Who “jumps to conclusions”? A comprehensive assessment of probabilistic reasoning in psychosis following traumatic brain injury (PFTBI), and comparison with TBI, schizophrenia, and nonclinical controls

ABSTRACT

Introduction. The “jumping to conclusions” (JTC) bias has received significant attention in the schizophrenia and delusion literature as an important aspect of cognition characterising psychosis. The JTC bias has not been explored in psychosis following traumatic brain injury (PFTBI).

Methods. JTC was investigated in 10 patients with PFTBI using the beads task (ratios 85:15 and 60:40). Probabilistic predictions, draws-to-decision, self-rated decision confidence, and JTC bias were recorded. Responses from 10 patients with traumatic brain injury (TBI), 23 patients with schizophrenia, and 23 nonclinical controls were compared. Relationships were explored between draws-to-decision and current intelligence quotient, affective state, executive function, delusions (severity and type), and illness chronicity (duration).

Results. Groups were comparable on JTC measures. Delusion severity and type were not related to draws-to-decision for either trial. In the entire sample, executive function (reduced mental flexibility) was significantly related to more draws-to-decision on the 60:40 ratio trial.

Conclusions. We found no evidence for an elevated JTC bias in patients with PFTBI or TBI alone. The influence of executive dysfunction should be considered by future studies using the beads tasks in patient populations. These findings need to be replicated in larger PFTBI and TBI samples.

KEYWORDS:

• Psychosis
• schizophrenia
• traumatic brain injury
• jumping to conclusions
• reasoning bias

Acknowledgements

The authors thank Lisa Johnston from the Monash-Epworth Rehabilitation Research Centre, Richmond, for her assistance in recruiting patients with TBIWP.

Disclosure statement

No potential conflict of interest was reported by the authors.

Funding

This research was supported by the Austin Hospital Research Foundation under [Grant number 2-1372] and an Australian Postgraduate Award.

ORCID

Rachel A. Batty http://orcid.org/0000-0001-6413-5332

Notes

1. See Maher (1992, pp. 265–266) for discussion on the methodologically flawed nature of using ratios 85/15 alone.

2. The predetermined order of beads was taken from Colbert and Peters (2002) for the first trial (85:15 ratio), and from Dudley, John, Young, and Over (1997a) for the second trial (60:40). Two versions of randomisation were used per trial (the second was the inverse order of the first) and these were counterbalanced across participants.

3. PFTBI patients demonstrated significantly reduced performance on all executive function measures used in this study. See Batty et al. (2015a, 2015c) for these group-wise analyses.