Normal cognitive conflict resolution in psychosis patients with and without schizophrenia

Schizophrenia is thought to be associated with impairments of executive functions, among which conflict control functions play an important role. The available evidence, however, suggests that conflict control is intact in schizophrenia, despite being based on methods that have successfully unveiled conflict control problems in other disorders. Differences between schizophrenia patients and healthy controls in stimulus perception, selective attention, alertness, processing speed and reaction time variability may have been previously overlooked. By controlling for these potential confounders, the present experiments were aimed to be more rigorous tests of the hypothesis that psychosis and schizophrenia are associated with impairments of conflict control. To that end, 27 healthy controls and 53 recent-onset psychosis patients with (n = 27) and without schizophrenia (n = 26) with comparable age, intelligence, and education level, performed three iconic conflict control tasks: the Simon task, the Eriksen flanker task, and the Stroop task, all equipped with neutral trials, and analyzed for various potential confounders. They further performed a battery of standard neuropsychological tests. Schizophrenia patients showed no increased conflict effects in any of the 3 tasks for any alternative measures used. Nonschizophrenia patients only showed abnormally increased response competition in the Simon task. All patients nevertheless demonstrated impaired control of attention and verbal memory. These findings indicate that the type of conflict control engaged by conflict tasks is intact in recent-onset schizophrenia, suggesting that a major component of executive function is spared in schizophrenia. We discuss these findings in terms of proactive and reactive control.