2.1. Participants

Four groups of 20 patients with schizophrenia each and four groups of 30 healthy participants each volunteered to participate in the study. To each task (motor, superordinate, social motor, and social superord. tasks) were assigned one group of patients and one group of comparison participants among the aforementioned ones. Healthy participants were systematically matched with patients for sex, age, handedness (Oldfield, 1971)and years of education (see Table 1). None of them reported psychiatric problems.

Patients recruited fulfilled DSM-IV (American Psychiatric Association, 1994) criteria of schizophrenia, with no other psychiatric diagnosis on DSM-IV Axis I. All patients were receiving antipsychotic medication and were clinically stable at the time of testing (Table 1). Negative and positive symptoms were evaluated with the SANS (Andreasen, 1983) and the SAPS (Andreasen, 1984). A disorganization score was also computed by summing the following subscores: bizarre behavior, positive formal thought disorder, alogia, and inappropriate affect. Each group of patients was matched with the three others for the severity of negative, positive and disorganization symptoms (Table 1). In the social motor task, one patient performed at the chance-level and was therefore excluded from analyses (n=19).

For all groups, exclusion criteria included history of neurological illness or trauma, alcohol or drug dependence according to DSM-IV criteria, analphabetism, and age older than 60 years. All participants reported normal or corrected-to-normal visual acuity. After complete description of the study to the subjects, written informed consent was obtained. This research was approved by the local Ethical Committee (B80631-60). All participants received 10 euros for taking part in the study.