A cognitive examination of compulsive checkers' working memory and inhibitory performance.
PhD thesis, University of Glasgow.
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Checking is one of the most common symptoms observed in Obsessive Compulsive Disorder (OCD) with 50-80% of patients (Antony, Downie, & Swinson, 1998; Henderson & Pollard, 1988; Rasmussen & Eisen, 1988) and an additional ~15% of the general population demonstrating subclinical checking compulsions (Stein et al., 1997). A common finding is that checking actually impairs the memory of those items checked (van den Hout & Kindt, 2003a, 2003b), even though the mechanism underlying checking-related memory impairment has remained elusive. This is a shortcoming that we presently address in a series of short-term memory experiments and attentional tasks comparing high and low checkers (see VOCI; Thordarson et al., 2004). Generally, our memory tasks required stimuli to be remembered in their locations, which was designed to engage the episodic buffer (EB) of working memory (WM) (Baddeley, 2000). The key manipulation was to present an intermediate probe (between encoding and recall) in the form of a resolvable or misleading challenge which questioned an aspect of the encoding set; this was either present or absent, respectively. As expected, misleading probes specifically (Exp. 1, 2, extreme meta-comparison 3 & 9; Harkin & Kessler, 2009; 2011a; Harkin, Rutherford, & Kessler, 2011) and intermediate probes generally (Exp. 4; Harkin & Kessler, 2011a) tap into the inhibitory impairments of high (not low) checkers, which hampers EB functionality and impairs their memory. Indeed, it was only during misleading trials that high checkers made more unnecessary eye movements specifically to empty locations (Exp. 5; Harkin & Kessler, subm). Furthermore, for ecologically valid stimuli high checkers were impaired in inhibiting attention to threatening ‘ON’ states (Tasks 6 & 7; Harkin & Kessler, in press) and in their ability to recall if an appliance was ‘ON’ or ‘OFF’ (Exp. 8; Harkin, Rutherford, & Kessler, 2011). High checkers’ intact performance on baseline no-probe-1 trials excludes a capacity-based explanation of their WM impairments. Overall, confidence measures revealed a general task-independent impairment which was attenuated by an intermediate probe. These findings were then used to create a classification system based upon Executive-Functioning, Binding Complexity and Memory Load (EBL) to explain otherwise discrepant findings from 58 memory studies (Harkin & Kessler, 2011b). Thus, the contribution of this research is not only to (Exp. 1-9) indicate an actual mechanism (i.e., episodic buffer of WM) of memory impairment in checking/OCD but it also provides a new research platform on which to base where we will and will not observe memory impairments in OCD participants. The conclusion summarizes the main findings with respect to the development and maintenance of OCD symptoms, highlights limitations and provides solutions to these through future research.
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