Semantic Processing Disturbance in Patients with Schizophrenia: A Meta-Analysis of the N400 Component.

Background: Theoretically semantic processing can be separated into early automatic semantic activation and late contextualization. Semantic processing deficits have been suggested in patients with schizophrenia, however it is not clear which stage of semantic processing is impaired. We attempted to clarify this issue by conducting a meta-analysis of the N400 component. Methods: Twenty-one studies met the inclusion criteria for the meta-analysis procedure. The Comprehensive Meta-Analysis software package was used to compute pooled effect sizes and homogeneity. Results: Studies favoring early automatic activation produced a significant effect size of 20.41 for the N400 effect. Studies favoring late contextualization generated a significant effect size of 20.36 for the N400 effect, a significant effect size of 20.52 for N400 for congruent/related target words, and a significant effect size of 0.82 for the N400 peak latency. Conclusion: These findings suggest the automatic spreading activation process in patients with schizophrenia is very similar for closely related concepts and weakly or remotely related concepts, while late contextualization may be associated with impairments in processing semantically congruent context accompanied by slow processing speed. [ABSTRACT FROM AUTHOR]