Checking-in on the memory deficit and meta-memory deficit theories of compulsive checking

Clinical Psychology Review 29 (2009) 393–409

Contents lists available at ScienceDirect

Clinical Psychology Review

Checking-in on the memory deficit and meta-memory deficit theories ofcompulsive checking

Carrie Cuttler ⁎, Peter GrafDepartment of Psychology, University of British Columbia, 2136 West Mall, Vancouver, BC, Canada V6T 1Z4

⁎ Corresponding author. Tel.: +1 604 822 6265; fax:E-mail addresses: [email protected] (C. Cuttler),

0272-7358/$ – see front matter © 2009 Elsevier Ltd. Adoi:10.1016/j.cpr.2009.04.003

a b s t r a c t
a r t i c l e i n f o
Article history:Received 22 July 2008Received in revised form 19 March 2009Accepted 2 April 2009

Keywords:Obsessive–compulsive disorderChecking compulsionsMemory deficit theoryMeta-memoryConfidenceProspective memory

The memory deficit theory and meta-memory deficit theory provide intuitive accounts for checkingcompulsions. According to these theories, deficits in memory and/or a lack of confidence in memorycontribute to the compulsion to check. Our goal was to examine whether, as predicted by the theories,memory deficits and/or meta-memory deficits are unique to individuals with checking compulsions asopposed to being common to all OCD patients. The review revealed that previous investigations of thesetheories have focused almost exclusively on retrospective memory. More importantly, results of the reviewrevealed similar patterns of deficits in the retrospective memory performance and meta-memory scores ofOCD checkers and OCD non-checkers, indicating that deficits in retrospective memory are not unique tocheckers and therefore are unlikely to contribute to the compulsion to check. The review also features resultsof the few studies that have examined the theories in the context of prospective memory, and it provides theresults of some supplementary analyses which show that checkers demonstrate unique memory and meta-memory deficits related to prospective memory. Together these results indicate that the memory deficit andmeta-memory deficit theories should be re-conceptualized and further examined in the context ofprospective memory.

© 2009 Elsevier Ltd. All rights reserved.

Contents

1. General method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3951.1. Scope of reviews . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3951.2. Expectations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3951.3. Organization of result tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395

2. Memory deficits and meta-memory deficits in . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3962.1. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396

2.1.1. Memory for actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3962.1.2. Memory for source information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3972.1.3. Memory for visual and/or spatial materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3982.1.4. Memory for verbal materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 400

2.2. Summary and discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4003. Memory deficits and meta-memory deficits in . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404

3.1. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4043.1.1. Supplementary analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404

3.2. Summary and discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4054. General discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407

+1 604 822 [email protected] (P. Graf).

ll rights reserved.

Obsessive–Compulsive Disorder (OCD) is an anxiety disorder thatafflicts approximately 3% of the population (Kolada, Bland, & Newman,1994; Stein, Forde, Anderson, & Walker, 1997). The disorder is charac-terized by obsessions and compulsions. Obsessions are intrusive and

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394 C. Cuttler, P. Graf / Clinical Psychology Review 29 (2009) 393–409

persistent thoughts, images, or impulses that are unwanted andcause anxiety (Rachman & Shafran, 1998). Compulsions are repeti-tive behaviors or mental acts such as washing, counting, or checkingwhich are typically initiated to reduce the anxiety generated byobsessions (Rachman & Shafran, 1998; Tallis, 1995a).

OCD is a heterogeneous disorder with many different subtypeswhich have been delimited by means of both observation andempirical investigations (Fontenelle, Mendlowicz, & Versiani, 2005;Hasler et al., 2005; Henderson & Pollard, 1988; Mataix-Colis,Rosario-Campos, & Leckman, 2005; McKay et al., 2004). The mostcommon subtype, characterized by checking compulsions, occurs inover 50% of OCD patients (Henderson & Pollard, 1988; Rasmussen &Eisen, 1988; Stein et al., 1997), with an additional 15% of the generalpopulation demonstrating sub-clinical checking compulsions (Steinet al., 1997). Individuals with checking compulsions have intrusivedoubts that they failed to perform a task and/or failed to perform itproperly. They worry that if they made an error, some harm willbefall themselves or someone else, and then they feel compelled tocheck to ensure that the task was indeed performed correctly(Müller & Roberts, 2005; Rachman & Shafran, 1998; Woods, Vevea,Chambless, & Bayan, 2002). Concretely, an individual with checkingcompulsions may have a recurring intrusive doubt that s/he forgotto unplug the iron, worry about the consequences of such a failure(e.g., starting a fire) and then feel compelled to return home tocheck on the status of the iron at the expense of attending to otheractivities.

Causes of OCD are still unclear. Biological accounts point toevidence that OCD tends to run in families, that it is associated withfronto-striatal abnormalities as well as with increased serotonergicresponsiveness (Tallis, 1995a). Behavioral accounts of OCD focus onpatients' dysfunctional beliefs and attitudes (e.g., an exaggeratedsense of responsibility), as well as on memory deficits, attentionalbiases and problems with inhibition (Müller & Roberts, 2005; Tallis,1995a). In line with these accounts, the most common treatments forOCD are pharmacological and behavioral. Pharmacological interven-tions involve serotonin transport inhibitors (Greist, Jefferson, Kobak,Katzelnick, & Serlin, 1995; Pigott & Seay, 1998), and the most commonbehavioral intervention, cognitive behavior therapy, tends to focus onexposure and response prevention (Foa, Franklin, & Kozak, 1998;Rowa, Antony, & Swinson, 2007).

In this article we focus on a behavioral account of checkingcompulsions which has important implications for treatment.Although foreshadowed in the writings of Janet (1903) and Freud(1909), Sher, Frost, and Otto (1983) were the first to articulate andempirically examine its basic assumptions. Sher et al. suggested, first,that “compulsive checkers may simply be poorer at memory for prioractions, necessitating repeated checks” (pg. 358), second, that thecompulsion to check may be driven by the failure to distinguishbetween memory for actual versus imagined events (e.g., havingunplugged the iron versus thinking about unplugging it), and third,that the compulsion to check may arise from a lack of confidence inthis ability. Since Sher et al.'s seminal contribution investigators havemade a distinction between a memory deficit theory – the claim thatcheckers have a memory deficit which contributes to the compulsionto check, and a meta-memory deficit theory – the claim that it ischeckers' diminished confidence in their memory abilities whichcontributes to the compulsion to check.

What evidence is available to support these theoretical claims? Ourprimary objective was to find out whether there is compellingevidence that memory deficits and/or meta-memory deficits areunique to individuals with checking compulsions. The focus on deficitsunique to checkers was brought to the fore by Tallis, Pratt, and Jamani(1999)who observed that “unlike checking, there is no obvious reasonwhy…memory problems should be of aetiological significance withrespect to other obsessional symptoms” (p.165). Radomsky, Rachman,and Hammond (2001) made the same point by noting that “Patients

rarely say that they are washing their hands again and again becausethey don't recall washing them earlier, but they do report an inabilityto remember if a check, say of the stove, was completed correctly” (p.815). Consistent with such observations and the theoretical claims bySher et al. (1983), it follows that if memory and/or meta-memorydeficits contribute to the compulsion to check then the evidenceshould show that these deficits are unique to individuals withchecking compulsions. If all individuals with OCD were to exhibitsimilar deficits in memory or meta-memory, this finding wouldsuggest that the deficits are a consequence of some factor associatedwith OCD (e.g., anxiety, depression, medication, brain abnormalities)rather than linked with the compulsion to check. At the very least, ifmemory or meta-memory deficits contribute to the compulsion tocheck then the evidence should show that such deficits aresignificantly more severe in checkers than in other individuals withOCD.

Our primary objective is relevant to a number of previous reviews.Among them are reviews on the neuropsychological status ofindividuals with OCD (Cox, 1997; Müller & Roberts, 2005; Otto,1992; Savage, 1998; Tallis, 1995a,b, 1997), and especially prominent, arelatively recent meta-analytic review by Woods et al. (2002) whichfocused specifically on the memory deficit and meta-memory deficittheories of checking compulsions. In combination, these reviewsprovide fairly compelling evidence that memory and other cognitivefunctions are impaired in OCD patients and in checkers. By contrast toour objective, however, previous reviews were not specificallydesigned to investigate whether memory deficits are unique tocheckers. That is, the previous reviews asked about the presenceversus absence of memory deficits in OCD patients and checkers, butthey did not compare and contrast, for example, the memoryperformance of OCD checkers with that of OCD non-checkers. Weundertook the direct comparison of these subgroups of OCD patientsin order to examine the critical claim that a deficit in memory and/ormeta-memory contributes to the compulsion to check.

Our second objective was to examine the memory deficit andmeta-memory deficit theories in the domain of prospective memory,which is the ability to formulate intentions, plans, and promises, andto retain, recollect, and carry them out at the appropriate time or inthe appropriate context (Einstein & McDaniel, 1996; Graf, 2005;Meacham & Dumitru, 1976). Nearly every prior investigation of thememory deficit theory and meta-memory deficit theory has focusedon retrospective memory, which is broadly defined as the ability toremember previously learned information, facts, or events, while onlya few studies have examined these theories in the context ofprospective memory.

It is somewhat surprising that previous investigators have notfocused more on the ability to remember to perform intendedactions because everyday-life and clinical observations show thatcheckers' compulsions are related to this future-oriented aspect ofmemory. Checkers tend to be concerned with whether or not theiron or stove is turned off and whether doors or windows are pro-perly shut and locked, that is with tasks whose proper executiondepends on prospective memory. Moreover, deficits in thisdomain may provide an intuitive account of the origins of the intru-sive doubts that instigate checking. If checkers have a deficit inprospective memory and they frequently experience prospectivememory failures, they may begin to worry about and developintrusive doubts concerning these failures. When the perceivedconsequences of a prospective memory failure are serious (e.g., thefailure to unplug the iron after use might cause a fire), these intrusivedoubts may lead to checking behavior.

In the first section of this paper we examine the memory deficitand meta-memory deficit theories in the domain of retrospectivememory. We review the large body of literature that has focused onretrospective memory deficits in checkers and OCD patients moregenerally in order to determine whether retrospective memory

395C. Cuttler, P. Graf / Clinical Psychology Review 29 (2009) 393–409

deficits are unique to checkers as opposed to being common to allOCD patients. In the second section, we examine the memorydeficit and meta-memory deficit theories in the domain of pros-pective memory. We review the few studies that have examinedprospective memory in checkers and OCD patients more generallyand also provide some supplementary analyses in an attempt togain insights into whether prospective memory deficits are uniqueto checkers.

