As easy as cake or a piece of pie? Processing idiom variation and the contribution of individual cognitive differences

Language users routinely use canonical, familiar idioms in everyday communication without difficulty. However, creativity in idiom use is more widespread than sometimes assumed, and little is known about how we process creative uses of idioms, and how individual differences in cognitive skills contribute to this. We used eye-tracking while reading and cross-modal priming to investigate the processing of idioms (e.g. play with fire) compared to creative variants (play with acid) and literal controls (play with toys), amongst a group of 47 university level native speakers of English. We also conducted a series of tests to measure cognitive abilities (working memory capacity, inhibitory control and processing speed). Eye-tracking results showed that in early reading behaviour, variants were read no differently to literal phrases or idioms, but showed significantly longer overall reading times, with more re-reading required compared to other conditions. Idiom variables (familiarity, decomposability, literal plausibility) and individual cognitive variables had limited effects throughout, although more decomposable phrases of all kinds required less overall reading time. Cross-modal priming – which has often shown a robust idiom advantage in past studies – demonstrated no difference between conditions, but decomposability again led to faster processing. Overall, results suggest that variants were treated more like literal phrases than novel metaphors, with subsequent effort required to make sense of these in the way that was consistent with the context provided.