Windows into the positional encoding of stems and affixes: evidence from morpheme transposition effects via ERPs

While behavioural evidence has demonstrated that stems can be recognised irrespective of position and affixes are subject to more nuanced positional constraints, the present study employed EEG to observe this aspect of visual word recognition. Morphemically transposed compound nonwords (dreamday) elicited significantly reduced N250 and N400 ERP components relative to their controls (shadeday), as well as enhanced P600 activity. Conversely, transposed suffixed (fulplay) and prefixed (portex) nonwords did not elicit morpheme transposition effects relative to their controls (fulprofit, dockex), producing equivalent N250/N400/P600 components across conditions. Finally, robust morpheme transposition effects were found for semantically transparent conditions (fallwater vs. sellwater) across the N250, N400, and P600 components, whereas interference effects only emerged in the P600 time window for semantically opaque conditions (moonhoney vs. snowhoney). These findings offer insights into the morpho-orthographic and semantic processing that underlies morpheme transposition effects, further demonstrating the distinct positional encoding mechanisms of English stems and affixes.