1. General method

1.1. Scope of reviews

To locate publications of relevance to our goals, we used each of thebasic terms “memory,” “confidence,” and “meta-memory” in combi-nation with each of the following – “obsessive compulsive disorder,”“obsessive–compulsive disorder,” “OCD,” “check,” and “checking” – tosearch PsycINFO and Google Scholar. Next, we did a follow up searchof the reference section of each document which was produced by theinitial search. From results of these searches, we excluded alldocuments which did not report original empirical research. For theremaining documents, we reviewed the abstract and if necessary themethod section in order to identify studies that focused on explicitepisodic memory (Graf & Schacter, 1985), episodic prospectivememory or habitual prospective memory (Graf & Uttl, 2001; Uttl,2008). We excluded investigations on other aspects of memory (e.g.,semantic memory, implicit memory, working memory, directedforgetting, memory biases) because although they are important forunderstanding OCD, these aspects of memory are not directlyimplicated by either the memory deficit theory or the meta-memorydeficit theory of compulsive checking.

Our search and selection process yielded a total of 67 empiricalarticles. Sixty-four of these articles focused on retrospective memory,two focused on prospective memory and one focused on bothdomains of memory. Twenty-one of these articles included compar-isons between various kinds of checkers (OCD and sub-clinical) andhealthy controls, 50 included comparisons between OCD patients andhealthy controls, 13 included comparisons between OCD patients andpsychiatric controls and 15 articles compared OCD patients withchecking compulsions and OCD patients without checking compul-sions. In total, the articles present data from over 1580 healthy controlparticipants, 258 psychiatric control participants, over 236 sub-clinical checkers and 1519 OCD patients. Of the latter group, 385were described as OCD checkers, 219 were described as OCD non-checkers and the remaining 915 were not described in detail.

1.2. Expectations

Evidence relevant to the memory deficit and meta-memory deficittheories comes from investigations with a variety of populations,especially the following: OCD patients (i.e. individuals with an Axis Idiagnoses of OCD who are not screened for specific symptoms), OCDcheckers (i.e. individuals with an Axis I diagnosis of OCD whofrequently experience the compulsion to check), and sub-clinicalcheckers (i.e. individuals – typically community living adults includ-ing undergraduate students – who do not have an Axis I diagnosis ofOCD although they frequently experience the compulsion to check). Inprevious investigations, these populations have been compared toOCD non-checkers (i.e., individuals with an Axis I diagnosis of OCDwho do not experience checking compulsions), to psychiatric controls,to healthy controls, and to non-checkers. The latter two groups differonly by virtue of the fact that the non-checkers have been specificallyscreened for the absence of checking compulsions.

Availability and accessibility of these different groups of partici-pants is likely to be one, probably the most important, reason fortheir differential use in previous investigations. However, the theo-

retical claim that memory deficits and meta-memory deficitscontribute to the compulsion to check is addressed most directlyand relevantly by investigations which have compared OCDcheckers to OCD non-checkers. These two patient groups are likelyto be characterized by similar comorbid disorders (e.g., anxiety,depression), and to suffer from the same potentially negative con-sequences of medication and brain dysfunction. Consistent withthe memory deficit theory and the meta-memory deficit theory,we expected the extant research either to reveal memory deficitsand meta-memory deficits only in the OCD checkers, or to revealsignificantly larger deficits in the OCD checkers than in the OCD non-checkers.

Only a relatively small number of investigations have directlycompared OCD checkers and OCD non-checkers. However, additionalpertinent evidence is available from a number of investigations thathave compared the memory test performance and meta-memoryscores of sub-clinical checkers and non-checkers. Sub-clinicalcheckers are typically free of the medications that may confoundthe memory performance and meta-memory scores of OCD check-ers; moreover, they have fewer and less severe forms of the comorbiddisorders which are known to afflict OCD patients (Gibbs, 1996). Inaddition, sub-clinical checking compulsions are muchmore common(prevalence in the general population is estimated to be about 15%)than OCD checking compulsions (Sher et al., 1983; Stein et al., 1997),and thus, studies with sub-clinical checkers have tended to involvelarger subject groups. Finally, and most importantly, it is generallyagreed that sub-clinical and clinical checking compulsions are notfundamentally different, that checking compulsions occur on acontinuum which maps the frequency of experiencing the compul-sion to check, the degree to which the compulsions interfere withdaily functioning and the level of distress that is caused by them(Gibbs, 1996; Rasmussen & Eisen, 2002). Consistent with thischaracterization of sub-clinical checkers we expected the extantresearch to show memory deficits and meta-memory deficits in thesub-clinical checkers.

1.3. Organization of result tables

To summarize the findings, we have created five tables, four ofwhich pertain to retrospective memory and one (included in the nextsection of this report) that pertains to prospective memory. Each ofthe first four tables is dedicated to a content defined area ofretrospective memory, specifically to memory for actions (Table 1),to memory for source information (Table 2), to memory for visual/spatial materials (Table 3), and to memory for verbal materials(Table 4). We arranged these tables in this manner at least in partbecause of theoretical considerations, because of the claim by Sheret al. (1983) that compulsive checking may be triggered either bydifficulties with remembering prior actions (e.g., turning off thestove), or by the failure to distinguish between memory for actualversus imagined events (e.g., did I turn off the stove or only thinkabout it?). Consistent with the first of these suppositions, weanticipated discovering unique checking-related deficits either onlyin investigations concerned with action memory or larger deficitsin these investigations than in those focusing on memory for visualor verbal materials. Consistent with the second supposition, weanticipated discovering unique checking-related deficits in studiesconcerned with source memory. Clinical observations illustratethat checkers tend to be concerned with tasks that requireprospective memory, and thus, we also anticipated discoveringunique checking-related deficits in this domain of memory (i.e. in theresults summarized in Table 5).

A comparison of Tables 1–4 shows that action and sourcememory have been investigated far less frequently than eitherverbal memory or visual memory, even though only the former twohave been specifically linked to the memory and meta-memory


deficit theories of checking compulsions. However, the preponder-ance of research related to verbal and visual memory should notbe interpreted as an overgeneralization of these theories; rather it isa consequence of the fact that most of the available data have comefrom investigations of the neuropsychology of OCD rather thanfrom studies specifically focused on the memory and meta-memorydeficit theories.

Each table is arranged into four main sections. The 1st sectionsummarizes results from studies that involved a direct comparisonbetween OCD checkers and OCD non-checkers. As argued earlierin this report, research with these specific populations speaks mostdirectly to the memory deficit theory and the meta-memory deficittheory. Despite their relevance, however, Tables 1–5 show thatonly a relatively small number of studies of this type are currentlyavailable.

The 2nd section of each table summarizes results from studies thatcompared sub-clinical checkers with non-checkers, that is, healthycontrols who have been screened for checking compulsions. Con-sistent with the assumption that OCD checkers and sub-clinicalcheckers are not fundamentally different from each other, that theymerely represent different points on the same continuum (Gibbs,1996; Rasmussen & Eisen, 2002), it may be argued that comparisonsbetween these groups are also directly relevant to the memory deficittheory and to the meta-memory deficit theory. We accept thisargument but with reservations because of the evidence that sub-clinical checking is accompanied by many of the same afflictionsknown to occur in clinical checking (e.g., anxiety, depression) (Cuttler& Graf, 2008; Frost, Sher, & Geen,1986; Gibbs, 1996; Morris, Blashfield,Rankupalli, Bradley, & Goodman, 1996). As a consequence, thecomorbid afflictions known to be present in sub-clinical checkersare a potentially serious confound in any comparison between sub-clinical checkers and non-checkers.

Studies which have compared OCD checkers with healthy controls,listed in the 3rd section of each table, may be viewed as similar tothose in the 2nd section, except that potential confounds are evenmore likely and thus more serious. OCD checkers and sub-clinicalcheckers differ in potentially important ways, including in theirdegree of comorbid anxiety and depression, their history of (years ofsuffering from) checking compulsions, and their use of medication ortherapy for treating compulsive behaviors. All such potentialconfounds must be identified and their influence on cognition needsto be removed if memory differences from studies with OCD checkersand healthy controls are to be used in support of the memory deficitand meta-memory deficit theories of compulsive checking.

In the 4th section of each table we list studies that focused onthe neuropsychology of OCD rather than being specifically con-cerned with the memory deficit or meta-memory deficit theories ofcompulsive checking. Comparisons between OCD patients andhealthy controls are not directly relevant to the theories becausethe memory deficit theory and the meta-memory deficit theorymake claims which are specific to checkers. Nevertheless, studiescomparing OCD patients with healthy controls are useful forevaluating the claims that memory and meta-memory deficits areunique to checkers. On the assumption that these deficits are uniqueto checkers, we expected either to find deficits only in the studiessummarized in the 3rd but not in the 4th section of our tables or atleast to find larger deficits in the 3rd than 4th section. By con-trast, similar deficits in the studies listed in the 3rd and 4th sectionswould indicate that memory deficits are a common feature of OCD(perhaps caused by anxiety, depression, medication, or braindysfunction) and thus without etiological significance for checkingcompulsions.

In the final section of each table we list studies that have comparedOCD patients with psychiatric controls. Once again, rather than beingspecifically concerned with the memory deficit and meta-memorydeficit theories of compulsive checking these studies focused on the

neuropsychology of OCD. Authors of these studies recognized themany confounds which obscure direct comparisons of OCD patientsand healthy controls and included a psychiatric control group in anattempt to control for these confounds. We provide a summary ofthese studies for a similar reason, to gauge the potential influence ofconfounds that afflict comparisons of OCD patients or OCD checkerswith healthy controls.

Each table has six columns showing: authors of each study, thetype of test or instrument used for the study, the subject target andcomparison groups, the findings relevant to the memory deficittheory, and finally the findings relevant to the meta-memory deficittheory. Many authors appear more than once in the first columnbecause many investigations have employed more than one assess-ment instrument and have focused and reported on more than onepotential between group difference. The 2nd column of each tableidentifies the instruments or methods used to assess memory ormeta-memory. All standardized, commercially available instrumentsare identified by their common names, and we have used the labelproprietary to mark studies which used an in-house (i.e., non-standardized) method.

Results of our review are listed in the last two columns of eachtable. Because of the small number of studies in the most critical topsection of each table (i.e., studies comparing OCD checkers with OCDnon-checkers), and because a large proportion of studies do notprovide information on variability, it was not possible to calculateeffect sizes and apply conventional meta-analytic techniques to eachof our data sets. For this reason, we opted for a simple count ofrelevant significant differences that were reported.

