Representational similarity analysis reveals task-dependent semantic influence of the visual word form area

Xiaosha Wang,Yanchao Bi,Jiacai Zhang,Yuwei Wang,Yangwen Xu,Yi Zeng,Zhenhua Ling

doi:10.1038/s41598-018-21062-0

Abstract

Access to semantic information of visual word forms is a key component of reading comprehension. In this study, we examined the involvement of the visual word form area (VWFA) in this process by investigating whether and how the activity patterns of the VWFA are influenced by semantic information during semantic tasks. We asked participants to perform two semantic tasks - taxonomic or thematic categorization - on visual words while obtaining the blood-oxygen-level-dependent (BOLD) fMRI responses to each word. Representational similarity analysis with four types of semantic relations (taxonomic, thematic, subjective semantic rating and word2vec) revealed that neural activity patterns of the VWFA were associated with taxonomic information only in the taxonomic task, with thematic information only in the thematic task and with the composite semantic information measured by word2vec in both semantic tasks. Furthermore, the semantic information in the VWFA cannot be explained by confounding factors including orthographic, low-level visual and phonological information. These findings provide positive evidence for the presence of both orthographic and task-relevant semantic information in the VWFA and have significant implications for the neurobiological basis of reading.

Highlights

The left posterior occipitotemporal sulcus is a key region in the neural circuitry of reading
The aim of this study was to investigate whether the visual word form area (VWFA) activity encodes semantic information in explicit semantic tasks
Using representational similarity analysis (RSA), we computed the correlations between representational dissimilarity matrices (RDMs) derived from neural activity patterns in the VWFA with various types of semantic RDMs in two semantic categorization tasks–taxonomic and thematic categorization

Summary

Introduction

The left posterior occipitotemporal sulcus is a key region in the neural circuitry of reading It is consistently activated by visual words across various writing systems[1,2], adapts to repeated presentation of words[3,4,5] and captures orthographic similarity among words[6,7,8]. Its sensitivity to visual words develops with reading acquisition[9,10] and decreases upon damage[11,12] All these lines of evidence indicate the involvement of this region in orthographic representation and justify its name as the “visual word form area” (VWFA)[13]. We constructed semantic representational dissimilarity matrices (RDMs) based on four types of semantic relations: taxonomic, thematic, subjective semantic rating and word2vec[25] (a computational linguistic measure based on word co-occurrence patterns in a large language corpus) (Figure 1, top panel). Orthographic, low-level visual and phonological RDMs were constructed and controlled for in further analyses to rule out the possibility that any semantic effects may be driven by these non-semantic information types in this region

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Conclusion