Continuing commentary: challenges or misunderstandings? A defence of the two-factor theory against the challenges to its logic

ABSTRACT

Corlett, P. R. (2019. Factor one, familiarity and frontal cortex: A challenge to the two-factor theory of delusions. Cognitive Neuropsychiatry, 24(3), 165–177. doi:10.1080/13546805.2019.1606706) raises two groups of challenges against the two-factor theory of delusions: One focuses on weighing “the evidence for … the two-factor theory”; the other aims to question “the logic of the two-factor theory” (ibid., p. 166). McKay, R. (2019. Measles, magic and misidentifications: A defence of the two-factor theory of delusions. Cognitive Neuropsychiatry, 24(3), 183–190. doi:10.1080/13546805.2019.1607273) has robustly defended the two-factor theory against the first group. But the second group, which Corlett believes is in many aspects independent of the first group and Darby, R. R. (2019. A network-based response to the two-factor theory of delusion formation. Cognitive Neuropsychiatry, 24(3), 178–182. doi:10.1080/13546805.2019.1606709, p. 180) takes as “[t]he most important challenge to the two-factor theory raised by Dr. Corlett”, has by large remained. Here I offer my two cents in response to the second group. More specifically, I argue that Corlett’s challenges to the logic of the two-factor theory, concerning modularity, double dissociation and cognitive penetration, seem to be based on some misunderstandings of the two-factor theory.

KEYWORDS:

• Delusions
• two-factor theory
• modularity
• double dissociation
• cognitive penetration

Acknowledgements

This work was supported by a Chancellor’s International Scholarship from the University of Warwick Graduate School. I thank Johannes Roessler for his invaluable suggestions, thank Ryan McKay for a recent discussion about the two-factor theory, thank R. Ryan Darby for sharing Darby et al.’s (2017) supplementary materials by personal communication, and thank Anthony S. David and the anonymous reviewers for their very helpful comments. I’m responsible for the ideas in it.

Disclosure statement

No potential conflict of interest was reported by the author.

ORCID

Chenwei Nie http://orcid.org/0000-0002-6862-8879

Notes

1. The two-factor theory is a family of accounts. They share this commitment but their views on the details of the two factors may vary. Though it seems that Corlett aims to challenge the two-factor theory in general, only a selection of papers mainly (co-)authored by Coltheart is mentioned, which represents a particular two-factor account. To make this commentary more straightforward, I shall focus on the papers cited by Corlett. But, I think, the arguments and explanations apply to the two-factor theory in general. (Thanks to an anonymous reviewer for helping me clarify this point.)

2. Corlett (2019, p. 171) uses expressions like “factor-2, … is a module”. This might be misconstrued as meaning that the deficit in the belief evaluation system is a module. I think what Corlett actually means by this expression is that the impaired belief evaluation system is a module. Nevertheless, for the sake of argument, this commentary shall follow Corlett’s use.

3. Darby (2019, p. 180) gives a different presentation of the assumptions Corlett argues against: “(1) Modularity of brain functions, (2) Unidirectional flow of information, and (3) Cognitive processes that cannot influence perceptual processes.” He does not include, what I call, Assumption (2) because, I think, his intention is not to give a summary of Corlett’s arguments but to provide “additional data” to support the related arguments (ibid., p. 178). I choose not to elaborate on, what I call, Assumption (3) because, as I shall argue later, the related discussions in both Corlett and Darby’s articles are mainly general statements which seem too ambiguous to be a clear argument against the two-factor theory.

4. Corlett repeatedly claims that the modularity of mind and brain is a problem for the two-factor theory. But it is unclear whether he is also denying that in monothematic delusions the first factor is modular in Coltheart’s sense, that is the first factor is a domain-specific deficit (for a discussion on the empirical evidence, see also McKay, 2019).

5. Nie (2016) further develops the idea that the belief evaluation system involves not only different brain regions but also different functions.

6. It is not clear whether or not subject A in Corlett’s conception needs to be a Capgras patient. In any case, the discussion focuses on subject B.

7. McKay seems to find Corlett’s demand of Capgras patient B confusing. He writes that “this is tantamount to demanding a patient with measles who hasn’t been exposed to the measles virus” (McKay, 2019, p. 186). Here, I’m trying to make plain Corlett’s consideration behind the demand.

8. I think even the single dissociation evidence is not necessary for the two-factor claim. Admittedly, the current two-factor theory is mainly based on the dissociation argument. In these possibilities, the possible two-factor theories would be based on some different arguments from the dissociation argument. Nonetheless, in both cases the central claim obtains. (I’m grateful to an anonymous reviewer for raising the concern about the relationship between the dissociation argument and the two-factor theory.)

9. Thanks to an anonymous reviewer for pressing me to clarify the point in this paragraph.

Additional information

Funding

This work was supported by a Chancellor’s International Scholarship from the University of Warwick Graduate School.