In many cases, the assessment instrument or method which wasemployed yielded a number of different sub-scores, and the authorsreported the presence or absence of significant between groupdifferences in these sub-scores. To accommodate this situation, thetables show the number of significant differences which favored thememory deficit theory or the meta-memory deficit theory, over thetotal number of significance tests. For the purpose of computing thisratio, we classified as a failure each of the few significant findingswhich went against the outcome expected by the memory deficittheory or the meta-memory deficit theory.

Our analysis does not include studies for which the results showedceiling or floor effects. Specifically, we did not count any statistical testoutcomes that involved a mean which was within one standarddeviation of the maximum or minimum possible score. Only a smallnumber of ceiling and floor effects were discovered (b1%) and mostwere associated with recognition tests. We chose not to include theseresults because in such cases the failure to find group differences mayreflect a lack of sensitivity.

2. Memory deficits and meta-memory deficits inretrospective memory

2.1. Results

2.1.1. Memory for actionsSher et al. (1983) proposed over two decades ago that compulsive

checking may be triggered by difficulties with remembering intendedactions (e.g., locking the door, turning off the iron), and yet, only arelatively small number of studies have examined OCD checkers' andOCD patients' ability to remember actions (see Table 1). In most ofthese studies, memory for actions was assessed by means of aproprietary test. To illustrate, Sher et al. (1983), Sher, Mann, and Frost(1984), and Sher, Frost, Kusner, Crews, and Alexander (1989) assessedaction memory by requiring participants to recall at the end of theexperiment all of the different tasks they completed in the course ofthe experiment. In other studies where the focus was primarily onsource memory, participants were presented with brief task descrip-tions (e.g., break the match, bend the paperclip) which had to be

Table 1A summary of the results of research on action memory.

Test OCD group Comparison group Memorydeficit

Meta-memorydeficit

1. OCD checkers and OCD non-checkersCougle, Salkovskis, and Wahl (2007) Memory for Actions and Events Questionnaire OCD checkers (n=39) OCD non-checkers (n=20) n/a 4/8Hermans, Martens, De Cort, Pieters,and Eelen (2003)

Meta-Cognitions Questionnaire OCD checkers (n=9) OCD non-checkers (n=8) n/a 0/1

Jelinek et al. (2006) Rivermead Behavioural Memory — Route OCD checkers (n=23) OCD non-checkers (n=8) 0/2 n/aMcNally and Kohlbeck (1993) Proprietary OCD checkers (n=12) OCD non-checkers (n=12) 0/2 0/1

Overall 0/4 4/10

2. Sub-clinical checkers and non-checkersRoth and Baribeau (1996) Self-Ordered Pointing Sub-clinical checkers (n=14) Non-checkers (n=14) 1/2 n/aEcker and Engelkamp (1995) Proprietary Sub-clinical checkers (n=24) Non-checkers (n=48) 0/9 n/aRubenstein, Peynircioglu, Chambless,and Pigott (1993) Exp 1a

Proprietary Sub-clinical checkers (n=20) Non-checkers (n=20) 2/2 n/a

Rubenstein et al. (1993) Exp 1b Proprietary Sub-clinical checkers (n=19) Non-checkers (n=20) 0/2 n/aSher et al. (1983) Proprietary Sub-clinical checkers (n=26) Non-checkers (n=28) 1/1 n/aSher et al. (1984) Proprietary Sub-clinical checkers (n = a) Non-checkers (n = a) 0/1 n/aSher et al. (1989) Proprietary Sub-clinical checkers (n=13) Non-checkers (n=12) 1/2 n/aZermatten, Van der Linden, Larøi,and Ceschi (2006)

Proprietary Sub-clinical checkers (n=19) Non-checkers (n=35) 1/7 1/20

Overall 6/26 1/20

3. OCD checkers and healthy controlsCougle et al. (2007) Memory for Actions and Events Questionnaire OCD checkers (n=39) Healthy controls (n=69) n/a 4/8Hermans et al. (2008) Brief Cognitive Confidence Questionnaire OCD checkers (n=16) Healthy controls (n=16) n/a 2/2Constans, Foa, Frankin, andMathews (1995)

Proprietary OCD checkers (n=12) Non-checkers (n=7) 0/2 n/a

Ecker and Engelkamp (1995) Proprietary OCD checkers (n=24) Non-checkers (n=48) 1/9 n/aMcNally and Kohlbeck (1993) Proprietary OCD checkers (n=12) Non-checkers (n=12) 0/2 0/1

Overall 1/13 6/11

4. OCD patients and healthy controlsCougle et al. (2007) Memory for Actions and Events Questionnaire OCD non-checkers (n=20) Healthy controls (n=69) n/a 1/8Galderisi, Mucci, Catapano, D'Amato,and Maj (1995)

Self-Ordered Pointing OCD patients (n=22) Healthy controls (n=21) 0/2 n/a

Hermans et al. (2003) Meta-Cognitions Questionnaire OCD patients (n=17) Non-checkers (n=17) n/a 1/1Jelinek et al. (2006) Rivermead Behavioural Memory — Route OCD patients (n=31) Healthy controls (n=33) 0/2 n/aMartin, Wiggs, Altemus, Rubenstein,and Murphy (1995)

Self-Ordered Pointing OCD patients (n=18) Healthy controls (n=18) 0/18 n/a

McNally and Kohlbeck (1993) Proprietary OCD non-checkers (n=12) Non-checkers (n=12) 1/2 0/1Overall 1/24 2/10

5. OCD patients and psychiatric controlsCougle et al. (2007) Memory for Actions and Events Questionnaire OCD non-checkers (n=20) Psychiatric controls (n=22) n/a 0/4Hermans et al. (2008) Brief Cognitive Confidence Questionnaire OCD patients (n=16) Psychiatric controls (n=16) n/a 2/2

Overall n/a 2/6

a Data are unavailable.


carried out, written on paper, imagined, or simply observed (i.e.,observe the action being performed by the experimenter). For theactionmemory test, participantswere required to record all of the taskdescriptions and/or all of the tasks which they had performed.

As shown on the top portion of Table 1, we found four statisticalcomparisons concerning the action memory test scores of OCDcheckers and OCD non-checkers and none of these was significant.In contrast, we found 10 statistical comparisons between OCDcheckers' and OCD non-checkers' action related meta-memory scoresand four of these revealed greater deficits in the OCD checkers.

The 2nd portion of Table 1 lists 26 comparisons concerning theaction memory test performance of sub-clinical checkers and non-checkers, with six showing a significant deficit in the sub-clinicalcheckers. Our review revealed only one study which focused on theaction related meta-memory of sub-clinical checkers and non-checkers; despite making 20 statistical comparisons, only onerevealed a greater meta-memory deficit in the sub-clinical checkers.

The 3rd section of Table 1 shows 13 statistical comparisons on theaction memory test performance of OCD checkers and healthy controls.Only one of these comparisons revealed a deficit in the OCD checkers.The table also shows 11 comparisons of these groups' action meta-memory, six of which showed a deficit in the OCD checkers.

The 4th section of Table 1 lists 24 comparisons on the actionmemory test performance of OCD patients and healthy controls andonly one of these comparisons showed a significant deficit in the OCDpatients. In addition, there were 10 comparisons of OCD patients' andhealthy controls' meta-memory, with two of them revealing a deficitin OCD patients.

As shown in the bottom section of Table 1 our search of theliterature did not reveal any studies that have compared OCD patients'action memory test performance with psychiatric controls. However,we did locate studies that compared these two groups' action meta-memory. As shown in the table, of the six comparisons of OCDpatients' and psychiatric controls' action meta-memory, two revealeda greater meta-memory deficit in OCD patients.

2.1.2. Memory for source informationMemory for source information, hereinafter source memory (an

ability which is often called realitymonitoring), concerns the ability toremember the source from which information has been obtained(Johnson, Hashtroundi, & Lindsay, 1993). Source memory is importantfor deciding, for example, whether news of a friend's engagement wasobtained first-hand from the friend or second-hand from anacquaintance of the friend. This type of memory is relevant to

Table 2A summary of the results of research on source memory.

Test OCD group Comparison group Memory deficit Meta-memory deficit

1. OCD checkers and OCD non-checkersHermans et al. (2003) Meta-Cognitions Questionnaire OCD checkers (n=9) OCD non-checkers (n=8) n/a 0/1Brown, Kosslyn, Breiter, Baer,and Jenike (1994)

Proprietary OCD checkers (n=13) OCD non-checkers (n=9) 0/2 n/a

Hermans et al. (2003) Proprietary OCD checkers (n=9) OCD non-checkers (n=8) 0/9 0/2McNally and Kohlbeck (1993) Proprietary OCD checkers (n=12) OCD non-checkers (n=12) 0/7 0/6Merckelbach and Wessel (2000) Proprietary OCD checkers (n=7) OCD non-checkers (n=12) 0/1 0/1Moritz, Jacobsen, Willenborg,Jelinek, and Fricke (2006)


Overall 0/64 0/10

2. Sub-clinical checkers and non-checkersEcker and Engelkamp (1995) Proprietary Sub-clinical checkers (n=24) Non-checkers (n=48) 1/8 3/4Rubenstein et al. (1993) Exp 1a Proprietary Sub-clinical checkers (n=20) Non-checkers (n=20) 1/1 n/aRubenstein et al. (1993) Exp 3 Proprietary Sub-clinical checkers (n=19) Non-checkers (n=20) 1/2 n/aSher et al. (1983) Proprietary Sub-clinical checkers (n=26) Non-checkers (n=28) 0/2 1/1Zermatten et al. (2006) Proprietary Sub-clinical checkers (n=19) Non-checkers (n=35) 2/13 n/a

Overall 5/26 4/5

3. OCD checkers and healthy controlsHermans et al. (2008) Meta-Cognitions Questionnaire OCD checkers (n=16) Healthy controls (n=16) n/a 1/1Brown et al. (1994) Proprietary OCD checkers (n=13) Healthy controls (n=18) 0/2 n/aConstans et al. (1995) Proprietary OCD checkers (n=12) Non-checkers (n=7) 0/2 0/2Ecker and Engelkamp (1995) Proprietary OCD checkers (n=24) Non-checkers (n=48) 1/8 4/4McNally and Kohlbeck (1993) Proprietary OCD checkers (n=12) Non-checkers (n=12) 0/7 1/6Moritz, Jacobsen et al. (2006) Proprietary OCD checkers (n=17) Healthy controls (n=51) 0/45 0/11

Overall 1/64 6/24

4. OCD patients and healthy controlsHermans et al. (2003) Meta-Cognitions Questionnaire OCD patients (n=17) Non-checkers (n=17) n/a 1/1Brown et al. (1994) Proprietary OCD patients (n=26) Healthy controls (n=18) 0/2 n/aHermans et al. (2003) Proprietary OCD patients (n=8) Non-checkers (n=17) 0/9 0/3McNally and Kohlbeck (1993) Proprietary OCD non-checkers (n=12) Non-checkers (n=12) 0/7 3/6Merckelbach and Wessel (2000) Proprietary OCD patients (n=19) Healthy controls (n=16) 0/1 1/1Moritz, Jacobsen et al. (2006) Proprietary OCD patients (n=27) Healthy controls (n=51) 3/45 0/11

Overall 3/64 5/22

5. OCD patients and psychiatric controlsHermans et al. (2008) Meta-Cognitions Questionnaire OCD patients (n=16) Psychiatric controls (n=16) n/a 1/1

Overall n/a 1/1


checking compulsions, in part, because it is required for distinguishingbetween imagined (internal) and real (external) events, for example,between thinking about turning off the iron and actually doing it.

