Crespi & Badcock (C&B) envisage a continuum of mentalistic cognition, affect, and behaviour with normality at the centre and autism and psychosis at opposite dysfunctional poles: Autism reflects a bias toward paternally expressed genes and hypo-mentalizing; psychosis reflects a bias toward maternally expressed genes and hyper-mentalizing. This commentary is restricted primarily to the cognitive level of this model.
The implication of C&B's model is that capacities for a suite of mentalizing functions all vary roughly in line with each other as one moves along the continuum. This conception is at odds with findings of dissociations between mentalizing functions. Psychopaths, for example, show good cognitive mentalizing (they understand other people's thoughts well enough to adeptly manipulate and deceive those others) alongside a lack of empathy (i.e., poor affective mentalizing: Blair Reference Blair2005). Of more direct relevance to C&B's model, psychotic people report the opposite pattern: a difficulty with understanding other people's thoughts (i.e., poor cognitive mentalizing) alongside intact affective empathy (Montag et al. Reference Montag, Heinz, Kunz and Gallinat2007). To treat mentalizing as a unidimensional continuum of intercorrelated functions is an oversimplification.
It therefore becomes important to focus on more specific social-cognitive domains: processing of eye-gaze information, using mentalistic language to communicate about minds, theory of mind (ToM), and so forth. Within each domain, the strongest test of C&B's proposal is to compare data collected from autistic and psychotic individuals using similar paradigms. To illustrate, Langdon et al. (Reference Langdon, Corner, McLaren, Coltheart and Ward2006b) used cues of other people's gaze-direction to orient subjects' own attentional shifts and found evidence that automatic orienting to gaze might be heightened in psychotic people. Autism studies of this type are more common, but the findings are mixed. Ristic et al. (2003) found an absence of rapid, automatic orienting to static eye-gaze cues in autistic subjects – broadly the opposite of Langdon et al.'s findings. However, two further studies using procedures more comparable to the Langdon study reported normal reflexive orienting to eye-gaze in autism (Senju et al. Reference Senju, Tojo, Dairoku and Hasegawa2004; Swettenham et al. Reference Swettenham, Condie, Campbell, Milne, Coleman, Frith and Hill2003). While aspects of processing eye-gaze information are clearly impaired in autism, it seems unreasonable to summarily describe autism and psychosis as polar opposites.
Direct comparisons can also be made between studies in which participants described interactions between animated geometric shapes. Several studies have reported a reduced usage of mentalistic language (e.g., the large triangle is encouraging the small triangle) by autistic individuals when describing “ToM scenes” of complex social interactions (Castelli et al. Reference Castelli, Frith, Happé and Frith2002; Klin & Jones Reference Klin and Jones2006; although see Abell et al. Reference Abell, Happé and Frith2000). While autistic individuals under-mentalize, Russell et al. (Reference Russell, Reynaud, Herba, Morris and Corcoran2006) found that paranoid psychotic patients over-mentalize in this paradigm, ascribing intentions to random movements designed as non-ToM control stimuli. Crucially, however, these same patients also under-mentalized in the ToM condition; just like the autistic individuals, they used significantly less mentalistic language than controls to describe animations of socially complex behaviours.
Likewise, Langdon (Reference Langdon, Malle and Hodges2005) found that schizophrenic patients evidenced both under- and over-mentalizing within the same joke-appreciation task. When presented with ToM cartoons that required accurate mental-state inferences in order to get the joke, these patients used less mental-state language than healthy controls and acted as if completely insensitive to the likely contents of the cartoon characters' minds. Yet these same individuals also over-mentalized in a non-mentalistic control condition where they ascribed negative intentions to innocent cartoon characters.
A “hyper-mentalizing” account seems inadequate here. Individuals with psychosis do over-attribute intentions in some contexts, but in others they under-mentalize. One argument might be that stimuli used in ToM tasks activate too many mental-state representations in psychotic people. This would explain the overuse but not the underuse of mentalistic language. Arguably a greater interference between competing mental-state representations might leave patients more confused in ToM conditions. But why should this lead to less mentalistic language, and what causes the greater interference anyway?
An alternative conceptualisation of hyper-mentalizing relates to the inappropriate attribution of self-knowledge to other people. This could explain why psychotic individuals fail to infer those more complex mental states like trickery that typically feature in ToM conditions, described above, as well as in more classic ToM tasks. This argument, however, appears incompatible with the persecutory-deluded people's common complaints that other people do not truly understand them. Why so, if they over-attribute to others what they themselves know? Moreover, in both autism and psychosis, there seems a difficulty with setting aside self-knowledge so as to appreciate another person's unique subjective world. This is the very essence of ToM, so what does it mean to say that one is hypo while the other is hyper?
An alternative viewpoint is provided by Langdon and colleagues (Langdon Reference Langdon, Repacholi and Slaughter2003; Langdon & Coltheart Reference Langdon and Coltheart2001; Langdon et al. Reference Langdon, Coltheart, Ward and Catts2001). They propose that poor ToM task performance in schizophrenia reflects impaired perspective-taking (i.e., a difficulty with entertaining multiple perspectives of the same here-and-now reality). Impaired perspective-taking explains the egocentric projection of psychotic people's own suspicions and biases onto innocent others and ambiguous situations (over-mentalizing) as well as their failure to grasp the interplay between different perspectives in more complex social interactions (under-mentalizing).
In sum, any theory contrasting autism and psychosis must take account of comparable studies of the two disorders rather than relying on general descriptions. Few such comparisons have been conducted, but when relevant data exist, they point to similarities as well as differences. Therefore, regardless of any progress at the genetic or neurological level, we suggest that C&B's mentalizing spectrum must be better specified cognitively. There are differences, for example, among the following:
The capacity to represent “decoupled” mental states (as about yet separate from the world)
The ability to respond to and interpret eye-gaze cues
The tendency to ascribe psychological causation to random or ambiguous stimuli
The ability to appreciate other people's likely thoughts in light of their circumstances (i.e., perspective taking)
Some of these faculties are intact in psychotic people but some are impaired. For some faculties, it might be possible to conceive of a continuum with pathological hypo- and hyper-abilities at opposite poles. For others, it seems unclear how hyper-abilities might be manifested.
