is supported by a few neurophysiological studies, mainly on the motor cortex. Our goal was to assess if visuospatial coding affects the semantic comprehension of space-related words differently for peripersonal and extrapersonal space, and the causal role of the posterior parietal cortex (PPC).Methods: Utilizing Unity3D and Oculus Rift S, a virtual reality setup displayed 3D words at peripersonal (60 cm) and extrapersonal (120 cm) space. Participants performed a lexical decision task distinguishing between pseudowords and a near ("this") or far ("that") semantically related words, under conditions with and without tool use. The experiment included baseline, cathodal tDCS over the right PPC, and dual tDCS sessions, measuring Vocal Reaction Times (RTs) and analysing them with repeated measures ANOVA to assess semantic distance effects under various conditions.Results: Baseline conditions showed significantly faster RTs for near-semantically related words in peripersonal space. Tool use decreased RTs for near-semantically related words in extrapersonal space. Cathodal tDCS can revert this latter phenomenon by increasing RTs for near-semantically related words when a tool is used. Dual tDCS globally reduced RTs, regardless for position, semantics, and tool.Discussion and Conclusions: The findings suggest visuospatial coding influences near and far semantic processing, with or without a virtual tool, and highlight a causal role for right PPC. The overall RT reduction following dual tDCS could be due to enhanced reading performance from increased left-PPC excitability and decreased inter-hemispheric inhibition from right-PPC.