Productivity matters for the neural processing of novel words, but not existing ones.

Every day, we are likely to encounter novel words. We might even make those ourselves from familiar parts of words we know, creating something new and understandable, e.g., wordify, grantology. However, some combinations of these familiar parts will yield words we are more likely to use: berater seems better than penciler or plantist. This depends on the productivity of the words' parts and how they combine: some suffixes, like -er in dreamer, are very often used to make a new word, reinforcing their use in more novel words. When encountering a novel word, how does the productivity of its stem-suffix combination affect its processing in the brain? How does its processing differ from the processing of words we know? Alongside productivity, do other properties like semantic ambiguity or the stem's syntactic category affect novel word processing? We investigated the neural dynamics of these properties using a lexical decision task in a MEG setting by contrasting existing and novel Verb-er ('tributer'), Noun-er (N-er 'legender'), and Noun-ist ('collagist') words. Throughout the temporal lobe, orbitofrontal cortex, and ventromedial prefrontal cortex, we found a distinction within novel words, with the most productive form (novel V-er) being processed significantly differently from the other novel word forms. Existing words, on the other hand, did not differ among each other, highlighting the elevated role of productivity in novel words. Importantly, existing-novel counterparts did not differ significantly in their processing. Innovatively investigating plausible novel words of different properties, our findings offer new insight on the role of morphological productivity in the comprehension of new words.