Event-related potentials to visual processing of incongruities in negated and affirmative sentences

In spite of the fact that negation has been the focus of many studies, the way it is processed in human communication still eludes us. Previous studies of negation using event-related potentials (ERPs) have reported inconclusive results as to whether or not negation poses difficulties for processing. While some have found that negation is initially ignored and incongruities in negated sentences do not modulate the N400 effect (Fischler et al., 1983; Lüdtke et al., 2008), others have reported that the N400 is modulated in incongruent negated sentences similarly to affirmative sentences (Nieuwland & Kuperberg, 2008). This research, however, has been limited to negators, such as “not” and “no” while prefixally negated forms with “un” are largely unexplored despite their frequency of use (Tottie, 1980). To make up for this, we pose two questions: 1) Is there a difficulty in the processing of negation as measured by ERPs? and 2) Are prefixally negated forms processed similarly to sententially negated forms or to affirmative forms? In order to answer these questions, the processing of affirmative (e.g., authorized), prefixally negated (e.g., unauthorized) and sententially negated (e.g., not authorized) adjectives was investigated in sentences such as "The details in the new Obama biography were correct/ wrong because the book was authorized/unauthorized/ not authorized by the White House". A member of an opposite pair (correct/wrong) in the first part of the sentence was combined with a negated or affirmative adjective (critical word) in the second part creating a semantically congruent or incongruent context. The amplitudes of the N400 (300-500 ms) and the P600 (500- 700 ms) to the critical words, as well as accuracy rates and response times to sentences were recorded and analyzed using mixed-effects modelling. The analyses of accuracy and response times suggested that sentential negation was more difficult to process than prefixal negation and affirmative forms. The ERP analyses were consistent with these results in that the most effortless processing was observed for affirmatives where incongruities elicited a larger N400, indicating a successful detection of the incongruities. Prefixal negation was more difficult than affirmative forms, resulting in an N400 combined with a P600 that indicated a re-evaluation of the sentence. Sentential negation seemed to be the most difficult form to process as the ERP effects of congruency were restricted to a P600, suggesting that incongruities in these sentences were processed differently compared to the other two conditions. In line with previous research, we conclude that sentential negation is more difficult to process than affirmatives and prefixal negation. We present two novel findings: 1) Different mechanisms are involved in processing incongruities in negated sentences (P600) than in affirmative sentences (N400), 2) Participants are as fast and accurate to judge prefixally negated sentences as they do affirmative sentences, but the neurocognitive processing patterns for prefixally negated forms are different suggesting a more demanding processing for these forms than affirmative forms