The integration of semantic versus world knowledge during on-line sentence comprehension

Abstract

The current research was aimed at addressing several specific questions regarding the integration of world knowledge during language comprehension. First, what is the time course of the on-line integration of semantic and world knowledge information? Secondly, which are the crucial brain areas involved in these processes? It is a long-standing issue whether or not semantic information is prepackaged into the mental lexicon and therefore more immediately available than world knowledge that is necessary to assign a truth-value to a sentence. Two ERP studies were performed to investigate this question. Subjects were presented with sentences like the following types (critical words are underlined): (a) "Amsterdam is a city that is very old and lively." (Correct); (b) "Amsterdam is a city that is very new and lively." (World Knowledge Violation); (c) "Amsterdam is a city that is very thin and lively." (Semantic Violation). Sentence (b) is semantically well-formed, but not true, when considering the founding date of Amsterdam. In contrast, in sentence (c) the semantics of the noun "city" makes the adjective "thin" not applicable. The question was whether or not the waveforms for (b) would result in an N400 effect with the same latency and topography as a lexical semantic N400-effect (c). The ERP waveforms for both (b) and (c) resulted in a clear and sizable N400 effect, with comparable onset and peak latencies. Additionally, (c), but not (b) resulted in an additional late positivity with a posterior distribution. To address the second issue: what are the crucial brain areas involved in these processes, a fMRI version of the experiment was performed. Results indicated that both (b) and (c) activated the left inferior frontal gyrus. In addition, (c), but not (a) or (b), resulted in activation of the left posterior parietal region. Post-integration processes may be responsible for this differential activation found for the world knowledge and semantic conditions. The results of this research indicate that during on-line sentence comprehension world knowledge information is integrated as quickly as lexical semantic information. The left prefrontal cortex might be involved in this recruitment/integration process.