|M.Sc Student||Mordkovitz Nirit|
|Subject||A Comparison of Sentence and Discourse Level Semantic|
Processing: An ERP Study
|Department||Department of Medicine||Supervisor||Professor Emeritus Hillel Pratt|
Brain activity was studied while subjects processed words integrated in spoken sentences and discourse contexts. Some multi stage language models have argued that local semantics of a sentence is processed before relating the sentence to the wider semantics of the preceding context. Others have argued that there is no difference between semantic integration at the level of a sentence and a global semantic integration at discourse level. Eighteen subjects listened to sentences ending with semantically congruent or incongruent words. Each congruent sentence was embedded at the end of a short story so that the final word was semantically acceptable at the sentence level but incongruent in terms of discourse context. The same stories were also presented with congruent endings. Auditory ERPs elicited by final words in sentences and in discourse contexts were compared. Both sentence- and discourse level semantic integration were associated with N400 and Late Positive Component (LPC) effects in addition to a new and unexpected component, P550. Findings indicate similar cognitive processing underlying local- and global semantic processing. These processes, although evoking the same components, were characterized by differential effects on amplitudes according to the amount of text integrated and its clarity and congruence. These results indicate similar cognitive processes of contexts build up, underlying sentence- and discourse- semantic processing. Thus, comprehension appears to proceed as the ongoing integrated mental representation is being formed while the content is being heard, without distinguishing between the two levels of the unfolding context.