Concreteness effects on single Chinese character naming using mixed effects modeling of EEG data

Compared with abstract words, concrete words are responded to more quickly and accurately in various lexical processing tasks. They have also been found to elicit a more negative-going wave in the N400 time window with stronger effects in the frontal region, often followed by a sustained frontal negativity up to 1000ms post-stimulus onset. The effect in N400 is taken to reflect activities of a stronger and denser semantic network of concrete words, followed by their activation of visual imagery. The current study examined the ERP correlates of concreteness effects on semantic processing of single Chinese characters of different form classes (POS), including nouns, verbs and adjectives. A non-factorial paradigm was adopted in which 434 characters varying in ratings of concreteness, number of strokes, and frequency were presented. Twenty-two native Mandarin speakers participated in a semantic categorization task. Linear mixed-effects modeling (LMEM) was applied to estimate statistical effects of fixed factors and random factors of subject and item. Significant effects of POS, concreteness, and interactions were only found in the posterior regions (left, midline, and right) during the N400 and the right-posterior region during 500-1000ms. Greater N400 was associated with more concrete than less concrete nouns, whereas less negative N400 was found for concrete verbs relative to abstract verbs, resulting in an interaction between POS and concreteness. Concreteness continued to modulate neural response to verbs in the same pattern as in the N400 after 500ms. The effect and its interaction with POS were restricted to the right posterior region. The opposite directions of the effect on nouns and verbs can be explained by task demand, where abstract verbs generated greater conflicts with concrete semantic categories denoted by nouns. The late concreteness effect in the right hemisphere is taken to indicate activities of imagery processes linked to concrete items.