Introduction: Previous studies confirmed a bias against disconfirmatory evidence (BADE) for both delusional and delusion-neutral events in paranoid schizophrenia. In the present study, we examined a potential relationship between the BADE and delusional ideation.
Methods: Fifty-five patients with schizophrenia (32 with current delusions), 20 patients with obsessive-compulsive disorder and 30 healthy participants were presented written scenarios composed of three successive sentences which increasingly disambiguated the situation. Participants were asked to rate interpretations presented along with the sentences. After each new sentence, participants could adjust their judgements in view of the new information. One interpretation ("true") did not seem to fit the first statement but became increasingly plausible, whereas "lure" interpretations appeared very likely initially but were eventually incorrect. Patients were given the option to decide for one of the statements.
Results: Patients with schizophrenia, irrespective of delusion severity, attenuated their ratings significantly less for lure interpretations in face of disconfirmatory evidence (BADE) compared to both control groups. We found no impairment regarding the integration of confirmatory evidence. Patients with schizophrenia made more incorrect decisions after the first sentence indicating jumping to conclusions relative to healthy controls. Participants with schizophrenia showed a lowered decision threshold compared to the controls.
Conclusions: The findings lend further evidence to the claim that patients with schizophrenia are hastier and rather inflexible in their decision making. This response pattern may represent a trait-like vulnerability factor for the emergence of delusional incorrigibility, a hallmark symptom of schizophrenia.