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Exploring the dynamics underlying taxonomic and thematic semantic organization in picture naming

Poster C72 in Poster Session C, Friday, October 7, 10:15 am - 12:00 pm EDT, Millennium Hall

Mingjun Zhai¹, Chen Feng^2,3, Qingqing Qu^2,3, Simon Fischer-Baum; ¹Department of Psychological Sciences, Rice University, Houston, TX, ²Key Laboratory of Behavioral Science, Institute of Psychology, Chinese Academy of Sciences, Beijing, China, ³Department of Psychology, University of Chinese Academy of Sciences, Beijing, China

Semantic knowledge about concepts has been argued to be organized in different ways: based on shared features (taxonomic) or based on co-occurrence in common scenes and scenarios (thematic). The goal of the current study is to examine how flexibly different semantic systems can be engaged, with a focus on picture naming. Contemporary theories of semantic cognition, such as the dual-hub hypothesis (Mirmam et al., 2017) and the controlled semantic cognition (CSC) framework (Lambon Ralph et al., 2017) assume that task-context influences which semantic systems are engaged, though competing theories differ in details about how this flexibility operates, for example, whether both taxonomic and thematic systems are equally engaged or disengaged (dual-hub) or whether the taxonomic organization is the core structure of semantic knowledge, with thematic organization flexibly engaged only in appropriate task settings (CSC). Examining the effect of task demands and semantic contexts on which semantic systems are engaged can adjudicate competing theoretical accounts of semantic knowledge and resolve discrepancies in the past literature on the dissociations of taxonomic and thematic relations. To address this question, we examined the representational structure underlying the semantic space in different task contexts by applying representational similarity analysis (RSA) to EEG datasets. In a series of experiments, EEG signals were collected while participants named pictures under different task demands: 1) task demands directing attention to taxonomic categories of objects; 2) no task to draw attention to the taxonomic or thematic structure of objects; 3) task demands drawing attention to either taxonomic or thematic categories of the same set of objects. The RSA approach allows us to examine the pairwise similarity in scalp recorded amplitude patterns at each time point following the onset of the picture and relate it to theoretical taxonomic and thematic measures derived from computational models of semantics. Across all task contexts, the similarity structure of scalp recorded neural activity correlated better with taxonomic than thematic measures, in the time window of semantic processing previously identified by meta-analysis (Indefrey, 2011). Most strikingly, we found that the scalp-recorded patterns of neural activity between taxonomically-related items were more similar to each than the scalp-recorded patterns of neural activity for thematically-related or unrelated items, even in tasks that focused attention on thematic relationships. These results suggest that the principle semantic organization of these concepts during picture naming is taxonomic, and that, at least in the context of picture naming, the engagement of different semantic systems is not as flexible as has been argued by leading theories of semantic cognition. Indefrey, P. (2011). The spatial and temporal signatures of word production components: a critical update. Frontiers in psychology, 2, 255. Lambon Ralph, M. A., Jefferies, E., Patterson, K., & Rogers, T. T. (2017). The neural and computational bases of semantic cognition. Nature Reviews Neuroscience, 18, 42–55. Mirman, D., Landrigan, J. F., & Britt, A. E. (2017). Taxonomic and thematic semantic systems. Psychological Bulletin, 143(5), 499.

Topic Areas: Meaning: Lexical Semantics, Language Production