The roles of object and action, and concreteness and imageability, in the distinction between nouns and verbs: An ERP study on monosyllabic words in Chinese

The dissociation between nouns and verbs has been reported in behavioral, electrophysiological, and neuroimaging studies. It is still unclear whether the spatial and temporal differences between nouns and verbs arise from semantic differences or morpho-syntactic differences associated with the two word classes. Regarding the semantic accounts, it is also unknown whether the word class effect should be attributed to differences in object and action, or in concreteness and imageability, associated with nouns and verbs. As the question with respect to semantic accounts for the word class effect is unsettled, the two types of semantic attributes have not been well distinguished in previous studies that support morpho-syntactic accounts, and this may lead to a confounding effect between morpho-syntactic factors and semantic factors. Therefore, to better understand the origins of the noun-verb distinction, it is essential to figure out whether the word class effect is driven by the contrast between object and action or by concreteness and imageability. With tight matching of stimuli and the use of event-related potentials (ERPs), we investigated the neural processing of monosyllabic nouns and verbs in Chinese that were presented without context. The results showed that when concreteness and imageability were balanced, nouns elicited more negative N400 than verbs over a broad scalp region, suggesting distinct semantic processing between the two word classes. Furthermore, nouns elicited more late negativity than verbs at frontal sites, which may reflect differences in the semantic representation of nouns and verbs in the working memory or differences in the working memory load associated with the word classes. These ERP results showed that the distinction between nouns and verbs persists even after concreteness and imageability are matched, revealing that the semantic account for the word class effect might arise from the contrast of object and action rather than the concreteness and imageability effect. The findings of the current study draw attention to the importance of object and action distinction in studies on nouns and verbs.