To our knowledge, there exist no standardized methods orinstruments for assessing source memory, and thus, a wide varietyof different methods have been used in the studies listed in Table 2. InPhase 1 of a typical experiment on source memory, participants maybe presented with a series of simple action statements, some to beperformed by the participants, others to be performed by theexperimenter or to be imagined or simply to be written down. Aftera delay, the action statements are re-presented and the participants'task is to recollect how the action statements were experienced.

As shown in the top portion of Table 2, we discovered 64 statisticalcomparisons concerning the source memory test performance of OCDcheckers and OCD non-checkers, none of which revealed a deficit inthe OCD checkers. In addition, there have been 10 comparisons of OCDcheckers' and OCD non-checkers' source meta-memory, none ofwhich revealed a deficit.

The next segment of Table 2 lists 26 statistical comparisons of thesource memory test performance of sub-clinical checkers and non-checkers and five of those showed a significant deficit in the sub-clinical checkers' scores. Of the five statistical comparisons of sub-clinical checkers' and non-checkers' source meta-memory, fourshowed a deficit in the sub-clinical checkers.

The 3rd section of Table 2 lists 64 comparisons of OCD checkers'and healthy controls' source memory test performance and only oneshowed a deficit in the OCD checkers. There were 24 comparisons

involving meta-memory scores, and six of these showed a significantdeficit in the OCD checkers.

The 4th portion of Table 2 shows that there have been 64comparisons of the source memory test performance of OCD patientsand healthy controls, three of which were significant. The table alsolists 22 comparisons related to the meta-memory scores of the samegroups, with five showing a significant deficit in the OCD patients.

As shown in the bottom section of Table 2 our literature search didnot reveal any studies that have compared the source memory testperformance of OCD patients and psychiatric controls. However, wedid locate one study that compared these two groups' source meta-memory. The study involved one statistical comparisonwhich showeda greater deficit in the source meta-memory of OCD patients.

2.1.3. Memory for visual and/or spatial materialsTable 3 highlights the wealth of research on checkers' and OCD

patients' memory for visual (i.e., non-verbal) and/or spatial materials.This fortunate situation is due to the fact that these aspects of memoryare at the core of every neuropsychological test battery, and becausealmost every study with psychiatric patients involves at least one suchbattery. Because of the direct link to neuropsychological assessments,most of the data on visual and/or spatial memory have been collectedby means of standardized methods, as opposed to the proprietarymethods which were used for the studies listed in Tables 1 and 2.

As shown in the top portion of Table 3 we located eightcomparisons concerning the visual/spatial memory test performanceof OCD checkers and OCD non-checkers, two of which revealed a

Table 3A summary of the results of research on visual memory.


1. OCD checkers and OCD non-checkersCha et al. (2008) Rey Complex Figures OCD checkers (n=24) OCD non-checkers (n=23) 2/2 n/aMoritz, Kloss, Jahn, Schick,and Hand (2003)

Rey Complex Figures OCD checkers (n=23) OCD non-checkers (n=9) 0/2 n/a

Moritz et al. (2003) Corsi Block Tapping OCD checkers (n=23) OCD non-checkers (n=9) 0/1 n/aOmori et al. (2007) WMS-Visual OCD checkers (n=27) OCD non-checkers (n=26) 0/1 n/aJelinek et al. (2006) RBMT — Pictures and Faces OCD checkers (n=23) OCD non-checkers (n=8) 0/2 n/aTolin et al. (2001) Proprietary OCD checkers (n=5) OCD non-checkers (n=9) n/a 1/18

Overall 2/8 1/18

2. Sub-clinical checkers and non-checkersRoth and Baribeau (1996) WMS-Visual Reproduction Sub-clinical checkers (n=14) Non-checkers (n=14) 0/2 n/aSher et al. (1984) WMS-Visual Reproduction Sub-clinical checkers (n = a) Non-checkers (n = a) 0/1 n/aSher et al. (1989) WMS-Visual Reproduction Sub-clinical checkers (n=13) Non-checkers (n=12) 1/1 n/a

Overall 1/4 n/a

3. OCD checkers and healthy controlsCha et al. (2008) Rey Complex Figures OCD checkers (n=24) Healthy controls (n=20) 2/2 n/aTallis et al. (1999) Corsi Block Tapping OCD checkers (n=12) Healthy controls (n=12) 0/1 n/aZitterl et al. (2001) Corsi Block Tapping OCD checkers (n=27) Healthy controls (n=27) 1/1 n/aTallis et al. (1999) Recurring Figures OCD checkers (n=12) Healthy controls (n=12) 2/2 n/aTallis et al. (1999) Figure Recall OCD checkers (n=12) Healthy controls (n=12) 2/2 n/aZitterl et al. (2001) LGT-3 OCD checkers (n=27) Healthy controls (n=27) 1/1 n/a

Overall 8/9 n/a

4. OCD patients and healthy controlsAndrés et al. (2007) Rey Complex Figures OCD patients (n=35) Healthy controls (n=35) 2/2 n/aBehar et al. (1984) Rey Complex Figures OCD patients (n=16) Healthy controls (n=16) 0/1 n/aBoon, Ananth, Philpott, Kaur,and Djenderedjian (1991)

Rey Complex Figures OCD patients (n=20) Healthy controls (n=16) 1/1 n/a

Cha et al. (2008) Rey Complex Figures OCD non-checkers (n=23) Healthy controls (n=20) 0/2 n/aChang, McCracken, andPiacentini (2007)


Cox, Fedio, and Rapoport (1989) Rey Complex Figures OCD patients (n=42) Healthy controls (n=35) 2/2 n/aDeckersbach, Otto, Savage, Baer,and Jenike (2000)

Rey Complex Figures OCD patients (n=17) Normative data 2/2 n/a

Martinot et al. (1990) Rey Complex Figures OCD patients (n=14) Healthy controls (n=8) 1/1 n/aMataix-Colis et al. (2003) Rey Complex Figures OCD patients (n=30) Healthy controls (n=30) 3/4 n/aMoritz et al. (2003) Rey Complex Figures OCD patients (n=32) Healthy controls (n=20) 0/2 n/aMoritz et al. (2005) Rey Complex Figures OCD patients (n=71) Healthy controls (n=30) 0/2 n/aPenadés, Catalán, Andrés,Salamero, and Gastó (2005)


Roh et al. (2005) Rey Complex Figures OCD patients (n=21) Healthy controls (n=20) 6/6 n/aSavage et al. (1999) Rey Complex Figures OCD patients (n=20) Healthy controls (n=20) 3/4 n/aSavage et al. (2000) Rey Complex Figures OCD patients (n=33) Healthy controls (n=30) 2/2 n/aSegalàs et al. (2008) Rey Complex Figures OCD patients (n=50) Healthy controls (n=50) 3/3 n/aShin et al. (2004) Rey Complex Figures OCD patients (n=30) Healthy controls (n=30) 3/4 n/aSimpson et al. (2006) Rey Complex Figures OCD patients (n=30) Healthy controls (n=35) 0/2 n/aChristensen, Won Kim,Dysken, and MaxwellHoover (1992)

Corsi Block Tapping OCD patients (n=18) Healthy controls (n=18) 0/1 n/a

Galderisi et al. (1995) Corsi Block Tapping OCD patients (n=22) Healthy controls (n=21) 0/1 n/aMoritz et al. (2003) Corsi Block Tapping OCD patients (n=32) Healthy controls (n=20) 1/1 n/aMoritz et al. (2005) Corsi Block Tapping OCD patients (n=71) Healthy controls (n=30) 0/1 n/aPurcell, Maruff, Kyrios, andPantelis (1998)


Zielinski, Taylor, and Juzwin(1991)


Aronowitz et al. (1994) Benton Visual Retention OCD patients (n=31) Healthy controls (n=22) 2/2 n/aCohen et al. (1996) Benton Visual Retention OCD patients (n=65) Healthy controls (n=32) 2/2 n/aSimpson et al. (2006) Benton Visual Retention OCD patients (n=30) Healthy controls (n=35) 2/2 n/aAndrés et al. (2007) WMS-Visual Reproduction OCD patients (n=35) Healthy controls (n=35) 1/2 n/aBoon et al. (1991) WMS-Visual Reproduction OCD patients (n=20) Healthy controls (n=16) 0/2 n/aChristensen et al. (1992) WMS-Visual Reproduction OCD patients (n=18) Healthy controls (n=18) 1/2 n/aChristensen et al. (1992) WMS-Paired-Associates OCD patients(n=18) Healthy controls (n=18) 0/1 n/aPenadés et al. (2005) WMS-Faces OCD patients (n=33) Healthy controls (n=33) 0/1 n/aRadomsky and Rachman (1999) WMS-Visual Memory OCD patients (n=10) Healthy controls (n=20) 0/1 n/aAigner et al. (2007) Facial Recognition OCD patients (n=40) Healthy controls (n=40) 4/6 n/aChamberlain et al. (2007) Pattern Recognition Memory OCD patients (n=20) Healthy controls (n=20) 1/2 n/aDirson, Bouvard, Cottraux,and Martin (1995)

Signoret's Memory Efficiency Battery OCD patients (n=26) Healthy controls (n=20) 3/6 n/a

Jelinek et al. (2006) RBMT — Pictures and Faces OCD patients (n=31) Healthy controls (n=33) 0/2 n/aSavage et al. (1996) Delayed Recognition Span OCD patients (n=20) Healthy controls (n=20) 1/6 n/aZielinski et al. (1991) Recurring Figures OCD patients (n=21) Healthy controls (n=21) 2/8 n/aPurcell et al. (1998) Proprietary OCD patients (n=23) Healthy controls (n=23) 1/1 n/a

