Larger than life: overestimation of object size is moderated by personal relevance in obsessive-compulsive disorder

Along with other cognitive biases overestimation of threat (OET) has been implicated in the pathogenesis of obsessive-compulsive disorder (OCD). The present study investigated whether OET would not only manifest in cognitive distortions but, also in overestimations of the object size of disorder-related visual objects.

A total of 65 participants with OCD and 55 healthy controls who were recruited via OCD online forums underwent an incidental learning paradigm consisting of two blocks. In Block 1, participants were asked to rate the valence and the personal relevance for individual OCD concerns of 40 pictures which varied in size. Differences in size, however, were not explicitly communicated to the participants. Stimuli were selected from four categories: 1. neutral, 2. fear-related but OCD-unrelated, 3. washing (OCD-related), and 4. checking (OCD-related). In Block 2, participants were asked to recollect the original size of each stimulus (depicted as a small thumbnail) on a seven point scale.

Whereas few group differences emerged for pre-defined OCD items, OCD-relevant items (individual judgments) were judged as significantly larger by patients with OCD relative to controls. The opposite pattern emerged for neutral items.

The sample was recruited via online forums and had probable but not externally validated diagnoses of OCD. No psychiatric control group was recruited.

The present study indicates that OET may extend to neuropsychological tasks. Further research is needed to pinpoint whether OET occurs at the level of encoding suggesting a perceptual bias and/or occurs at the level of retrieval suggesting a memory bias.