Background. We investigated whether schizophrenic subjects
are impaired in non-routine behaviour
because of the dysfunction of a general executive component labelled,
in neuropsychological terms, the supervisory system.
Methods. A specific verbal sequencing test was designed for
Subjects had to perform
sequential reasoning with verbal material. Each test sequence consisted
series of words
presented in jumbled order. The construction of some sequences had to be
done using familiar
routine associations (valid conditions). In contrast, some other sequences
required the overriding
selection of familiar routine associations, which were inappropriate within
the general context of the
task (invalid conditions). Twenty verbal sequences (10 valid–10 invalid)
were administered. Thirty-seven DMS-IV schizophrenic patients and 21 normal
volunteers matched for age and educational level were recruited.
Results. Compared to the control group the schizophrenic group
impaired in both valid and
invalid conditions. The number of ‘capture errors’ specific
supervisory system failure was
significantly higher in the schizophrenic group and only the schizophrenic
patients had significantly
fewer correct sequences in invalid conditions than in valid conditions.
performance in invalid conditions alone was observed only among the schizophrenic
subjects without a general cognitive defect.
Conclusions. These findings suggest that sequencing procedures
an executive input are impaired in schizophrenia.