Atypical Minds: the Cognitive Science of Difference and Potentialities
Cognitio 2015
Young researchers conference in cognitive science
Montréal, June 8th, 9th and 10th 2015
Why Psychosis is Unique
Christopher Parker.
Bortolotti (2009; 2012; 2014) argues that psychotic delusion is not a unique cognitive condition; rather, it is an extreme pole on a continuum of irrationality that includes mundane phenomena such as prejudice and superstition. Similarly, psychiatric researchers (cited below) have presented evidence that psychotic symptomatology is continuous across clinical and nonclinical populations. These ideas suggest a flaw in the conventional view of psychosis as characterized by unique detachment from and resistance to reality, a characterization also implied by the DSM diagnostic criteria. I defend the conventional view, arguing that Bortolotti’s continuum hypothesis fails to consider the subjective affective and perceptual context in which psychosis occurs. Once delusions are viewed in that context, it is clear that they are unique cognitive phenomena.
Consider the evidence in favor of the continuum hypothesis. Recent surveys of nonclinical populations have repeatedly shown that hallucinatory experiences are relatively widespread (for reviews see Morrison, 2001; Johns and van Os, 2001). The same may be true of delusional beliefs. Peters, Joseph, and Garety (1999) compared responses of clinical and nonclinical populations to a survey of common delusional themes – including paranoia, grandiosity, reference, control, etc. – and found that a significant number of nonclinical respondents endorsed more delusional contents than the clinical mean. However, they found that the extent to which the endorsed contents were rated as subjectively distressing, preoccupying, and the degree of commitment expressed toward them is predictive of clinical psychosis. Taken together, these factors suggest that a distinction between nonclinical symptomatology and actual psychosis is the degree to which one’s symptoms become are to one’s life.
Granting that this evidence is suggestive of a continuum of psychosis – with those who are relatively unaffected by their symptoms removed from the clinical extreme of those who are wholly preoccupied by them – one still cannot infer Bortolotti’s hypothesis from the evidence alone. It does not follow from the fact that both clinical and nonclinical populations experience similar cognitive phenomena, that there is no clean distinction between those groups. Indeed, it should be clear that preoccupation with some delusional theme is insufficient for clinical psychosis, even if combined with high levels of distress and commitment. This is because clinical delusions are almost always self-involving. Psychotic individuals do not just believe that telepathic communication is possible, as 60% of Peters, Joseph, and Garety’s (1999) nonclinical population did; rather, they tend to believe that they are involved in telepathic communication. This is not surprising. As Maher (2006) argues, hallucinatory experiences are frequently co-occurrent with, and provide motivation for, delusional beliefs. The personal nature of hallucinatory experience provides a logical connection to self-involving delusion.
Now it must be asked why some people are able to shrug off hallucinatory experiences, while others have profound responses to them. I propose that hallucinations motivate delusions when they are experienced against the backdrop of profound affective disturbance. Kapur (2003) has argued that an important causal antecedent to psychosis is failure to selectively suppress attention, leading one to experience irrelevant stimuli as hyper-salient. This experience is both affectively charged and anxiety inducing, as evidenced by first-person descriptions of the psychotic prodrome and by the documented correlation of psychosis with anxiety (e.g. Garety et al, 2005; Freeman, 2007). It is against the baseline of affective disorder that hallucinatory experiences take on profound subjective significance, and this explains how the frequently bizarre contents of psychotic delusion achieve verisimilitude for the deluded and are strongly endorsed. Thus, once the affective origin of psychosis is appreciated, it can be seen that the psychotic does inhabit an idiosyncratic world of experience and belief. Psychotic delusion is, therefore, a unique cognitive phenomenon.