(continued on next page)(continued on next page)


Table 3 (continued)


Purcell et al. (1998) Proprietary OCD patients (n=23) Healthy controls (n=23) 1/1 n/aPurcell et al. (1998) Proprietary OCD patients (n=23) Healthy controls (n=23) 1/1 n/aPurcell et al. (1998) Proprietary OCD patients (n=23) Healthy controls (n=23) 0/1 n/aMoritz, Kuelz et al. (2006) Subjective Neurocognition Inventory OCD patients (n=67) Healthy controls (n=30) n/a 0/1Tolin et al. (2001) Proprietary OCD patients (n=14) Healthy controls (n=14) 0/18 4/18

Overall 53/116 4/19

5. OCD patients and psychiatric controlsChamberlain et al. (2007) Pattern Recognition Memory OCD patients (n=20) Psychiatric controls (n=20) 1/2 n/aChang et al. (2007) Rey Complex Figures OCD patients (n=16) Psychiatric controls (n=15) 0/2 n/aCohen et al. (1996) Benton Visual Retention OCD patients (n=65) Psychiatric controls (n=17) 0/2 n/aMoritz et al. (2005) Corsi Block Tapping OCD patients (n=71) Psychiatric controls (n=33) 0/1 n/aMoritz, Kuelz et al. (2006) Subjective Neurocognition Inventory OCD patients (n=67) Psychiatric controls (n=30) n/a 0/1Radomsky and Rachman (1999) WMS-Visual Memory OCD patients (n=10) Psychiatric controls (n=10) 0/1 n/aTolin et al. (2001) Proprietary OCD patients (n=14) Psychiatric controls (n=14) 1/18 2/18

Overall 2/26 2/19

a Data are not available.


deficit in the OCD checkers. The table also lists 18 comparisons of OCDcheckers' and OCD non-checkers' visual/spatial meta-memory, one ofwhich was significant.

The 2nd section of Table 3 shows four comparisons of the visual/spatial memory test performance of sub-clinical checkers and non-checkers, one of which was significant. As evident from Table 3, ourliterature search did not uncover any studies which have examinedthe visual/spatial meta-memory scores of sub-clinical checkers andnon-checkers.

The 3rd section of Table 3 lists nine comparisons of the visual/spatial memory test performance of OCD checkers and healthycontrols. Eight of these nine comparisons revealed a deficit in theOCD checkers. As shown in this section of the table, our search of theliterature did not reveal any studies that have explored the visual/spatial meta-memory scores of OCD checkers and healthy controls.

The 4th section of Table 3 shows that there have been 116statistical comparisons of the visual/spatial memory test performanceof OCD patients and healthy controls, 53 of which were significant. Inaddition, there have been 19 statistical comparisons of these twogroups' visual/spatial meta-memory, four of which were significant.

The bottom section of Table 3 shows that of the 26 comparisons ofthe visual/spatial memory test performance of OCD patients andpsychiatric controls, only two revealed a deficit in the OCD patients.Similarly, of the 19 comparisons of the visual/spatial meta-memoryscores of these two groups only two were significant.

2.1.4. Memory for verbal materialsFor the same reasons as given in connection with memory for

visual/spatial materials, we have an abundance of data on checkers'and OCD patients' memory for verbal materials. One curiousdifference between Tables 3 and 4 is the greater use of proprietarymethods for assessing verbal than visual/spatial memory. However,this difference does not seem critical because the literature shows thatmost proprietary tests differ from themore familiar standardized testsprimarily by virtue of the to-be-remembered spoken words orsentences they employed.

As shown in the top portion of Table 4, we identified 17 com-parisons concerning the verbal memory test performance of OCDcheckers and OCD non-checkers, none of which showed a significantdifference in favor of the memory deficit theory. In addition, welocated four comparisons concerning the verbal meta-memory scoresof OCD checkers and OCD non-checkers, and none of those wassignificant.

The 2nd section of Table 4 lists 19 statistical comparisons of theverbal memory test performance of sub-clinical checkers and non-checkers, and only one of these reached significance. The table showsthat there have been four statistical comparisons of these groups'

verbal meta-memory, none of which indicated a significant deficit inthe sub-clinical checkers.

The 3rd section of Table 4 enumerates 15 comparisons of the verbalmemory test performance of OCD checkers and healthy controls, nineof which were significant. As shown in the table, our review revealedseven comparisons of the verbal meta-memory of these two groups,five of which indicated a meta-memory deficit in OCD checkers.

The 4th section of Table 4 identifies 114 comparisons of the verbalmemory test performance of the OCD patients and healthy controlsand 29 of these were significant. In addition, there have been 15comparisons focused on OCD patients' and healthy controls' meta-memory, five of which showed a significant deficit in the OCD patients.

The final section of Table 4 lists 21 comparisons of the verbalmemory test performance of OCD patients and psychiatric controls,none of which revealed a significant deficit. As shown in the table, oursearch of the literature only uncovered one comparison focused on themeta-memory scores of these two groups and it was not significant.

2.2. Summary and discussion

The main findings from Tables 1–4 are highlighted in Fig. 1. Tocomplement the tables where the results from each section aresummarized as fractions, Fig. 1 shows the same data as proportions,with the left panels of the figure showing the findings relevant to thememory deficit theory and the right panels summarizing the findingsrelevant to the meta-memory deficit theory. The figure highlightssimilarities and differences between memory deficits and meta-memory deficits. It also shows similarities and differences across thememory domains (e.g., action memory, source memory) as well asacross the different subject group comparisons (e.g., OCD checkersversus OCD non-checkers).

A detailed account of similarities and differences in the findingsseems premature because of the absence or dearth of data in somecells, and because of the vast differences in the number of attemptsthat have been made to address each memory domain or subjectgroup difference. Nevertheless, the top two panels of Fig. 1, con-cerning memory and meta-memory related to action and sourcememory, show a fair number of statistical comparisons for most cells.For nearly all subject group comparisons (e.g., OCD checkers versusOCD non-checkers), these panels show larger deficits in meta-memory than in memory, suggesting that the former may be morestrongly affected in OCD, and underscoring the importance ofdistinguishing between the memory deficit theory and the meta-memory deficit theory.

Our search of the literature revealed an adequate amount of datafor nearly each cell of the panels on the left side of Fig. 1, therebypermitting cautious performance comparisons across the different

Table 4A summary of the results of research on verbal memory.


1. OCD checkers and OCD non-checkersCeschi, Van der Linden, Dunker,Perroud, and Brédart (2003)

California Verbal Learning OCD checkers (n=16) OCD non-checkers (n=16) 0/4 n/a

Cha et al. (2008) Hopkins Verbal Learning OCD checkers (n=24) OCD non-checkers (n=23) 0/2 n/aJelinek et al. (2006) RBMT — Name and Story OCD checkers (n=23) OCD non-checkers (n=8) 0/4 n/aOmori et al. (2007) WMS-Verbal OCD checkers (n=27) OCD non-checkers (n=26) 0/1 n/aKaradag, Oguzhanoglu, Ozdel,Atesci, and Amuk (2005)

Proprietary OCD checkers (n=22) OCD non-checkers (n=10) 0/4 0/4

Macdonald, Antony, Macleod,and Richter (1997)


Overall 0/17 0/4

2. Sub-clinical checkers and non-checkersRoth and Baribeau (1996) WMS-Logical Memory Sub-clinical checkers (n=14) Non-checkers (n=14) 0/2 n/aSher et al. (1984) WMS-Logical Memory Sub-clinical checkers (n = a) Non-checkers (n = a) 1/1 n/aSher et al. (1989) WMS-Logical Memory Sub-clinical checkers (n=13) Non-checkers (n=12) 0/1 n/aSher et al. (1984) WMS-Paired-Associates Learning Sub-clinical checkers (n = †) Non-checkers (n = †) 0/1 n/aSher et al. (1989) WMS-Paired-Associates Learning Sub-clinical checkers (n=13) Non-checkers (n=12) 0/1 n/aRubenstein et al. (1993) Exp 2 Proprietary Sub-clinical checkers (n=19) Non-checkers (n=20) 0/3 n/aRubenstein et al. (1993) Exp 3 Proprietary Sub-clinical checkers (n=19) Non-checkers (n=20) 0/2 n/aSher et al. (1983) Proprietary Sub-clinical checkers (n=26) Non-checkers (n=28) 0/2 0/1Tuna, Tekcan, andTopçuoğlu (2005)

Proprietary Sub-clinical checkers (n=16) Non-checkers (n=15) 0/6 0/3

Overall 1/19 0/4

3. OCD checkers and healthy controlsCeschi et al. (2003) California Verbal Learning OCD checkers (n=16) Healthy controls (n=16) 2/4 n/aCha et al. (2008) Hopkins Verbal Learning OCD checkers (n=24) Healthy controls (n=20) 0/2 n/aZitterl et al. (2001) LGT-3 OCD checkers (n=27) Healthy controls (n=27) 1/1 n/aMacdonald et al. (1997) Proprietary OCD checkers (n=10) Non-checkers (n=10) 0/2 n/aMacdonald et al. (1997) Proprietary OCD checkers (n=10) Non-checkers (n=20) n/a 2/4Tuna et al. (2005) Proprietary OCD checkers (n=17) Non-checkers (n=15) 6/6 3/3

Overall 9/15 5/7

4. OCD patients and healthy controlsCeschi et al. (2003) California Verbal Learning OCD non-checkers (n=16) Healthy controls (n=16) 2/4 n/aChang et al. (2007) California Verbal Learning OCD patients (n=16) Healthy controls (n=15) 0/3 n/aDeckersbach et al. (2000) California Verbal Learning OCD patients (n=17) Normative data 6/7 n/aDeckersbach et al. (2004) California Verbal Learning OCD patients (n=30) Healthy controls (n=30) 2/4 n/aMartin et al. (1993) California Verbal Learning OCD patients (n=17) Healthy controls (n=16) 2/6 n/aSavage et al. (2000) California Verbal Learning OCD patients (n=33) Healthy controls (n=30) 6/8 n/aZielinski et al. (1991) California Verbal Learning OCD patients (n=21) Healthy controls (n=21) 1/9 n/aAndrés et al. (2007) Auditory Verbal Learning OCD patients (n=35) Healthy controls (n=35) 0/2 n/aBehar et al. (1984) Auditory Verbal Learning OCD patients (n=16) Healthy controls (n=16) 0/1 n/aCox et al. (1989) Auditory Verbal Learning OCD patients (n=42) Healthy controls (n=35) 0/2 n/aJurado, Junqué, Vallejo,Salgado, and Grafman (2001)

