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Processing speed deficits in schizophrenia: reexamining the evidence.
Emma E M Knowles1, Anthony S David, Abraham Reichenberg
1Department of Psychosis Studies, Institute of Psychiatry, King's Health Partners, King's College London, De Crespigny Park, London, SE5 8AF UK. emma.knowles@kcl.ac.uk
The American Journal of Psychiatry
|May 5, 2010
Summary
Schizophrenia impairs cognitive processing speed, particularly in coding tasks. Antipsychotic medication dosage significantly impacts this impairment, highlighting its role as a key moderator.
Area of Science:
- Neuroscience
- Psychiatry
- Cognitive Psychology
Background:
- Schizophrenia is characterized by significant cognitive deficits, with processing speed inefficiency being a primary impairment.
- Previous meta-analyses identified processing speed deficits but did not fully clarify the influence of moderator variables like medication and illness severity.
Purpose of the Study:
- To conduct an extended meta-analysis of cognitive functions in schizophrenia, focusing on processing speed.
- To investigate the impact of moderator variables, including antipsychotic medication dosage, on cognitive performance in schizophrenia.
Main Methods:
- Systematic literature searches of MEDLINE and PsycINFO were performed to identify relevant studies published between May 2006 and January 2009.
- Data on moderator variables (publication year, illness severity, chlorpromazine equivalent daily dose, IQ, age, sample size) were extracted.
- Meta-analysis, meta-influence, and homogeneity analyses were conducted to calculate effect sizes and assess moderator effects.
Main Results:
- The extended meta-analysis included 4,135 participants with schizophrenia.
- Coding tasks exhibited the largest effect size (g=-1.50), indicating severe processing speed impairment.
- Metaregression revealed that publication year, IQ difference, and chlorpromazine equivalent daily dose significantly moderated the effect size for coding tasks, with medication dosage showing a notable impact.
Conclusions:
- Processing speed deficits in schizophrenia are significantly influenced by moderating factors.
- Antipsychotic medication dosage is a critical moderator of processing speed impairment in individuals with schizophrenia.
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