Empiricist models explain delusional beliefs by identifying the abnormal experiences which ground them. Recently, this strategy has been adopted to explain the false body size beliefs of anorexia nervosa patients. As such, a number of abnormal experiences of body size which patients suffer from have been identified. These oversized experiences convey false information regarding the patients’ own bodies, indicating that they are larger than reality. However, in addition to these oversized experiences, patients are also exposed to significant evidence suggesting their bodies are in fact thin. This situation poses a conundrum: why do patients appear strongly influenced by the former kinds of evidence while the latter has little effect? To solve this conundrum, I suggest a two-factor account. First, I discuss research on the biases patients exhibit in how they gather, attend to and interpret evidence related to their own body size. Such biases in evidence treatment, I suggest, cause oversized experiences to be sought out, attended to and accepted, while veridical body size experiences are ignored or explained away. These biases constitute the second factor for this empiricist model, accounting for the unwarranted conviction with which these beliefs are held. Finally, in line with recent research into self-deception, I propose that, paradoxically, these biases in evidence treatment arise from patients’ own desires.
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Evidence of this comes from figural drawing scale experiments: participants are asked to select body size silhouettes that match both their current and ideal body sizes, with the difference in size taken to be an indication of “body dissatisfaction” (Moussally et al. 2017).
This isn't to say that the oversized experiences discussed are in no way related to the deficits in interoceptive processing that have been uncovered. A link between these two forms of dysfunction may emerge, though it’s not yet clear what this link might be.
Unlike with the other forms of oversized experiences, most of the research into spontaneous mental imagery in ED has been conducted on BN, rather than AN, patients (cf. Cooper et al. 1998). This lends further support to the possibility that the model discussed here might apply to a number of eating disorders (see Sect. 4).
It might be that patients also experience their body size accurately through direct visual perception, though this is a source of some contention. While some patients claim they (directly) see themselves as thin, others claim the opposite (Espeset et al. 2011). Based on evidence from mirror exposure research, it has recently been argued that AN patients’ direct perception of their bodies must be veridical (Gadsby 2017c, 27). Nevertheless, this is still an open question (cf. Mohr et al. 2016).
Within delusion literature, the maintenance problem just posed is sometimes distinguished from the adoption problem, which requires an explanation for why the abnormal content was adopted as belief in the first place (Davies and Egan 2013). That said, I won’t delve into the specifics of this distinction here as, although interesting, it’s orthogonal to my central thesis (cf. Gadsby 2017b, 501–503).
This example coheres with research into the confabulatory practices of delusional patients, who often arrive at patently implausible explanations for evidence which conflicts with their delusional beliefs (Langdon and Bayne 2010, 323).
See Holmes and Mathews (2010, 354–355) for a discussion of some different hypotheses for why clinical patients might come to interpret spontaneous mental imagery as veridical.
An interesting point arises here regarding whether the relationship between desires and biased hypothesis testing must be consciously mediated by a belief that this form of hypothesis testing will avoid the relevant costly error (Mele 2001, 31–32, 42–46). In some cases, such as the mentioned excerpt, patients clearly are aware that certain evidence treatment practices (i.e. body checking) will aid in avoiding undesirable situations. Yet this needn’t be the case with all instances of biased hypothesis testing. For example, it seems less likely that attentional and interpretational biases are consciously mediated and indeed the FTL model allows that much of this biasing is “automatic and inflexible … reflecting the operation of evolved cognitive adaptations to a range of biologically significant problems” (Friedrich 1993, p. 317).
It’s worth highlighting that this story would markedly differ from the discussed hypothesis regarding affordance salience in AN. While that hypothesis claims all size-determined affordances have increased salience (due to patients’ mental preoccupation with body size related themes), the proposed self-deception hypothesis suggests a particular subset of size-determined affordances (those likely to reinforce beliefs about being overweight) would exhibit increased salience. Such a bias would manifest in patients attending to affordances they believed their bodies were too large for.
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Thanks to Peter Clutton and Jakob Hohwy for feedback on earlier drafts. This research was supported by an Australian Government Research Training Program (RTP) Scholarship.
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Gadsby, S. Self-Deception and the Second Factor: How Desire Causes Delusion in Anorexia Nervosa. Erkenn 85, 609–626 (2020). https://doi.org/10.1007/s10670-018-0039-z