Auditory Verbal Learning OCD patients (n=27) Healthy controls (n=27) 0/6 n/a

Jurado, Junqué, Vallejo,Salgado, and Grafman (2002)


Kitis et al. (2007) Auditory Verbal Learning OCD patients (n=23) Healthy controls (n=22) 0/3 n/aMartinot et al. (1990) Auditory Verbal Learning OCD patients (n=14) Healthy controls (n=8) 1/1 n/aRoth, Baribeau, Milovan,O'Connor, and Todorov (2004)


Cha et al. (2008) Hopkins Verbal Learning OCD non-checkers (n=23) Healthy controls (n=20) 0/2 n/aAndrés et al. (2007) WMS-Logical Memory OCD patients (n=35) Healthy controls (n=35) 1/2 n/aBoon et al. (1991) WMS-Logical Memory OCD patients (n=20) Healthy controls (n=16) 0/2 n/aChristensen et al. (1992) WMS-Logical Memory OCD patients (n=18) Healthy controls (n=18) 0/1 n/aChristensen et al. (1992) WMS-Paired-Associates Learning OCD patients (n=18) Healthy controls (n=18) 0/1 n/aRadomsky and Rachman(1999)

WMS-Verbal Memory OCD patients (n=10) Healthy controls (n=20) 0/1 n/a

Dirson et al. (1995) Signoret's Memory Efficiency Battery OCD patients (n=26) Healthy controls (n=20) 0/6 n/aJelinek et al. (2006) RiBMT — Name and Story OCD patients (n=31) Healthy controls (n=33) 0/4 n/aSavage et al. (1996) Delayed Recognition Span OCD patients (n=20) Healthy controls (n=20) 0/6 n/aSawamura, Nakashima,Inoue, and Kurita (2005)

Iddon's Verbal Strategy OCD patients (n=16) Healthy controls (n=16) 4/4 n/a

Segalàs et al. (2008) Spain-Complutense Verbal Learning OCD patients (n=50) Healthy controls (n=50) 4/6 n/aDirson et al. (1995) Proprietary OCD patients (n=26) Healthy controls (n=30) 0/3 n/aJurado et al. (2001) Proprietary OCD patients (n=27) Healthy controls (n=27) 0/5 n/aKaradag et al. (2005) Proprietary OCD patients (n=32) Healthy controls (n=31) 0/4 3/4Macdonald et al. (1997) Proprietary OCD non-checkers (n=10) Non-checkers (n=10) 0/2 0/4Moritz et al. (2007) Proprietary OCD patients (n=28) Healthy controls (n=28) 0/1 2/6Moritz, Kuelz et al. (2006) Subjective Neurocognition Inventory OCD patients (n=67) Healthy controls (n=30) n/a 0/1

Overall 29/114 5/15

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Table 4 (continued)


5. OCD patients and psychiatric controlsCeschi et al. (2003) California Verbal Learning OCD Non-Checkers (n=16) Psychiatric Controls (n=16) 0/4 n/aChang et al. (2007) California Verbal Learning OCD Patients (n=16) Psychiatric Controls (n=15) 0/3 n/aDeckersbach et al. (2004) California Verbal Learning OCD Patients (n=30) Psychiatric Controls (n=30) 0/4 n/aMartin et al. (1993) California Verbal Learning OCD Patients (n=17) Psychiatric Controls (n=11) 0/6 n/aKitis et al. (2007) Auditory Verbal Learning OCD Patients (n=23) Psychiatric Controls (n=24) 0/3 n/aMoritz, Kuelz et al. (2006) Subjective Neurocognition Inventory OCD Patients (n=67) Psychiatric Controls (n=30) n/a 0/1Radomsky and Rachman (1999) WMS-Verbal Memory OCD Patients (n=10) Psychiatric Controls (n=10) 0/1 n/a

Overall 0/21 0/1


memory domains. Findings in Fig. 1 highlight the similarity in thepattern of deficits related to action and source memory (the top twoleft panels), as well as the similarity in the pattern of deficits related tovisual and verbal memory (the bottom two left panels). In addition,however, the figure also highlights the difference in the pattern ofdeficits and the consistently larger deficits related to visual and verbalmemory compared to action and source memory.

The different pattern and larger deficits concerning visual and verbalmemory than action and sourcememorywas unexpected, but it may beanartifact related to the reliability and/or sensitivity of themethods andinstruments used for assessingperformance ineachmemorydomain.Asdescribed in Tables 1–4, most previous investigations have employed

Fig. 1. Proportion of comparisons revealing a memory deficit (left side) and meta-memocomparison. Note: The numbers above the bars indicate the total number of relevant comp

proprietary instruments for assessing action and source memory,whereas visual and verbal memory have typically been probed bymeans of standardized tests or by tests closelymodeled on standardizedtests. It is possible that the standardized tests are more reliable andsensitive than the proprietary tests (note: reliability data are availableformost standardized tests but not for the proprietary action and sourcememory tests), and that these differences might account for thedifferent size and pattern of deficits we found concerning visual andverbal memory than action and source memory. A more provocativealternative possibility is that individuals with OCDmay develop varioustechniques and strategies for supportingmemory in the context of theireveryday life, and these techniques and strategies might translate more

ry deficit (right side) in each domain of memory and for each type of subject grouparisons made.

Table 5A summary of the results of research on prospective memory.

Test OCD group Comparisongroup

Memorydeficit

Meta-memorydeficit

1. OCD checkers and OCD non-checkersMoritz,Kuelz et al.(2006)

SubjectiveNeurocognitionInventory

OCD checkers(n=30)

OCD non-checkers(n=37)

n/a 0/1

Overall n/a 0/1

2. Sub-clinical checkers and non-checkersCuttler andGraf (2007)

PMQ Sub-clinicalcheckers(n=40)

Non-checkers(n=45)

n/a 4/4

Cuttler andGraf (2008)

PMQ Sub-clinicalcheckers(n=64)

Non-checkers(n=62)

n/a 4/4


PRMQ Sub-clinicalcheckers(n=40)

Non-checkers(n=45)

n/a 1/1


PRMQ Sub-clinicalcheckers(n=64)

Non-checkers(n=62)

n/a 1/1


Proprietary Sub-clinicalcheckers(n=40)

Non-checkers(n=45)

1/1 0/1



Non-checkers(n=45)

0/1 0/1



Non-checkers(n=62)

1/1 n/a

Overall 2/3 10/12

3. OCD checkers and healthy controlsn/a n/a

Overall n/a n/a

4. OCD patients and healthy controlsMoritz,Kuelz et al.(2006)


OCD patients(n=67)

Healthy controls(n=40)

n/a 0/1

Overall 0/2 0/1

5. OCD patients and psychiatric controlsMoritz,Kuelz et al.(2006)


OCD patients(n=67)

Psychiatric controls(n=40)

n/a 0/1

Overall 0/2 0/1


readily to the types of naturalistic tasks thathave beenused forassessingaction and source memory than to the more sterile and controlleddemands of the standardized instruments which have been used forassessing visual and verbal memory. Future research is required todistinguish between these possibilities.

The most important findings in Fig. 1 concern differences in theperformance and in the meta-memory scores of OCD checkers versusOCD non-checkers, and the second most important findings concernthe differences in sub-clinical checkers versus non-checkers. For thereasons enumerated and discussed earlier in this report (i.e. becausecomparisons between these groups implicate the fewest possibleconfounds), comparisons between these subgroups bear most directlyon the specificity of the memory deficit theory and of the meta-memory deficit theory. The findings – the two leftmost bars of eachpanel – either show no deficits in the memory or meta-memoryscores, or they show only relatively small deficits in either thememory performance or meta-memory scores. Combined across allmemory domains, a total of 93 comparisons of the memory testperformance of OCD checkers and OCD non-checkers have been madeand only two showed a deficit in OCD checkers. Similarly, a total of 75statistical tests have been used to find memory deficits in sub-clinicalcheckers versus non-checkers, and only 13 showed a deficit. Withrespect to meta-memory there have been a total of 42 comparisons ofOCD checkers and OCD non-checkers and only five revealed thepredicted deficit. An additional 29 comparisons have addresseddeficits in the meta-memory of sub-clinical checkers and non-checkers, five of which revealed the predicted deficits. This balanceof findings does not bode well for either the memory deficit theory orthe meta-memory deficit theory.

A few cells in Fig. 1 seem at odds with this description of thefindings. The most notable exceptions are the high incidence ofdeficits in meta-memory for source information in the sub-clinicalcheckers, and the relatively high incidence of deficits inmeta-memoryfor action in the OCD checkers relative to OCD non-checkers. Althoughthese specific exceptions are provocative, they must be viewedcautiously because they are based on a relatively small number ofcomparisons (five and 10, respectively), and the bulk of the evidencewhich favors the theory was contributed by just two independentstudies (see Tables 1 and 2).

The higher incidence of memory performance deficits found incomparisons of sub-clinical checkers and non-checkers than incomparisons of OCD checkers and OCD non-checkers, depicted inthe two leftmost columns of Fig. 1, also must be interpreted cautiously.As discussed earlier in this report, comparisons between sub-clinicalcheckers and non-checkers are known to involve variables (e.g.,distractibility, depression, anxiety) that have the potential toconfound the results. We speculate that such confounds areresponsible for the more frequent occurrence of deficits in compar-isons between sub-clinical checkers and non-checkers than incomparisons between OCD checkers and OCD non-checkers.

By stark contrast to the absence or infrequent deficits in memoryand meta-memory found in studies which have compared OCDcheckers with OCD non-checkers or sub-clinical checkers with non-checkers, Fig. 1 underscores the far greater incidence of deficits foundin studies which have compared OCD checkers or OCD patients withhealthy controls. On the performance side of Fig. 1, those deficits areespecially pronounced in visual and verbal memory, whereas on themeta-memory side, deficits are pronounced in action and verbalmemory. A direct comparison of the findings in the 3rd (thoseshowing deficits in OCD checkers relative to healthy controls) and 4th(those showing deficits in OCD patients relative to healthy controls)columns of bars seems, at first glance, to indicate that deficits aremorecommon in OCD checkers than OCD patients.

