Neural Sensitivity to Word Frequency Modulated by Morphological Structure: Univariate and Multivariate Functional Magnetic Resonance Imaging Evidence from Korean

초록

A central question in psycholinguistics in visual word recog-nition is whether morphologically complex words are obligatorily decomposed into stems and affixes during visual word recogni-tion or whether whole-word access can occur when forms are frequent and familiar. The present study investigated how mor-phological complexity and lexical frequency jointly shape neural responses by leveraging Korean nominal inflection, whose trans-parent stem-suffix structure permits a clean dissociation between base (stem) frequency and surface (whole-word) fre-quency. Twenty-five native Korean speakers completed a rapid event-related fMRI lexical decision task involving simple and inflected nouns that varied parametrically in both frequency mea-sures. Representational similarity analysis revealed robust encoding of surface frequency-but not base frequency-in the inferior frontal gyrus pars opercularis and supramarginal gyrus, with significantly stronger correlations for inflected than simple nouns. Univariate analyses converged with this result: Sur-face frequency selectively increased activation for inflected nouns in inferior parietal regions, whereas base frequency showed no reliable effects in any ROI. These findings challenge models pos-iting obligatory prelexical decomposition and instead support accounts in which morphological processing is shaped by post-lexical, usage-driven lexical statistics. Taken together, our find-ings shed light on a distributed perspective on morphological processing, suggesting that structural and statistical factors jointly constrain access to morphologically complex forms.

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