Decoding the temporal dynamics of numerical semantics: Early cardinal activation and the critical role of ordinal processing in spatial-numerical associations

Numbers are fundamental to human culture and technological advancement, influencing everything from basic measurement to complex computations. Despite their ubiquity, the cognitive processes underpinning numerical understanding, especially the spatial cognition of numbers, remain inadequately explored. Understanding these processes is crucial as they underpin our ability to learn and interact with our environment. This study utilizes a dual choice go/nogo paradigm integrated with event-related potential (ERP) technique and multivariate pattern analysis (MVPA) to examine the semantics processing mechanisms within spatial-numerical associations (SNAs), particularly focusing on the dynamic temporal characteristics of cardinal and ordinal semantics. The behavioral results revealed that the Spatial-Numerical Association of Response Codes (SNARC) effect was observed only in Experiment 1, whereas the ordinal position effect emerged consistently across both experiments, suggesting that SNAs primarily originate from sequential information constructed in working memory, challenging the traditional view that SNAs primarily arise from the spatial distribution of numerical quantity. Traditional ERP analysis did not detect significant motor preparation linked to numerical semantics. However, MVPA results indicated that cardinal semantics are processed prior to ordinal semantics. This temporal dissociation was observed with the decoding accuracy of cardinal semantics being significantly higher than the chance at 112 ms post-stimulus. In contrast, ordinal semantics processing emerged later (around 180-200 milliseconds), and combined analysis with response-related ERP component demonstrated that SNAs show closer associations with ordinal semantics. This research enriches our understanding of numerical cognition and provides new perspectives for exploring the complexity and diversity of SNAs.