A Direct Comparison of N400 Effects of Predictability and Incongruity in Adjective-Noun Combination

Introduction One of the core components of language comprehension is accessing the stored meanings of the individual words in a sentence or discourse and combining them to construct a global interpretation of the speaker’s message. Many critical questions about this process— questions about speed, automaticity, interactivity, and neural implementation— have been explored in the last 30 years through work with the ERP component known as the N400, which is modulated by a vast array of lexical and contextual factors thought to influence the processing of meaning (see [1], for review). This work has been so important and influential that the N400 response is familiar not only to specialists in the electrophysiology of language, but to many in the fields of cognitive psychology and cognitive neuroscience at large, appearing in broader reviews and textbook chapters. In this larger realm, the N400 is most often characterized as a response to ‘semantic anomaly’ [2], ‘semantic violation’ [3], ‘semantic incongruity’ [4] or ‘semantic mismatch’ [5] when the current word doesn’t ‘make sense’ in the context. In keeping with this, the example most often cited in textbooks comes from Kutas and Hillyard’s seminal 1980 work first reporting contextual modulation of the N400 [6], in which they compared the response to congruous and incongruous sentence endings such as It was his first day at work and He spread the warm bread with socks. However, much subsequent work has showed that a different but strongly correlated factor has an independent impact on N400 amplitude: lexical or conceptual predictability [7]. At a broad level, three possible accounts have been pursued: N400 effects of predictability and congruity might both be generated by a ‘combinatorial’ process like semantic integration [8, 9, 10], N400 effects of predictability and congruity might both be generated by an ‘access’ process like lexical/conceptual network activation [11, 12], or N400 effects of predictability might be generated by an access process and N400 effects of congruity might be generated by a combinatorial process (a ‘multiple generator’ account; [13, 14]). Discriminating between these accounts is of critical importance because the mechanism assumed to be driving N400 effects governs the conclusions about cognitive and neurocognitive models that are drawn on the basis of N400 results. In the current work we report three ERP experiments that argue against the first idea, that N400 effects of predictability directly reflect a combinatorial process such as integration difficulty, and are rather consistent with the ORIGINAL RESEARCH REPORT