Received 14 December 2004; received in revised form 21 February 2005; accepted 23 February 2005.
Abstract
Objective
The aim of this study was to determine whether low cognitive test scores in schizophrenia patients are due to insufficient effort and, if so, to what extent.
Method
Mental effort was measured with the Word Memory Test (WMT), an effort test that has been extensively validated. Schizophrenic patients (n=64), non-psychotic psychiatric patients (n=63), neurological controls (n=20), and normal controls (n=44) were tested with a neuropsychological test battery measuring memory, attention and executive functioning.
Results
The majority of the schizophrenia patients and a quarter of the psychiatric patients scored below the cut-offs for normal effort on the WMT. Scores on the effort test explained a significant amount of variance in the neuropsychological test performance of schizophrenic patients. This lends support to the notion that cognitive functioning in schizophrenia is compromised by insufficient effort. Furthermore, poor mental effort was related to negative symptoms.
Conclusions
Poor mental effort might be considered a core symptom of schizophrenia, representing an executive, monitoring or motivational problem. Mental effort should be taken into consideration in the neuropsychological assessment of schizophrenic patients and of psychiatric patients in general. Controlling for this variable may have a considerable impact on research, assessment and treatment of cognitive disorders in schizophrenic patients.
aPsychiatric hospital Meerkanten, Veldwijk Research Institute, PO box 1000, 3850 BA Ermelo, The Netherlands
bDepartment of Psychology, Psychiatric hospital of Mérida, Carretera de Valverde Km 2, 06800-Mérida (Badajoz), Spain
cAcademic Medical Center, Department of Neurology PO Box 22660, 1100 DD Amsterdam and Department of Psychonomics, University of Amsterdam, The Netherlands
Corresponding author. Present address: CNRS UMR 7593, Pavillon Clérambault, La Salpétrière, 47 Bd de l'Hôpital, 75013 Paris, France. Tel.: +33 1 42 16 17 44; fax: +33 1 53 79 07 70.
ABSTRACT