Failure of hypothesis evaluation as a factor in delusional belief

ABSTRACT

Introduction

In accounts of the two-factor theory of delusional belief, the second factor in this theory has been referred to only in the most general terms, as a failure in the processes of hypothesis evaluation, with no attempt to characterise those processes in any detail. Coltheart and Davies ([2021]. How unexpected observations lead to new beliefs: A Peircean pathway. Consciousness and Cognition, 87, 103037. https://doi.org/10.1016/j.concog.2020.103037) attempted such a characterisation, proposing a detailed eight-step model of how unexpected observations lead to new beliefs based on the concept of abductive inference as introduced by Charles Sanders Peirce.

Methods

In this paper, we apply that model to the explanation of various forms of delusional belief.

Results

We provide evidence that in cases of delusion there is a specific failure of the seventh step in our model: the step at which predictions from (delusional) hypotheses are considered in the light of relevant evidence.

Conclusions

In the two-factor theory of delusional belief, the second factor consists of a failure to reject hypotheses in the face of disconfirmatory evidence.

KEYWORDS:

• Delusion
• two-factor theory
• abduction
• Charles Sanders Peirce
• bias against disconfirmatory evidence

Acknowledgements

We thank three anonymous reviewers for their insightful and constructive critiques of an earlier version of this paper.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1 https://maxcoltheart.wordpress.com/the-two-factor-theory-of-delusion/ lists all 27 papers from our group concerning this theory of delusion.

2 The text cites Coltheart (2007) and Coltheart et al. (2011) as the source of these arguments.

3 Maher (1974, 1999) argued that delusions arise as explanations of unusual perceptual phenomena and Maher and Ross (1984) set out a five-step model that shares some components with our eight-step “Peircean pathway” model. Maher and Ross’s first two steps, initial observation of an unexpected event and experience of puzzlement (which includes development of a preliminary hypothesis), correspond to the first two steps of our model; and their third step, additional observations, corresponds to the hypothesis evaluation stage (Steps 5–7) of our model. Maher and Ross’s fourth step, the explanatory insight, corresponds to the hypothesis generation stage (Steps 2–4) of our model, but only in cases where the generated hypothesis is assessed (at Step 3) as one which, if true, would provide a great deal of understanding of why the surprising fact was observed and, consequently, is considered (at Step 4) to be especially pursuit-worthy. Maher and Ross’s final step, the process of confirmation, might be understood as skipping the hypothesis evaluation stage and proceeding directly from the fourth Peircean step to the eighth. (Peirce, himself, acknowledged this possibility. For discussion, see Section 2.9 of Davies & Coltheart, 2020, and Coltheart & Davies, 2021, p. 3.)

4 Rosita Borlimi, personal communication, 15 July 2020.

5 In Figure 1, Step 6 of our “Peircean pathway” model follows Peirce, himself, who usually talked about experimental testing of predictions. But predictions can also be tested by observations (without there being any experimental manipulation involved) or just by using already-existing knowledge.

6 The “evidence integration” component is thus a kind of composite score for bias against disconfirmatory evidence and bias against confirmatory evidence.

7 The SPQ includes three subscales that directly assess, in nonclinical populations, tendencies towards having delusional beliefs: Ideas of Reference, Odd Beliefs or Magical Thinking, and Suspiciousness.

8 Davies et al. (2001) adopted a suggestion by Ramachandran and Blakeslee (1998, p. 171). We note that Langdon et al. (2014) argue, against this suggestion, that “the Fregoli delusional content is generated when hyperexcitation from the cognitive system to the PINs [person identity nodes] causes a known person to be identified as present, even when no matching face is also present” (p. 628).

9 Hypothesised by Ramachandran and Blakeslee (1998, p. 167).

Additional information

Notes on contributors

Max Coltheart

Max Coltheart is a cognitive neuropsychologist interested in understanding how delusional beliefs come about and also in acquired and developmental disorders of reading and spelling.

Martin Davies

Martin Davies is a philosopher and cognitive scientist interested in anosognosia and other delusions, implicit knowledge, and the methodology of cognitive neuropsychology.