A comparison of the findings in the 1st (those showing deficits inOCD checkers relative to OCD non-checkers) and 3rd (those showingdeficits in OCD checkers relative to healthy controls) columns of bars

in Fig. 1 shows that deficits are much more commonly found whenOCD checkers are compared to healthy controls than when they arecompared to OCD non-checkers. This finding highlights the impor-tance of using a matched control group and suggests that the deficitsthat have been discovered through comparisons of OCD checkers andhealthy controls are a function of the many potential confoundsinherent in such comparisons (e.g., medication, brain dysfunction,comorbid psychopathology). The same methodological messageabout the selection of appropriate control groups is underscored bythe difference in the findings summarized in the 4th (those showingdeficits in OCD patients relative to healthy controls) and 5th (thoseshowing deficits in OCD patients relative to psychiatric controls)columns of bars in Fig.1. Deficits aremore commonly foundwhenOCDpatients are compared to healthy controls than when they arecompared to psychiatric controls. Together these findings suggestthat the deficits that have emerged in some previous studies usinghealthy control groups are largely spurious and that they should notbe used as evidence to support the memory deficit or meta-memorydeficit theories.

The research summarized in Fig. 1 is in line with the recent reviewby Woods et al. (2002), showing that memory performance deficitsandmeta-memory deficits are a common occurrence in OCD checkers.

Table 6


More importantly, however, our review shows that such deficits areinfrequent in studies which have compared OCD checkers with OCDnon-checkers. Similarly, we have shown that such deficits areinfrequent in studies that have compared sub-clinical checkers withnon-checkers. Therefore, the combined findings from our reviewargue against the theoretical claims that memory deficits or meta-memory deficits contribute to the compulsion to check. In our view,the evidence does not support either the memory deficit theory or themeta-memory deficit theory of checking.1

Is it time to abandon these theories? Despite the foregoingconclusion, we recommend against this kind of rash step, first,because to the best of our knowledge, a total of only 15 empiricalinvestigations have specifically compared OCD checkers with OCDnon-checkers, and many of these studies involved relatively smallsamples. Moreover, while for most of these studies establishedinventories were used to classify patients as checkers or non-checkers,these groups are often overlapping and the possibility that some of theOCD non-checkers experienced some degree of checking compulsionscannot be ruled out. A second important reason against rejection ofthememory deficit andmeta-memory deficit theories comes from thefact that these theories have so far been examined in only a limiteddomain. Checking compulsions are typically initiated because ofanxiety generated by intrusive doubts pertaining to the failure toperform an intended action, such as locking a door. While checkers'ability to reach back and remember performing intended actions (i.e.,action memory) has been the focus of previous investigations,checkers' ability to reach forward and remember to execute intendedactions (i.e., prospective memory) has not yet been adequatelyinvestigated.

3. Memory deficits and meta-memory deficits inprospective memory

Our search of the literature revealed only four studies that haveexamined prospective memory in checkers and/or OCD patients. Oneof these studies was excluded from our review (Jelinek, Moritz,Heeren, & Naber, 2006) because of the presence of ceiling effects oneach of the prospective memory tests. The results of our review of theremaining three studies are arranged as they were in the previoussection on retrospective memory; they are summarized in a table(Table 5) which highlights results pertaining to memory and meta-memory. As so little research has been conducted in this domain, in anattempt to provide some preliminary insights into the specificity ofcheckers' putative prospective memory deficits the Results sectionalso presents some supplementary analyses of data from two of ourrecent studies.

3.1. Results

The studies listed in Table 5 used proprietary tests to assessprospective memory. For instance, we (Cuttler & Graf, 2007, 2008)used a modified version of a test from the Rivermead BehavioralMemory Test (RBMT) battery (Wilson, Cockburn, & Baddeley, 1985)which requires participants to request the return of a personalbelonging. Meta-memory for prospective memory has been assessedusing proprietary tests where participants have to estimate how wellthey will perform on prospective memory tests and also by means ofquestionnaires which are designed to measure the frequency ofexperiencing prospective memory failures in everyday life.

1 While the available evidence indicates that deficits in retrospective memory ormeta-memory do not contribute to the etiology of checking compulsions recentresearch suggests that, in healthy individuals, the act of checking can lower confidencein memory for the checked tasks (Van den Hout & Kindt, 2003a,b; Van den Hour &Kindt, 2004). Although Hermans et al. (2008) failed to extend these findings to asample of OCD patients, Van den Hout et al.’s intriguing results suggest that checkingcan actually increase doubt and may help to explain its repetitious nature.

As shown on the top portion of Table 5, there have been nocomparisons of the prospective memory test performance of OCDcheckers and OCD non-checkers. However, there has been onecomparison of OCD checkers' and OCD non-checkers' meta-memory,and it showed no differences in the scores of the two groups.

The 2nd portion of Table 5 lists three comparisons of theprospective memory test performance of sub-clinical checkers andnon-checkers and two of those showed a significant deficit in the sub-clinical checkers. The table also shows that there have been 12comparisons of the meta-memory scores of sub-clinical checkers andnon-checkers, 10 of which revealed a deficit in sub-clinical checkers.

The 3rd section of Table 5 shows that there have been nocomparisons of the prospective memory or meta-memory of OCDcheckers and healthy controls.

Similarly, the 4th section of Table 5 shows that there have been nocomparisons of the prospective memory test performance of OCDpatients and healthy controls. However, there has been one compar-ison of the meta-memory of OCD patients and healthy controls and itwas not significant.

The bottom section of Table 5 shows that there have also been nocomparisons of the prospective memory test performance of OCDpatients and psychiatric controls. The table shows that there has beenone comparison of the meta-memory of these two groups and it wasnot significant.

3.1.1. Supplementary analysesThe paucity of research on prospective memory provides little fuel

for speculation about the specificity of prospective memory andmeta-memory deficits to checkers. Thus, we conducted some supplemen-tary analyses on the data from two of our studies (Cuttler & Graf, 2007,2008) in order to determine whether prospective memory and meta-memory deficits are specific to checkers or are also present inwashers.Washing compulsions are the second most prevalent form ofcompulsive behavior (Henderson & Pollard, 1988; Rachman, 2002)and these compulsions commonly co-occur with checking compul-sions (Rachman, 2002; Rachman & Hodgson, 1980). In our previousstudies, we used the Padua Inventory (Sanavio, 1988) to assessobsessive–compulsive behaviors. Fortunately, this inventory containsa checking and a washing (contamination) subscale. By pooling ourtwo samples and using the criteria presented in Table 6, we were ableto obtain decent sized samples of relatively pure checkers (n=26),washers (n=36) and controls (n=97).

As detailed in the original articles (Cuttler & Graf, 2007, 2008),participants in each study were assigned a prospective memory testwhich required them to request the return of a personal belongingwhen they were told “we have now finished all of the tests.”Participants who requested the return of their belonging upon theoccurrence of this spoken cue were scored as successful andparticipants who failed to give the reminder at the appropriatemoment were scored as failing. As depicted in Fig. 2, checkersperformed significantly worse than controls on the prospectivememory test, χ2 (1)=6.24, pb .05. However, washers' performanceon this test was similar to controls, χ2 (1)=.00, pN .05. Of primaryimportance, checkers performed significantly worse than washers onthis test, χ2 (1)=4.32, pb .05.

Classification criteria and mean Padua Inventory subscale scores for checkers (n=26),washers (n=36) and controls (n=97).

Checkers Washers Controls

Criteria Mean (SD) Criteria Mean (SD) Criteria Mean (SD)

Checking score N10 16.92 (3.49) b10 5.47 (2.12) b10 4.34 (2.89)Washing score b10 6.73 (2.31) N10 16.53 (5.30) b10 6.47 (2.46)

Fig. 2. Failure rates (+SE) on the prospective memory test for controls (n=97),washers (n=36) and checkers (n=26).


To assess meta-memory, participants in each study completed theProspective Memory Questionnaire (PMQ; Hannon, Adams, Harring-ton, Fries-Dias, & Gibson, 1995). The PMQ contains four subscales,three which focus on the frequency individuals experience differenttypes of prospective memory failures (episodic, habitual, internallycued) and one which focuses on individuals' use of prospectivememory aiding strategies (e.g., reminders). Higher scores on the firstthree subscales indicate more frequent prospective memory failuresand higher scores on the memory aiding strategies subscale indicatemore frequent use of memory aiding strategies. Results from the PMQare shown in Fig. 3. They show that compared to controls, checkersreport significantly more failures on the episodic prospective memoryscale, t (121)=−2.66, pb .05, the habitual prospective memory scale,t (121)=−5.17, pb .05, and the internally cued prospective memoryscale, t (121)=−3.97, pb .05. Our previously reported finding thatcheckers give higher ratings on the memory aiding strategies scale(Cuttler & Graf, 2007, 2008) failed to reach significance in this reducedsample of checkers, t (121)=−1.40, pN .05. In contrast, washers didnot report more failures than controls on the episodic prospectivememory scale, t (131)=− .79, pN .05, the habitual prospectivememory scale, t (131)=− .51, pN .05, the internally cued prospectivememory scale, t (131)=−1.92, pN .05, or the memory aidingstrategies scale, t (131)=−1.48, pN .05. Moreover, compared towashers, checkers reported significantly more failures on the habitualprospective memory scale, t (60)=− .3.26, pb .05. The differencesbetween checkers' and washers' ratings on the episodic prospectivememory scale, t (60)=− .1.48, pN .05, the internally cued prospectivememory scale, t (60)=−1.66, pN .05, and the memory aidingstrategies scale, t (60)=− .09, pN .05, failed to achieve significance.

As an additional measure of meta-memory, participants in eachstudy completed the Prospective and Retrospective Memory Ques-tionnaire (PRMQ; Smith, Della Salla, Logie, & Maylor, 2000). ThePRMQ contains two subscales, one which focuses on the frequency ofexperiencing prospective memory failures and one which focuses on

Fig. 3. Mean ratings (+SE) on the four subscales of the Prospective MemoryQuestionnaire (PMQ) for controls (n=97), washers (n=36) and checkers (n=26).

the frequency of experiencing retrospective memory failures. Thus, forboth subscales higher scores indicate more frequent memory failures.As illustrated in Fig. 4, the results from the prospective memorysubscale of the PRMQ are consistent with the results of the PMQ.Checkers reported experiencing significantly more prospective mem-ory failures than controls, t (1)=−3.38, pb .05, while washersreported experiencing these failures at a similar frequency as controls,t (1)=− .86, pN .05. The difference between checkers and washersfell just short of the conventional level of significance, t (1)=−1.96,p=.054. Consistent with the findings of our reviewof the literature onretrospective memory, checkers and washers both reported experien-cing significantly more retrospective memory failures than controls, t(1)=−2.01, pb .05 and t (1)=−2.14, pb .05, respectively, and theratings of checkers and washers did not differ, t (1)=− .38, pN .05.

