Conditional reasoning in Asperger's syndrome and depersonalization disorder.

Conditional reasoning premises can be systematically manipulated to elicit specific response patterns. This is useful for investigating the reasoning style of people who report clinical symptoms. We administered a standardized conditional reasoning task to 16 participants with a diagnosis of Asperger's syndrome (AS), 16 participants with a diagnosis of depersonalization disorder (DPD), and 32 intelligence-quotient-matched controls. Premises were manipulated for a) context, with some being embedded within extra statements, and b) content, neutral or emotional. Both the AS and DPD participants were less likely to incorporate exceptions to the given premises than the controls, indicating difficulties with mental flexibility, although this effect was less marked in the DPD group. It seems the AS participants were also less influenced than the controls by statements that highlight possible alternative consequences. However, this effect was less robust than that observed with statements detailing exceptions, suggesting it may be because of general problems with executive function rather than difficulties in processing contextual information. We did not observe the expected difference between the DPD participants and the controls when reasoning with emotional premises. Overall, these data suggest that the DPD and AS participants have distinct reasoning styles, which may be of use for interventions based on cognitive change.