[Vulnerability to schizophrenia. III: Importance and limits of the Identical Pairs Continuous Performance Test]

Since several investigations have shown attentional deficits both in patients with schizophrenia and in subjects at high risk for schizophrenia, these deficits could be valuable vulnerability markers for schizophrenia. The aim of this study was to investigate wether non psychotic relatives of schizophrenic probands have deficits in sustained attention as measured by the Continuous Performance Test, Identical Pairs (CPT-IP) version. The study subjects were 25 schizophrenic probands, 50 of their first-degree relatives and 46 normal controls. For each subject, attention was assessed during 6 experimental conditions (2 standard, 2 slow, 2 easy conditions) of visual stimuli (digit-numbers and shapes). In each of the six conditions, the value of the sensitive index d' in the first-degree relative group was at an intermediate level between the patient and control groups. Moreover, in the standard shape condition, the d' value was significantly lower in the schizophrenic and in the relative groups than in the control group. This deficit was all the more interesting since it was not explained by a deficit in general intellectual abilities or by psychopathology such as anxiety or depression. Furthermore, the schizophrenic patients made more random errors in the standard and in the slow number conditions than both other groups. All groups improved their performance when the stimulus duration increased and when the processing load decreased. As a conclusion, this investigation seems: 1) to confirm the existence of an attentional deficit in the first-degree relatives of patients with schizophrenia; 2) to demonstrate the interest of the CPT-IP to detect this deficit. It must be emphasized that in order to detect the deficit, one only needs to explore the standard shape condition and that under such circumstances, the CPT-IP test has the advantage of being less time consuming than tests used in previous studies.