Delusions as Explanations


by Matthew Parrott– Lecturer in the Department of Philosophy at King’s College London

One idea that has been extremely influ­en­tial with­in cog­nit­ive neuro­psy­cho­logy and neuro­psy­chi­atry is that delu­sions arise as intel­li­gible responses to highly irreg­u­lar exper­i­ences. For example, we might think that the reas­on a sub­ject adopts the belief that a house has inser­ted a thought into her head is because she has in fact had an extremely bizarre exper­i­ence rep­res­ent­ing a house push­ing a thought into her head (the case comes from Saks 2007; see Sollberger 2014 for an account of thought inser­tion along these lines). If this were to hap­pen, then delu­sions would arise for reas­ons that are famil­i­ar from cases of ordin­ary belief. A delu­sion­al sub­ject would simply be endors­ing or tak­ing on board the con­tent of her experience.

However the notion that a delu­sion is an under­stand­able response to an irreg­u­lar exper­i­ence need not be con­strued along the lines of a sub­ject accept­ing the con­tent of her exper­i­ence. Over a num­ber of years, Brendan Maher advoc­ated an influ­en­tial altern­at­ive pro­pos­al, accord­ing to which an indi­vidu­al adopts a delu­sion­al belief because it serves as an explan­a­tion of her ‘strange’ or ‘sig­ni­fic­ant’ exper­i­ence (see Maher 1974, 1988, 1999). Crucially, for Maher, the con­tent of the subject’s exper­i­ence is not identic­al to the con­tent of her delu­sion­al belief. Rather, the lat­ter is determ­ined in part by con­tex­tu­al factors, such as cul­tur­al back­ground or what Maher calls ‘gen­er­al explan­at­ory sys­tems’ (cf. 1974). Maher’s approach is often referred to as the ‘explan­a­tion­ist’ approach to under­stand­ing delu­sions (Bayne and Pacherie 2004).

Explanationist accounts have been espe­cially pop­u­lar with respect to the Capgras delu­sion that one’s friend or rel­at­ive is really an imposter (e.g., Stone and Young 1997) and delu­sions of ali­en con­trol (e.g., Blakemore, et. al. 2002). Yet, des­pite their pre­val­ence, the explan­a­tion­ist approach has been called into ques­tioned by a num­ber of philo­soph­ers on the grounds that delu­sions are quite obvi­ously very bad explanations.

For instance, Davies and col­leagues argue:

‘The sug­ges­tion that delu­sions arise from the nor­mal con­struc­tion and adop­tion of an explan­a­tion for unusu­al fea­tures of exper­i­ence faces the prob­lem that delu­sion­al patients con­struct explan­a­tions that are not plaus­ible and adopt them even when bet­ter explan­a­tions are avail­able. This is a strik­ing depar­ture from the more nor­mal think­ing of non-delusional sub­jects who have sim­il­ar exper­i­ences.’ (Davies, et. al. 2001, pg. 147; but see also Bayne and Pacherie 2004, Campbell 2001, Pacherie, et. al. 2006)

Indeed, since delu­sions strike most of us as highly implaus­ible, it is hard to see how they could explain any exper­i­ence, no mat­ter how unusu­al. So if we want to under­stand delu­sion­al cog­ni­tion along Maher’s lines, we will need to cla­ri­fy the cog­nit­ive trans­ition from anom­al­ous exper­i­ence to delu­sion­al belief in a way that illu­min­ates how it could be a genu­inely explan­at­ory transition.

In what fol­lows, I would like to dis­tin­guish three dis­tinct ways in which a delu­sion­al belief might be thought to be explan­at­or­ily inad­equate, each of which I think poses a dis­tinct chal­lenge for the explan­a­tion­ist approach.

The first con­cerns the phe­nom­en­al char­ac­ter of a delu­sion­al subject’s anom­al­ous exper­i­ence. Maher claims that the strange exper­i­ences we find in cases of delu­sion ‘demand’ explan­a­tions. But why is that? If the exper­i­ences that give rise to delu­sions do not them­selves rep­res­ent highly unusu­al states of affairs (as Maher seems to think), what is it about them that calls for or ‘demands’ an explan­a­tion? And does the par­tic­u­lar phe­nom­en­al char­ac­ter of a ‘strange’ exper­i­ence ‘demand’ a spe­cif­ic form of explan­a­tion, or are all ‘strange’ exper­i­ences rel­at­ively equal when it comes to their demands? The chal­lenge for the explan­a­tion­ist is to cla­ri­fy the phe­nom­en­al char­ac­ter of a delu­sion­al subject’s anom­al­ous exper­i­ence in such a man­ner that makes clear how it could be the explanad­um of a delu­sion. Let’s call this the Phenomenal Challenge.

