Inductive and deductive reasoning in Obsessive-Compulsive Disorder

Inductive and deductive reasoning in Obsessive-Compulsive Disorder Janice H. Liew (j.liew@psy.unsw.edu.au) School of Psychology, University of New South Wales Sydney, 2052, Australia Brett K. Hayes (b.hayes@unsw.edu.au) School of Psychology, University of New South Wales Sydney, 2052, Australia Abstract This study examined the hypothesis that individuals with obsessive-compulsive disorder (OCD) show a selective deficit in inductive reasoning but are unimpaired in their ability to make deductive inferences. 100 participants from an analog sample made inductive or deductive inferences about arguments that differed according to causal consistency and validity. They also completed a task examining sensitivity to the implications of diverse evidence in induction. Participants who were high or low on obsessive- compulsive symptoms showed similar patterns of induction based on causal knowledge and similar patterns of deduction. However, those with the highest level of OCD symptoms showed less of a preference for diverse evidence when evaluating inductive arguments, compared to those with the lowest level of symptoms. This difference was found across both OCD-relevant and OCD- neutral items, and persisted when the effects of group differences in general ability were controlled. These results indicate that both inductive reasoning based on background knowledge and deductive reasoning are intact in individuals with high OCD-traits but the use of inductive heuristics such as evidence diversity is impaired. Keywords: inductive reasoning, deductive psychopathology, cognitive neuropsychiatry reasoning, Introduction Obsessive-compulsive disorder (OCD) is characterized by the experience of unwanted, repetitive intrusions in the form of thoughts, impulses or images. These obsessions are often accompanied by compulsions (repetitive behaviors or mental acts) that represent attempts to reduce or neutralize the marked distress that the obsessions cause. A variety of biological, cognitive and social factors affect the onset and maintenance of OCD symptoms (Riggs & Foa, 1993). Recently, a number of theoretical accounts have suggested that deficits in reasoning contribute to OCD symptomatology. Some of these accounts suggest that people with OCD have difficulty in reasoning about uncertain or probabilistic information (O’Connor, 2002; Pelissier & O'Connor, 2002); that is, they show a deficit in some forms of inductive reasoning. These accounts suggest that this is a global deficit, such that people with OCD show poorer inductive reasoning compared to controls across a range of stimulus materials and content domains. Moreover, this impairment in inductive reasoning is thought to be found together with a relatively intact ability to reason deductively. Unlike induction, deduction involves the evaluation of arguments that are certain to be either valid or invalid on the basis of logical rules (Heit, Rotello, & Hayes, A review of the empirical evidence however, reveals only mixed support for this “impaired induction but spared deduction” account of OCD. In support of this account, Pelissier and O'Connor (2002) found that individuals with OCD had more difficulty than controls in drawing plausible probabilistic conclusions from a set of verbal statements about everyday situations. This impairment in inductive reasoning was found together with apparently intact deductive reasoning, as measured by performance on the Wason Selection Task and ability to discriminate between valid and invalid verbal syllogisms. Moreover, this pattern was found with stimulus materials that had little connection with the content of OCD patients’ obsessions. Other work however, has suggested that the reasoning deficit in OCD extends to deduction as well as induction. For example, Simpson, Cove, Fineberg, Msetfi, and Ball (2007) found that people with OCD were poorer than controls at discriminating between logically valid and logically invalid syllogisms with OCD-neutral content. This mixed pattern of evidence reflects, at least in part, a general problem with the methods used in previous attempts to examine inductive and deductive reasoning in people with OCD. These studies have made little attempt to match tasks that ostensibly assess inductive and deductive reasoning on dimensions such as overall task difficulty, stimulus content and task familiarity. Hence, differences in performance between nominally inductive and deductive tasks may actually reflect task-specific characteristics rather than in the cognitive processes that underlie inductive and deductive reasoning. A major aim of the current studies was to re-examine inductive and deductive reasoning in those with OCD- related traits and controls, using a method that addressed this major limitation of previous work. The general approach is patterned after Rips (2001) and Heit and Rotello (2010) who asked university undergraduates to evaluate a set of verbal arguments that varied in both logical validity and inductive plausibility. Crucially, different groups evaluated the set of arguments on the basis of logical necessity (deduction condition) or the overall plausibility (induction condition) of the conclusions. Another important aim was to carry out a more exhaustive examination of possible deficits in inductive reasoning in those with OCD-related traits. A review of