The role of working memory in compulsive checking and OCD: A systematic classification of 58 experimental findings
Highlights
► We provide a novel system to explain otherwise contradictory OCD memory research. ► We extend the recent executive basis of OCD memory impairment argument. ► This includes Executive-Functioning, Binding Complexity and Memory Load. ► Therefore, OCD memory impairment is not primarily an issue of capacity and/or domain. ► We then compare the EBL system to other models of memory impairment in OCD.
Introduction
Despite a large body of research the evidence for memory impairments in OCD is described as mixed at best (Hermans, Engelen, Grouwels, Joos, Lemmens, & Pieters, 2008). For example, there are inconsistent findings regarding a general mnestic deficit (e.g. Tallis, 1997 vs. MacDonald et al., 1997, McNally and Kohlbeck, 1993), verbal memory (e.g., intact: Henseler, Gruber, Kraft, Krick, Reith, & Falkai, 2008 vs. deficit: Tuna, Tekcan, & Topcuoglu, 2005) and generally affected visuospatial memory (Hermans et al., 2008, Mataix-Cols et al., 1999, Muller and Roberts, 2005). We attribute this to the traditional pursuit of OCD memory impairment as one of the general capacity and/or domain specific deficits (visuospatial vs. verbal).
In contrast, a body of research indicates a more subtle relationship, with memory impairments secondary to executive dysfunction (Greisberg & McKay, 2003). If a memory task taps into a dysfunctional component of executive functioning, memory impairment will follow (see Table 1). In this understanding, it is executive deficits in conjunction with task requirements that differentiate memory functioning in OCD from controls (Olley, Malhi, & Sachdev, 2007). This review aims at providing a more precise level of explanation based on Baddeley's extended working memory model (2000) that offers an optimal platform for relating executive functions to representations in memory.
Section snippets
A working-memory explanation
Baddeley's original model (1986) included a central executive, phonological loop and visuospatial sketchpad and was deemed separate from long-term memory (LTM). While this simple model explained a range of data (e.g., phonological similarity, word-length effect), it could not account for all experimental phenomena. For example, the visuospatial sketchpad, a capacity limit of 4 units was observed for the maintenance of individual features (colors or orientations) as well as for integrated
Empirical evidence from subclinical checkers
With these points in mind, our recent experiments (Harkin and Kessler, 2009, Harkin and Kessler, 2011, Harkin et al., 2011) set out to: (1) engage the EB using stimuli that required multimodal conjunctions between various object features and spatial locations and to (2) hamper EB functionality by confronting high and low checkers with misleading/irresolvable information during the WM retention interval. In Harkin and Kessler (2009), we employed this novel paradigm for the first time. We
The EBL (Executive-Functioning, Binding Complexity, Memory Load) classification system
Our synthesis so far leads us to conclude that checkers' memory impairment results from a complex interaction between (1) executive dysfunction in encoding organization, multimodal integration, selective attention (inhibition), maintenance control, and set-shifting and (2) the task components of load (e.g., high load, requiring chunking), multimodality (e.g., location + identity + color), distraction (e.g., dual task paradigm), retrieval dimension (e.g., location), and stimulus salience (e.g.
Applying the EBL classification system to 58 experimental findings
Fig. 1 explains where we do and do not expect to observe OCD memory impairments relative to controls; this we suggest is influenced by the degree of executive function efficiency (E), binding complexity (B) and memory load (L) within any given neuropsychological task. First, we do not expect memory performance to differ between OCD patients and controls for tasks that are low in executive demand, binding and load (see: white region in top-left quadrant of Fig. 1). Second, likelihood for
Comparison of EBL classification system to other models in the OCD literature
The EBL classification system allowed us to explain, in a unified manner, how executive impairments observed in OCD/checking tend to impair memory when the episodic buffer is extensively relied upon. However, we are aware that our EBL classification system is primarily cognitive in nature, which poses the question: How does it relate to alternative and more phenomenogical explanations of OCD symptoms in general and of memory impairments in particular?
Salkovskis (1999) provided one of the most
Limitations of the EBL classification system
We highlight the following limitations to the EBL classification system. First, it is a good fit for OCD patients with prominent checking cognitions/behaviors, but appears not to describe symptoms such as cleaning or hoarding. We propose that if the EBL factors are sufficiently stressed (as discussed above) then memory impairment could be observed in symptoms other than checking. However, we do concur that due to the specific impairments (i.e., inhibition; Omori et al., 2007) and cognitive
Conclusions
This review reconciles inconsistent findings as to memory deficits in OCD by suggesting that the classic view in terms of modality-specific (verbal vs. visuospatial) deficits and/or general capacity issues might not be the optimal way of conceiving of the problem, while we propose to follow and extend the more recent argument that OCD memory impairments are secondary to executive dysfunction. Using our research as a basis, we argue that memory impairments occur when: (1) a task taps into
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