The costs of freedom: an ERP -- study of non-canonical sentences.

Objectives: The present investigation explored the electrophysiological correlates of working memory during sentence comprehension.

Methods: Event-related brain potentials (ERP) were recorded from 29 channels in 22 subjects, while they read German sentences having subject-first (canonical) or object-first (non-canonical) word orders.

Results: Three different ERP effects were observed: a negativity (maximum at Fc5) differentiating unambiguous object-first and subject-first sentences, interpreted as reflecting the demands of the object-first sentences on working memory; a second negativity (maximum at F7) to the subject noun-phrase in object-first sentences, interpreted as indicating retrieval of verbal material. Finally, a parietal positivity was found for ambiguous sentences that turned out to have a non-canonical word order, which was interpreted as indicating revision and reevaluation processes.

Conclusions: The present data underscore the different roles of working memory in comprehension.