I actu­ally think some very influ­en­tial neuro­psy­cho­lo­gic­al accounts have dif­fi­culty with the Phenomenal Challenge. To briefly take one example, Ellis and Young (1990) pro­posed that the Capgras delu­sion arises because of a lack of respons­ive­ness to famil­i­ar faces in the auto­nom­ic nervous sys­tem. In non-delusional sub­jects, an exper­i­ence of a famil­i­ar face is asso­ci­ated with an affect­ive response in the auto­nom­ic nervous sys­tem, but Capgras sub­jects fail to have this response. Ellis and Young’s the­ory pre­dicted that there would be no sig­ni­fic­ant dif­fer­ence in the skin con­duct­ance responses of Capgras sub­jects when they are shown famil­i­ar verses unfa­mil­i­ar faces, which has sub­sequently been con­firmed by a num­ber of stud­ies. Thus it seems there is good evid­ence that a typ­ic­al Capgras subject’s auto­nom­ic nervous sys­tem is not sens­it­ive to famil­i­ar faces.

This seems prom­ising but I don’t think it answers the Phenomenal Challenge because it doesn’t tell us any­thing about what a Capgras subject’s exper­i­ence of a face is like. As John Campbell notes, ‘the mere lack of affect does not itself con­sti­tute the perception’s hav­ing a par­tic­u­lar con­tent.’ (2001, pg. 96) Moreover, indi­vidu­als are not nor­mally con­scious of their auto­nom­ic nervous sys­tem (see Coltheart 2005). So it isn’t clear how dimin­ished sens­it­iv­ity with­in that sys­tem con­sti­tutes an exper­i­ence that ‘demands’ an explan­a­tion involving imposters. To really under­stand why an anom­al­ous exper­i­ence of a famil­i­ar face calls for a delu­sion­al explan­a­tion, we need to get a bet­ter sense on what that exper­i­ence is like.

A second worry raised in the pre­vi­ous pas­sage is that delu­sion­al sub­jects adopt delu­sion­al explan­a­tions ‘even when bet­ter explan­a­tions are avail­able’. Why does this hap­pen? Why does a delu­sion­al sub­ject select an inferi­or hypo­thes­is from the set of those avail­able to her? Let’s call this the Abductive Challenge.

To illus­trate, let’s stick with Capgras. The explan­a­tion­ist pro­pos­al is that a sub­ject adopts the belief that her friend has been replaced by an imposter in order to explain some odd exper­i­ence. But even if we sup­pose the imposter hypo­thes­is is empir­ic­ally adequate, it is highly unlikely to be the best explan­a­tion avail­able. As Davies and Egan remark, ‘one might ask wheth­er there is an altern­at­ive to the imposter hypo­thes­is that provides a bet­ter explan­a­tion of the patient’s anom­al­ous exper­i­ence. There is, of course, an obvi­ous can­did­ate for such a pro­pos­i­tion.’ (2013, pg. 719) In fact, there seems to be a num­ber of bet­ter avail­able hypo­theses; for example, that one has suffered brain injury or any hypo­thes­is that appealed to more famil­i­ar changes affect­ing facial appear­ance, such as hair-style or illness.

Put simply, the Abductive Challenge is that even if we assume the cog­nit­ive trans­ition from unusu­al exper­i­ence to delu­sion involves some­thing like abduct­ive reas­on­ing or infer­ence to the best explan­a­tion, delu­sion­al sub­jects select poor explan­a­tions instead of bet­ter avail­able altern­at­ives. The explan­a­tion­ist needs to tell us why this hap­pens (for some attempts see Coltheart et. al. 2010, Davies and Egan 2013, McKay 2012, Parrott and Koralus, 2015).

The final chal­lenge for explan­a­tion­ism is, in my view, the most prob­lem­at­ic. In the above pas­sage, Davies and col­leagues remark that delu­sions are extremely implaus­ible. Along these lines, we might nat­ur­ally won­der why a sub­ject would even con­sider one to be a can­did­ate explan­a­tion of her unusu­al exper­i­ence. Why would she not instead imme­di­ately rule out a delu­sion­al hypo­thes­is on the grounds that it is far too implaus­ible to be giv­en ser­i­ous con­sid­er­a­tion? This con­cern is echoed by Fine and colleagues:

