Abstract
The ability to represent concepts and the relationships between them is critical to human cognition. How does the brain code relationships between items that share basic conceptual properties (e.g., dog and wolf) while simultaneously representing associative links between dissimilar items that co-occur in particular contexts (e.g., dog and bone)? To clarify the neural bases of these semantic components in neurologically intact participants, both types of semantic relationship were investigated in an fMRI study optimized for anterior temporal lobe (ATL) coverage. The clear principal finding was that the same core semantic network (ATL, superior temporal sulcus, ventral prefrontal cortex) was equivalently engaged when participants made semantic judgments on the basis of association or conceptual similarity. Direct comparisons revealed small, weaker differences for conceptual similarity > associative decisions (e.g., inferior prefrontal cortex) and associative > conceptual similarity (e.g., ventral parietal cortex) which appear to reflect graded differences in task difficulty. Indeed, once reaction time was entered as a covariate into the analysis, no associative versus category differences remained. The paper concludes with a discussion of how categorical/feature-based and associative relationships might be represented within a single, unified semantic system.
Highlights
Investigating the nature of semantic representation has been a core pursuit in many different disciplines, including philosophy, linguistics, cognitive science, and neuroscience
The central question addressed in this study was: do semantic association and conceptual similarity arise from neuroanatomically separable components of semantic memory or are they the result of a single conceptualization process? In particular, we contrasted the alternative predictions made by the “dual-hub” theories of conceptualization versus the single “hub-and-spoke” framework
This shows the high signal found with dual-echo echo planar imaging (EPI) throughout the brain including in key inferior temporal and frontal regions
Summary
Investigating the nature of semantic representation has been a core pursuit in many different disciplines, including philosophy, linguistics, cognitive science, and neuroscience. We can correctly ascribe similar properties and actions to croissants, scones, crumpets, and naan bread, despite them having very different physical forms and occurring in different contexts. Both kinds of relationship types are central to the normal semantic cognition of adults (Lin and Murphy 2001). Many researchers have proposed different hypotheses on how these coherent, generalizable concepts are formed and, this key dimension of semantic memory is given various theory-specific labels: family resemblances (Wittgenstein 1953); taxonomical/categorical similarity (Quillian 1968); prototypicality (Rosch 1975); feature-similarity For the sake of brevity, the theory-neutral term conceptual similarity will be used forth
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