Dispreferred adjective orders elicit brain responses associated with lexico-semantic rather than syntactic processing.

We examined how adjective ordering is used in language comprehension by crossing order preference and concreteness in phrases consisting of two adjectives and a noun. We used both more typical phrases in which the preferred order has a concrete second adjective ("exhaustive hardback encyclopedia") and those with a concrete first adjective in the preferred order ("heavy informative encyclopedia"). We found that concreteness-related modulations of the ERP waveform were likely responsible for prior reports of increased positivity to dispreferred orders (interpreted as a syntactic P600-like effect). When concreteness is controlled, instead, we found that dispreferred orders are associated with larger N400s to the second adjective and following noun. This suggests that dispreferred adjective orders impact lexico-semantic predictability and the ability to generate mental images of the referent but do not result in syntactic processing difficulties.