Introduction: People with delusional beliefs "jump to conclusions" (JTC). This finding is well replicated. However, there is only limited exploration of the factors that might lead a person to JTC. The aim of the present study was to explore the contribution of working memory processes (WM) and IQ to hasty decision making and to investigate the stability of this bias over time.
Methods: A single group cross-sectional design was utilised. The study was conducted in 2 phases: (1) an initial screening phase and (2) an experimental phase whereby we explored and tested hypotheses regarding the cognitive origins of the JTC bias. In Study 1, participants completed the beads task as well as measures of mood and symptoms. In Study 2, the same participants repeated the beads task, and completed a battery of neuropsychological tests designed to assess different facets of WM and IQ.
Results: In most cases, "jumpers" were indistinguishable from "nonjumpers" in terms of their neuropsychological profiles. The only exception to this pattern was for visual working memory, in which "jumpers" performed better than "nonjumpers". In terms of the temporal stability of the JTC bias, 8 individuals (out of the 29) effectively switched from being "jumpers" at T1 to "nonjumpers" at T2.
Conclusions: This study casts doubt on reduced global WM as an explanation of JTC. Rather it may be that the differences in reasoning are related to the manipulation of visual material and do not extend to other areas of neuropsychological functioning. However, as our sample is small it may be underpowered to detect important differences. Future work is therefore needed to replicate these findings.