Abstract
People with obsessive-compulsive disorder (OCD) commonly report doubt and uncertainty and feel driven to perform repetitive behaviours and rituals. Neuropsychological accounts of obsessive-compulsive (OC) behaviours suggest that dysfunction in cognitive processing may underpin such symptomology. Selective attention and long-term memory have been proposed as areas of cognition in which processing may be altered in OCD. However, although the weight of evidence points to possible dysfunction in these areas, the results of previous research examining both have been mixed. This thesis argues that inconsistencies in such research might be attributable to the use of the unsuitable methodological approaches, an inconsistent use of symptom-salient stimuli in experiments and a lack of acknowledgement of the heterogeneity of OCD or the impact of comorbidities. The studies presented here adopted methodological approaches which are novel in OCD research, with the aim of providing more nuanced accounts of OC cognition. Four studies are reported which examined how far altered OC selective attention and long-term memory, and particularly that of Checkers, may be rooted in the operation the same mechanism – bias towards distracting and symptom-salient stimuli. Studies 1, 2 and 3 used selective attention visual search paradigms with inter-trial components, based on the priming of pop-out (PoP) design. Study 4 was a comprehensive examination of verbal long-term memory, including remember/know memory, using the CID-R paradigm. All four used non-clinical OC populations, in line with arguments that clinical OCD only accounts for a minority of individuals who display OC symptomology. Study 1 (N=28) looked to establish initial evidence of possible selective attention and attentional bias differences between a homogenous OC group and Controls. Study 2 (N=43) and Study 3 (N=46) then built on these findings, examining possible differences between Checker and Non-Checker groups with the presentation of symptom-salient and emotional stimuli. Finally, Study 4 (N=59) looked to assess how far possible altered attention and bias among Checkers would also be apparent in dysfunction and bias in Checker verbal long-term memory. This study also used symptom-salient stimuli, and recruited Washer and generalised OC participants for comparison with Checkers. Key findings were as follows. In Study 1, OC participants demonstrated, firstly, a deficit in selective attention in the PoP task and, secondly, attentional bias towards distractor stimuli in particular inter-trial sequences. However, when the first of these findings was followed-up in Study 2 using Checker and Non-Checker populations and emotional pictures added to the PoP paradigm, group differences evident in Study 1 were eliminated. But in Study 3, which further examined the second finding of Study 1, evidence of attentional bias in Checkers towards emotional and symptom-salient picture stimuli when inter-trial sequences were examined. Finally, in Study 4, Checkers demonstrated bias towards checking-salient word targets when compared with Controls, and accurate hit rate performance for checking words even though they were significantly more reliant on familiarity with stimuli ('know' memory) than firm recollection ('remember' memory). Effect sizes for group difference findings across the studies were large. The findings provide novel and nuanced evidence of the key roles of bias and emotion in the operation of OC cognition and the make-up of Checker symptomology, and further highlight the value of using non-clinical participants in OC research.