3.2. Summary and discussion

In connection with prospective memory, the literature pertainingto the memory deficit and meta-memory deficit theories of compul-sive checking is too small to reach any strong conclusions. To date,only two studies have examined the memory deficit theory in thecontext of prospective memory and both used sub-clinical, rather thanOCD, checkers. While all three of the reviewed studies examinedmeta-memory deficits, only one examined these deficits in OCDpatients. Clearly, more research with OCD patients is required.Research comparing the prospective memory test performance andmeta-memory scores of OCD checkers and OCD non-checkers isparticularly needed.

While scant, the existing evidence pertaining to the memorydeficit theory is promising in the domain of prospective memory.Results of the two studies (listed in the 2nd section of Table 5) thatfocused on prospective memory test performance indicate that sub-clinical checkers have deficits in this domain. Moreover, results of thesupplementary analyses showing that checkers demonstrate greaterdeficits in prospective memory test performance than either controlsor sub-clinical washers indicate that these deficits are unique tocheckers. This initial evidence for the specificity of prospectivememory deficits is encouraging and suggests that a deficit inprospective memory may hold the key to a better understanding ofthe compulsion to check. Indeed, checkers tend to become concernedwith and check whether they performed tasks whose successfulexecution depends on prospective memory (e.g., locking a door).Thus, checking compulsions may develop, in part, as a compensatoryreaction to a deficit in prospective memory. If individuals frequentlyforget to perform prospective memory tasks they may develop astrategy of checking to ensure that important tasks do not remainundone. Future research comparing the prospective memory testperformance OCD checkers and OCD non-checkers is clearly needed tofurther examine this possibility.

Fig. 4. Mean ratings (+SE) on the two subscales of the Prospective and RetrospectiveMemory Questionnaire (PRMQ) for controls (n=97), washers (n=36) and checkers(n=26).


Results pertaining to themeta-memory deficit theory in the domainof prospective memory are mixed. Moritz, Kuelz, Jacobsen, Kloss, andFricke (2006) used the prospective memory subscale of the SubjectiveNeurocognition Inventory to assessmeta-memory and failed to find anydeficits in OCD patients relative to either healthy or psychiatric controls.Moritz, Kuelz et al. also failed to find any differences in the scores of OCDcheckers and OCD non-checkers. Together, findings of their studyindicate that deficits in prospective related meta-memory are notpresent in, or unique to, checkers or OCDpatients. However, thefindingsfrom our research and supplementary analyses conflict with thisconclusion. We (Cuttler & Graf, 2007, 2008) used the PMQ and PRMQto assess meta-memory in the domain of prospective memory andfound that relative to non-checkers, sub-clinical checkers demonstratedeficits on each of the five subscales assessing meta-memory in thisdomain. The results of our supplementary analyses revealed nodifferences in the meta-memory scores of sub-clinical washers andcontrols. Moreover, sub-clinical checkers were found to exhibit greatermeta-memory deficits than sub-clinical washers, however only one ofthese effects reached conventional levels of significance. Thus, thefindings from our research indicate that meta-memory deficits in thedomain of prospective memory may be unique to checkers.

Inconsistent results pertaining to meta-memory may reflectdifferences in the populations tested. While Moritz, Kuelz et al.(2006) sampled from a population of OCD patients we sampled from asub-clinical population. While it is generally agreed that clinical andsub-clinical compulsions do not differ in any fundamental way (Gibbs,1996; Rasmussen & Eisen, 2002) it is possible that the mechanismsthat underlie sub-clinical and clinical checking compulsions differ. Itmay be that a deficit in prospective memory contributes to the morecommon and less severe form of sub-clinical checking compulsionsbut that separate factors contribute to the less common, more severe,and dysfunctional form of clinical checking compulsions. Futureresearch comparing OCD patients with checking compulsions, OCDpatients without checking compulsions, sub-clinical checkers andnon-checkers is needed to examine this possibility.

4. General discussion

Various versions of the memory deficit and meta-memory deficittheories of checking compulsions have circulated in the literature forover a century (Freud, 1909; Janet, 1903), but it was not until Sher etal.'s (1983) seminal contribution that researchers began empiricallyexamining the theories' assumptions. While previous reviewers havemade the critical first step of determiningwhethermemory andmeta-memory deficits are present in individuals with checking compulsions(Woods et al., 2002), the goal of our review was to examine whetherthere is evidence that memory deficits and/or meta-memory deficitsare unique to individuals with checking compulsions. Our review,which to the best of our knowledge was comprehensive, in so far as itcontains all studies which have directly compared the memory testperformance or meta-memory scores of OCD checkers and OCD non-checkers, sub-clinical checkers and non-checkers, and OCD checkersand healthy controls, offers two critical insights. The first insightpertains to methodology and the relevance of various control groups.The second insight is theoretical and pertains to the domains ofmemory inwhich the theories have been considered and investigated.

Much of what we know about checkers' memory deficits andmeta-memory deficits comes from studies which have involvedcomparisons between OCD checkers and healthy controls or betweensub-clinical checkers and non-checkers. However, our review showsthat the results of these comparisons can bemisleading and difficult tointerpret because they implicate a large number of potentialconfounds. While it is possible to identify many of these potentialconfounds and statistically control for them, future research focusedon understanding checking compulsions may be served better bydirect comparisons between OCD checkers and OCD non-checkers.

The most important insight gleaned from this review is that thememory deficit andmeta-memory deficit theoriesmay be too general.Little has been explicitly stated about the domain of memory that maybe impaired in checkers. Rather, previous investigators have assumedthat all there is to memory is retrospective memory and as a resultthey have focused almost exclusively on testing the theories in thisdomain. However, the results of our review show that deficits inretrospective memory are not specific to checkers and therefore donot hold the power to explain the compulsion to check. It is not toosurprising that previous investigators of thememory deficit andmeta-memory deficit theories have failed to consider prospective memoryas it is a relatively new and neglected field of research. However, theexamples that are commonly used to illustrate checking compulsionssuggest that these compulsions are linked to prospective memorytasks. The results of our review highlight a need to refocus attentionon this domain of memory, they suggest that deficits in prospectivememory are specific to checkers and therefore may hold the key to abetter understanding of the compulsion to check.

One promise for contextualizing and examining the memorydeficit andmeta-memory deficit theories in the domain of prospectivememory is that deficits in this domain may help to explain theintrusive doubts that typically instigate checking. In their usualformulation, the memory deficit and meta-memory deficit theoriesare unable to account for checkers' intrusive doubts about whethertasks were completed. The theories simply suggest that followingthese intrusive doubts, checkers have difficulty remembering per-forming the task or they do not trust their memory of performing thetask. However, by extending the memory deficit and meta-memorydeficit theories to the domain of prospective memory, we are able toexplain the occurrence of these intrusive doubts. If individuals withchecking compulsions have deficits in prospective memory and ahistory of prospective memory failures theymay begin to worry aboutand to have intrusive doubts concerning prospective memory failures(i.e., “did I unplug the iron?”). When the perceived consequences of aprospective memory failure are serious (e.g., the failure to unplug theiron after use might cause a fire), the fear of another failure maytrigger compulsive checking. Moreover, intrusive doubts may betriggered not only by the fear of objectively verifiable poor prospectivememory test performance but also by a person's lack of confidence inher/his prospective memory (i.e., by a meta-memory deficit).

Prospective memory is an exciting and largely uncharted domainof memory and a focus on this domain opens a number of potentialavenues for future research. Like retrospective memory, prospectivememory is not a unitary construct; it consists of clearly delineatedcomponents including episodic prospective memory, monitoring, andhabitual prospective memory (Graf & Uttl, 2001; Uttl, 2008). Episodicprospective memory tasks are those that need to be executed onlyonce, after a delay during which the intended action is not activelyheld in conscious awareness (Graf, 2005; Graf & Uttl, 2001;Kvavilashvili & Ellis, 1996; Meacham & Dumitru, 1976). An exampleis remembering to pick a friend up at the airport in two days.Monitoring tasks differ by virtue of the fact that the intended actionremains in conscious awareness during the brief retention interval(Graf & Uttl, 2001; Uttl, 2008). An example is remembering to stop thebath water before the tub overflows. Habitual prospective memorytasks differ from the latter two in that they need to be performed on aroutine, regular, or habitual basis (Graf & Uttl, 2001; Hannon et al.,1995; Kvavilashvili & Ellis, 1996; Meacham & Dumitru, 1976). Anexample is remembering to lock the door upon leaving home. Theexisting evidence for the memory deficit theory in the domain ofprospective memory has come exclusively from studies focused onepisodic prospective memory. Future research is needed to examinecheckers' performance on a wider variety of prospective memorytasks. Research on habitual prospective memory may be particularlyenlightening as the tasks that checkers tend to become concernedwith are best categorized as habitual prospective memory tasks (e.g.,


individuals need to lock doors on a routine basis) and the results ofour direct comparisons of sub-clinical checkers' and washers' meta-memory indicate that checkers have unique meta-memory deficits inthis component of prospective memory.

Future research should also focus on examining how memorydeficits andmeta-memory deficits interact with other factors believedto contribute to OCD. For instance, prevailing cognitive-behavioralmodels have emphasized the role of dysfunctional beliefs in theetiology andmaintenance of OCD (Clark, 2004; Frost & Steketee, 2002;Obsessive Compulsive Cognitions Working Group, 2005; Salkovskis,1996). OCD patients have been shown to be perfectionists, to beintolerant of uncertainty, to have an inflated sense of responsibilityand to overestimate the likelihood of threat (Obsessive CompulsiveCognitionsWorking Group, 2005). However, not all OCD patients holdthese dysfunctional beliefs (Taylor et al., 2006) and not everyone whohas a deficit in prospectivememory develops checking compulsions. Itseems unlikely that someone with a prospective memory deficitwould develop checking compulsions if they did not worry about theirfrequent prospective memory failures, feel responsible for them, orperceive their consequences to be serious. Rather, it seems that onlythose individuals who have a prospective memory deficit and whohold dysfunctional beliefs will develop checking compulsions. Wesuggest that checking compulsions occur if someone has frequentprospective memory failures, views them as unacceptable because ofperfectionistic standards and believes that failures could result incatastrophic outcomes for which they will be held responsible (e.g., “Iwill be responsible for the fire that will result if I left my iron on”).

Acknowledgments

This research was supported by operating grants from the NaturalSciences and Engineering Research Council of Canada to P. Graf and bygraduate scholarships to C. Cuttler from theMichael Smith Foundationfor Health Research and the Natural Sciences and EngineeringResearch Council of Canada.

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Checking-in on the memory deficit and meta-memory deficit theories of compulsive checking

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