Post-conclusion belief inflexibility bias assessed by a modified beads task in schizophrenia

A key defining feature of delusions in psychiatric practice is their incorrigibility, reflecting marked cognitive inflexibility. Among cognitive biases in schizophrenia, belief inflexibility explains the maintenance of delusions, whereas the jumping-to-conclusions bias relates to delusion formation. However, belief inflexibility once a conclusion has been reached, which may more directly reflect the maintenance process following formation, has not yet been investigated.

Twenty-nine patients with schizophrenia (SZ) and twenty-eight healthy controls (HC) completed a modified beads task that separated phases reflecting cognitive processes involved in delusion formation (Phase 1) and maintenance (Phase 2). In Phase 1, following the classical beads task paradigm, beads were drawn one by one from one of two jars. After each draw, participants were asked whether they could state a conclusion about which jar was being used. Phase 1 ended once a conclusion was reached with sufficient confidence. In Phase 2, bead drawing continued, and participants judged whether to withdraw their Phase 1 conclusion. In some trials, subsequent bead colours contradicted the conclusion, favouring withdrawal.

In Phase 1, the number of beads required to reach a conclusion did not differ significantly between groups. In Phase 2, however, SZ required significantly more beads to withdraw their prior conclusion, with this delayed withdrawal being particularly evident in those with delusion-predominant symptoms.

These findings are consistent with the notion that post-conclusion belief inflexibility contributes to the maintenance of delusions, providing empirical support for models of delusion maintenance distinct from those addressing delusion formation.