Who jumps to conclusions? A comprehensive assessment of probabilistic reasoning in psychosis following traumatic brain injury (PFTBI)

Background: To jump to a conclusion is the act of making a decision based on insufficient or poor evidence. Probabilistic reasoning impairment, which may underpin a jumping to conclusions (JTC) bias, has received robust discussion in the schizophrenia and delusion literature as an important component of poor cognition in psychosis. However, reasoning biases have not been explored in PFTBI to date. Methods: Probabilistic reasoning was investigated in dually diagnosed PFTBI patients using an adaptation of Huq et al.'s (1988) original beads task design with the ratios 85:15 and 60:40. Probabilistic predictions, draws-to-decision, self-rated decision confidence, and JTC bias were recorded. These data were compared to responses from patients with traumatic brain injury, schizophrenia, and healthy controls. Results: PFTBI patients demonstrated the poorest predictions but the highest self-rated confidence of any of the cohorts. Furthermore, patients from both psychotic cohorts took the longest draws-to-decision in the first, and easier, trial (85:15), but responded the fastest in the second, and more difficult, trial (60:40). JTC behaviour was not evident in PFTBI over and above the other cohorts. Conclusions: PFTBI appears to be associated with some initial caution in decision making requiring probabilistic reasoning, but this may give way to an overconfident and more rushed decision making process once patients become familiar with a task. This process, however, may not constitute a JTC cognitive bias