Language, Cognition and Neuroscience.
Morpheme transpositions were examined across three experiments using EEG and lexical decision tasks to investigate the positional encoding mechanisms of English stems and affixes. Across three experiments, morphemically transposed compound nonwords (dreamday) elicited significantly reduced N250 and N400 components relative to their controls (shadeday), as well as greater interference in the behavioural data and an enhanced P600. Conversely, transposed suffixed (fulplay) and prefixed nonwords (qualifydis) did not elicit morpheme transposition effects relative to controls, as evidenced by equivalent N250/N400/P600 components across conditions. Finally, the direct comparison between transparent and opaque compound words revealed robust transposition effects in the transparent conditions (fallwater vs. sellwater) across the N250, N400, and P600 components, whereas in the opaque condition (moonhoney vs. snowhoney), this effect was only found in the P600. Our findings point to the automaticity of compound word processing and highlight key differences in the positional encoding of stems and affixes in reading.