Proceedings of the Annual Meeting of the Cognitive Science Society

Sentence comprehension in part involves introducing, stor-ing, and retrieving information about individuals. Natural lan-guages provide various means for performing this computa-tional work. One popular idea is that indefinite noun phrasesprovide instructions for updating the discourse model byadding a new discourse referent, while definite noun phrasespresuppose the existence of a discourse referent available inmemory, as well as instructions for retrieving it. When no an-tecedent is available, the definite’s presupposition fails to besatisfied, resulting in the so-called ‘presupposition failure’ andpragmatic infelicity. However, under certain conditions, def-inite noun phrases can felicitously be used even when no an-tecedent is available in memory. In such cases, a conversa-tional repair strategy called ‘presupposition accommodation’can rescue the discourse by adding the required referent. Itis natural to expect greater processing costs for adding a dis-course referent with a definite than with an indefinite: althoughboth involve the process of adding a referent, definites gothrough a stage of presupposition failure and a subsequent de-cision to accommodate. The experimental challenge has beento apply a method sensitive enough to detect expected costsin discourse, even when the participant is unaware of the pre-supposition failure and repairs it rapidly. The present studyaddresses this challenge by using EEG to capture temporallyfine-grained processing differences between definite and indef-inite noun phrases when both introduce new discourse refer-ents in plausible and implausible contexts. Our main findingis that definite noun phrases elicit the Left Anterior Negativ-ity (LAN) effect, compared to indefinite noun phrases, bothin implausible contexts where there is a sense of oddness andin perfectly coherent contexts. We take this as evidence of aspecific cognitive stage at which presupposition failure is de-tected and when an accommodation decision occurs. This alsosupports the idea that, when encountering a definite, the LANis tightly linked to working memory processes involving thesearch for discourse elements that are presupposed to exist inmemory. When none are found, definites are subsequently ac-commodated and bridged to other entities in the discourse.