ERP correlates of orthographic typicality and lexicality in written

Running title: ERP effects of typicality and lexicality Abstract Using a speeded lexical decision task, event-related potentials (ERP) and minimum norm current source estimates, we investigated early spatio-temporal aspects of cortical activation elicited by words and pseudowords that varied in their orthographic typicality, i.e. in the frequency of their component letter pairs (bigrams) and triplets (trigrams). At around 100ms after stimulus onset, the ERP pattern revealed a significant typicality effect, where words and pseudowords with atypical orthography (e.g., yacht, cacht) elicited stronger brain activation than items characterised by typical spelling patterns (cart, yart). At ~ 200 ms, the ERP pattern revealed a significant lexicality effect, with pseudowords eliciting stronger brain activity than words. The two main factors interacted significantly at around 160 ms, where words showed a typicality effect but pseudowords did not. The principal cortical sources of the effects of both typicality and lexicality were localised in inferior temporal cortex. Around 160ms, atypical words elicited the stronger source currents in left anterior inferior temporal cortex, whereas left perisylvian cortex was the site of greater activation to typical words. Our data support distinct but interactive processing stages in word recognition, with surface features of the stimulus being processed before the word as a meaningful lexical entry. The interaction of typicality and lexicality can be explained by integration of information from the early form-based system and lexico-semantic processes.