Contrary to the cliché widespread among intellectuals of ordinary people as easily deceived simpletons, humans have an evolutionary rooted distrust of what others say., of all things, this "epistemic vigilance" may be the foundation for delusions

Delusions as Epistemic Hypervigilance. Ryan McKay, Hugo Mercier. Current Directions in Psychological Science, March 8, 2023. https://doi.org/10.1177/09637214221128320

Abstract: Delusions are distressing and disabling symptoms of various clinical disorders. Delusions are associated with an aberrant and apparently contradictory treatment of evidence, characterized by both excessive credulity (adopting unusual beliefs on minimal evidence) and excessive rigidity (holding steadfast to these beliefs in the face of strong counterevidence). Here we attempt to make sense of this contradiction by considering the literature on epistemic vigilance. Although there is little evolutionary advantage to scrutinizing the evidence our senses provide, it pays to be vigilant toward ostensive evidence—information communicated by others. This asymmetry is generally adaptive, but in deluded individuals the scales tip too far in the direction of the sensory and perceptual, producing an apparently paradoxical combination of credulity (with respect to one’s own perception) and skepticism (with respect to the testimony of others).

Epistemic Vigilance

A set of putative cognitive mechanisms serves a function of epistemic vigilance: to evaluate communicated information so as to accept reliable information and reject unreliable information (Sperber et al., 2010). The existence of these mechanisms has been postulated on the basis of the theory of the evolution of communication (e.g., Maynard Smith & Harper, 2003; Scott-Phillips, 2008). For communication between any organisms to be stable, it must benefit both those who send the signals (who would otherwise refrain from sending them) and those who receive them (who would otherwise evolve to ignore them). However, senders often have incentives to send signals that benefit themselves but not the receivers. As a result, for communication to remain stable, there must exist some mechanism that keeps signals, on average, reliable. In some species, the signals are produced in such a way that it is simply impossible to send unreliable signals—for instance, if the signal can be produced only by large or fit individuals (see, e.g., Maynard Smith & Harper, 2003). In humans, however, essentially no communication has this property.1 It has been suggested instead that humans keep communication mostly reliable thanks to cognitive mechanisms that evaluate communicated information, rejecting unreliable signals and lowering our trust in their senders—mechanisms of epistemic vigilance.

To evaluate communicated information, mechanisms of epistemic vigilance process cues related to the content of the information (Is it plausible? Is it supported by good arguments?) and to its source (Are they honest? Are they competent?). A wealth of evidence shows that humans possess such well-functioning mechanisms (for review, see, e.g., Mercier, 2020), that they are early developing (being already present in infants or toddlers; see, e.g., Harris & Lane, 2014), and that they are plausibly universal among typically developing individuals. Crucially for the point at hand, these epistemic vigilance mechanisms are specific to communicated information. Our own perceptual mechanisms evolved to best serve our interests, and there are thus no grounds for subjecting their deliverances to the scrutiny that must be deployed for other individuals.

There is now a large amount of evidence that people systematically discount information communicated by others. This tendency has often been referred to as egocentric discounting (Yaniv & Kleinberger, 2000), and it has been observed in a wide variety of experimental settings (for a review, see Morin et al., 2021). For instance, in advice-taking experiments, participants are asked a factual question (e.g., What is the length of the Nile?), provided with someone else’s opinion, and given the opportunity to take this opinion into account in forming a final estimate. Overall, participants put approximately twice as much weight on their initial opinion as on the other participant’s opinion, even when they have no reason to believe the other participant less competent than themselves (Yaniv & Kleinberger, 2000).

The discounting of others’ opinions can be overcome if we have positive reasons to trust them or if they present good arguments—in particular, if our prior opinions are weak (see, e.g., Mercier & Sperber, 2017). However, in the absence of such positive reasons, discounting is a pervasive phenomenon. There is no such systematic equivalent when it comes to perception. Although in some cases we can or should learn to doubt what we perceive (e.g., when attending to the reminder that “objects in mirror are closer than they appear” while driving), this is typically an effortful process with uncertain outcomes. In visual perception, for example, models in which the observer behaves like an optimal Bayesian learner have proven very successful at explaining participants’ behavior (e.g., Geisler, 2011). Even if there are deviations from this optimal behavior (e.g., Stengård & van den Berg, 2019), they do not take the form of a systematic tendency to favor our priors over novel information.

There is thus converging evidence (a) that humans process communicated information differently than information they acquire entirely by their own means and (b) that the former is systematically discounted by default (i.e., in the absence of reasons to behave otherwise, such as reasons to believe the source particularly trustworthy or competent). This, however, leaves open significant questions of great relevance for the present argument. In particular, to what stimuli does epistemic vigilance apply to? Presumably, epistemic vigilance evolved chiefly to process the main form of human communication: ostensive communication, which includes verbal communication but also many nonverbal signals (from pointing to frowning). Related mechanisms apply to other types of communication, such as emotional communication (Dezecache et al., 2013).

What of behaviors that have no ostensive function (e.g., eating an apple) or even aspects of our environment that might have been modified by others (e.g., a book found on the coffee table)? Although such stimuli should not trigger epistemic vigilance by default, they may under some circumstances. One might interpret a friend eating an apple as an indication that the friend has followed health advice to eat more fruit, or one could interpret one’s spouse’s placement of a book on a table as an invitation to read it—whether it was so intended or not. The behavior might then be discounted: We might suspect our friend of eating the apple only for our benefit while privately gorging on junk food.

Other cognitive mechanisms, more akin to strategic reasoning, but bound to overlap with epistemic vigilance, must process noncommunicative yet manipulative information (on the definition of communication vs. manipulation or coercion, see Scott-Phillips, 2008). A detective should be aware that some clues might have been placed by the criminal to mislead her. In some circumstances, therefore, epistemic vigilance and related mechanisms might apply even to our material environments, instead of applying only to straightforward cases of testimony. Still, epistemic vigilance should always apply to testimony, whereas it should apply to perception only under specific circumstances, such that the distinction between these two domains (testimony vs. perception) remains a useful heuristic.

How might these considerations inform our understanding of delusions? Whereas in healthy individuals the scales are adaptively tipped in favor of trusting the perceptual over the ostensive, this imbalance may be maladaptively exacerbated in delusions (Fig. 1). This could be for at least two complementary reasons: Sensory or perceptual evidence may be overweighted, and testimonial evidence may be underweighted. We review each of these possibilities in turn.