‘They explain the anom­al­ous thought in a way that is so far-fetched as to strain the notion of explan­a­tion. The explan­a­tions pro­duced by patients with delu­sions to account for their anom­al­ous thoughts are not just incor­rect; they are non­starters. Appealing to the notion of explan­a­tion, there­fore, does not cla­ri­fy how the delu­sion­al belief comes about in the first place because the explan­a­tions of the delu­sion­al patients are noth­ing like explan­a­tions as we under­stand them.’ (Fine, et. al. 2005, pg. 160)

The task of explain­ing some tar­get phe­nomen­on demands cog­nit­ive resources and the idea that delu­sions are explan­at­ory ‘non­starters’ means that they nor­mally would be imme­di­ately rejec­ted. When engaged in an explan­at­ory task, we know that a per­son con­siders only a restric­ted set of hypo­theses and it seems quite nat­ur­al to exclude ones that are incon­sist­ent with one’s back­ground know­ledge. Since delu­sions seem to be in con­flict with our back­ground know­ledge, this is per­haps why we find it dif­fi­cult to under­stand how someone could think a delu­sion is even poten­tially explan­at­ory (for fur­ther dis­cus­sion, see Parrott 2016).

So why do sub­jects con­sider delu­sion­al explan­a­tions as can­did­ate hypo­theses? This is the final chal­lenge for the explan­a­tion­ist. Let’s call it the implaus­ib­il­ity chal­lenge. Notice that where­as the abduct­ive chal­lenge asks why a sub­ject even­tu­ally adopts one hypo­thes­is instead of anoth­er from among a fixed set of avail­able altern­at­ives, the implaus­ib­il­ity chal­lenge is more gen­er­al. It asks where these hypo­theses, the ones sub­ject to fur­ther invest­ig­a­tion, come from in the first place.

Can these three chal­lenges be over­come? I am optim­ist­ic and have tried to address them for the case of thought inser­tion (see Parrott forth­com­ing). However, I also think much more work needs to be done.

First, as I men­tioned above, it is not clear that we have a good under­stand­ing of what it is like for an indi­vidu­al to have the sorts of exper­i­ences we think are implic­ated in many cases of delu­sion. Without such under­stand­ing, I think it is hard to see why some exper­i­ences make demands on a person’s cog­nit­ive explan­at­ory resources. I also sus­pect that under­stand­ing what vari­ous anom­al­ous exper­i­ences are like might shed more light on why delu­sion­al indi­vidu­als tend to adopt very sim­il­ar explanations.

Second, I think that address­ing the implaus­ib­il­ity chal­lenge requires us to obtain a far bet­ter under­stand­ing of how hypo­theses are gen­er­ated than we cur­rently have. In both delu­sion­al and non-delusional cog­ni­tion, an explan­at­ory task presents a com­pu­ta­tion­al prob­lem. Which can­did­ate hypo­theses should be selec­ted for fur­ther empir­ic­al test­ing? Although I have sug­ges­ted that epi­stem­ic­ally impossible hypo­theses are nor­mally ruled out, that doesn’t tell us how can­did­ates are ruled in. Plausibly, there is some selec­tion function(s) that chooses can­did­ate explan­a­tions of a tar­get phe­nomen­on, but, as Thomas and col­leagues note, we have very little sense of how this might work:

‘Hypothesis gen­er­a­tion is a fun­da­ment­al com­pon­ent of human judg­ment. However, des­pite hypo­thes­is generation’s import­ance in under­stand­ing judg­ment, little empir­ic­al and even less the­or­et­ic­al work has been devoted to under­stand­ing the pro­cesses under­ly­ing hypo­thes­is gen­er­a­tion (Thomas, et. al. 2008, pg. 174).

The implaus­ib­il­ity chal­lenge strikes me as espe­cially puzz­ling because I think we can eas­ily see that cer­tain strategies for hypo­thes­is gen­er­a­tion would be bad. For instance, it wouldn’t gen­er­ally be good to con­sider hypo­theses only if they have a pri­or prob­ab­il­ity above a cer­tain threshold, because a hypo­thes­is with a low pri­or prob­ab­il­ity might best explain a new piece of evidence.

Delusional cog­ni­tion raises quite a few deep and inter­est­ing ques­tions, many of which bear on how we think about belief form­a­tion and reas­on­ing. And I have only scratched the sur­face when it comes to the kinds of puzzles that arise when we start think­ing about the ori­gins of delu­sion. But I hope that dis­tin­guish­ing these explan­at­ory chal­lenges will help us in think­ing about the ques­tions which need to be pur­sued if we are to assess the plaus­ib­il­ity of the explan­a­tion­ist strategy.



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