A brief, single session training intervention had an effect
on data gathering, reflected in a significant increase
immediately after training in the number of beads
requested on both versions of the beads task. The study
therefore demonstrates that it is possible to change the
data gathering of people with delusions, in the short
term. The change was greater on the 60:40 version of
the beads task. Why was there a difference in training
effects on the 2 tasks? It could be that the training was
only weakly effective, or it might be explained by the level
of difficulty of the 2 tasks. The 85:15 task is much easier than the 60:40 version and can be successfully solved after
a small number of draws. There is less objective benefit in
delaying a decision on the 85:15 task because it is clear at
a very early stage which jar has been chosen, and delaying
the decision is unlikely to increase accuracy. The 60:40
task is more difficult because the ratio of the beads in
the 2 jars is very similar, and delaying a decision is
more beneficial in reaching a correct solution. The central
theme of the training that gathering information is helpful
has more relevance to the more difficult version of the
beads task.
An interesting finding adds a note of caution to interpreting
the training effects. Although there was an overall
group mean increase of about 50% in the number of
beads requested on the beads task from pre- to posttraining,
the numbers of participants showing the extreme
JTC bias remained consistent. On average, all participants
in the intervention group improved, compared
with the controls, but the amount of improvement was
dependent on their baseline measurement. The effect
was much smaller in those with the extreme bias. As
noted in the introduction, a prior JTC bias has recently
been found to moderate change in response to antipsychotic
medication27; in this study, a prior JTC bias moderated
the effects of reasoning training. It was clear that
training improved data gathering more among those individuals
with delusions who did not show the JTC bias at
the outset. This leads to the conclusion that JTC in people
with delusions is a strong bias that is somewhat unresponsive
to only a brief training intervention.
We were also interested in the effects of reasoning
training on thinking about delusions and on delusional
conviction. This is of theoretical importance because if
a reasoning bias contributes to delusion formation and
maintenance, as hypothesized, reversing this bias should
have an impact on delusional thinking.16 It also provides
a test of a general effect of the training in addition to
training participants in gathering data. Our delusion
group at baseline had little belief flexibility and very
high levels of conviction in their beliefs. It should be
noted that the training content at no point considered delusion-
relevant material nor were the individual’s delusions
ever discussed. We were specifically interested in
examining whether a focus on general reasoning strategies
might generalize to affect thinking about delusions,
thereby providing some further evidence for a causal role
of reasoning in delusions. After training, 24% (n = 4)
showed greater belief flexibility and 18% (n = 3) some reduction
in delusional conviction. In contrast, only one
patient in the control group showed a change in belief
flexibility, and none changed at all in conviction. Although
only preliminary, this is an indication both of
a causal role and of the potential benefits for delusions
of reasoning training, suggesting that change in data
gathering and reasoning strategies might indeed mediate
change in delusional thinking. A larger study, powered