A meaningful item, such as a word, object or face, that is unexpected in a given context, elicits the N400, an event-related potential (ERP) thought to index the amount of effort applied to integrate the item in its context. This N400 has repeatedly been found to be abnormal in schizophrenia (Sz) patients. Meanwhile, these patients are also deficient at maintaining context in mind, which, like the inability to integrate an item, can cause a comprehension deficit. The maintenance of context can be assessed by measuring another component of ERPs, the contingent negative variation (CNV). The CNV is evoked by a context stimulus that is presented just before a target stimulus. As yet, the N400 and the CNV have not been studied together in order to assess the respective roles of contextual integration and context maintenance in semantic performance. To this end, Sz subjects and normal controls were asked to perform semantic categorizations for word, face, and object targets in an experiment in which each categorization was specified by a context instruction stimulus presented just before each target stimulus. / The extent to which context maintenance and contextual integration impairments could be related to the thought-disorders (TD) of Sz patients was assessed. Therefore, high (n=15) and low (n=15) TD patients were compared to high (n=15) and low (n=15) TD normal controls. It is proposed that the excess of information extracted from instructions and targets, as indicated by larger than normal P600s to both types of stimuli in high TD patients, may actually be the root cause underlying thought disorder.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.81349 |
| Date | January 2004 |
| Creators | Kumar, Namita |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science (Division of Neuroscience.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 002166351, proquestno: AAIMR06412, Theses scanned by UMI/ProQuest. |
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