Review of cognitive performance in hoarding disorder
Introduction
Hoarding disorder is characterized by extreme difficulty discarding objects other people would typically discard (or recycle or donate). People generally engage in a fairly routine effort to balance perceived value of objects with the amount of space available to retain them. That is, items with high monetary, instrumental, or sentimental value are likely to be retained even when space is tight. In the case of hoarding, however, even objects of limited objective value are retained after the point when living spaces are too filled with clutter to be functional for their intended purposes. A hoarded home often has a chaotic appearance, with many possessions piled in disarray. Although individuals with hoarding disorder may not complain of having too many possessions, they frequently complain about difficulty finding their belongings or of possessions being damaged because they are not stored properly.
In an influential paper, Frost and Hartl (1996) proposed several cognitive processing deficits to be central to the development and maintenance of hoarding. On the basis of extensive clinical experience, Frost and Hartl argued that judgments of the value of possessions drive excessive acquisition and difficulty discarding, and their paper explored types of cognition that may influence those value judgments. Many of these cognitive processes are also relevant to the disorganization that gives rise to most of the functional impairment of hoarding.
Although the Frost and Hartl (1996) paper offers the most comprehensive theoretical position on cognitive processing in hoarding, several other researchers have also offered observations and predictions. Steketee and Frost (2003) reflected that information processing problems would most likely occur in relation to clutter and disorganization rather than excessive acquisition; certainly the preponderance of the research has examined this supposition. Grisham, Brown, Savage, Steketee, and Barlow (2007) proposed problems with planning and executing complex goal-directed motor responses in the face of potential emotional and environmental distractions would impair the ability to manage (i.e., organize and discard) possessions in the home.
This paper reviews the evidence related to these propositions and other executive functioning processes that have received research attention in the 15 years since Frost and Hartl offered their theory. In this paper, we are primarily interested in cognitive processes that can be, but are not always, studied using performance tasks. Frost and Hartl also made suggestions about beliefs (e.g., responsibility for being prepared to meet a potential future need) relevant to the phenomenon of hoarding. Although many of these factors, including the specter of post-decisional regret (Tolin & Villavicencio, 2011b), are probably important contributors to abnormal valuing in hoarding, those factors are beyond the scope of this paper.
In considering types of thinking that would influence judgments of value of (and decisions to keep) a given object, Frost and Hartl (1996) focused on decision-making, categorization/organization, and memory. Frost and Hartl suggested measurable deficits would be found in these areas, including slowed performance due to fear of making mistakes, higher thresholds for decisions to discard or lower thresholds for distinctiveness of objects belonging to a category, or poor memory confidence. We first review research that has examined the Frost and Hartl propositions in these domains and then move on to research on executive functioning deficits not specifically mentioned by Frost and Hartl. Following our review of the extant research, we offer some observations about the state of the literature, summarize the conclusions that can be drawn at this point, and suggest important areas for research attention.
Section snippets
Method
In order to provide a synthesis of the current knowledge available on hoarding and cognitive performance, the current review utilized a broad collection of search terms to identify studies from multiple areas of cognition. The PsychInfo, PubMed, and Google Scholar databases were electronically searched for literature in November 2011 and again in February and December 2013. The list of search terms used to identify these studies included “hoarding”, words related to cognitive domains of
Decision-making
In relation to decision-making, Frost and Hartl (1996) suggested fear of making mistakes, combined with uncertainty about the probability of needing an object in the future, would make it difficult to decide whether to discard objects. They proposed perfectionism would interfere with decision-making as individuals strive to find a solution that will satisfy all possible relevant factors, resulting in a prolonged process of weighing the pros and cons of each option. In addition, they expected
Categorization
A second type of general deficit Frost and Hartl (1996) proposed involves categorization or organization. Overall, the function of categorization is to more efficiently extract information from the environment (Rosch & Lloyd, 1978). Because stimuli can be differentiated on an infinite number of dimensions, categorization creates shortcuts for dividing stimuli into behaviourally and cognitive usable proportions. Reed, 1969a, Reed, 1969b proposed that individuals with obsessive–compulsive
Memory
Frost and Hartl (1996) proposed several problems involving memory that may be important to hoarding, but most of these problems involve metacognitive responses rather than memory per se. For example, Frost and Hartl suggested individuals who hoard may be overly inclusive in their judgments of what is important to remember, especially when perfectionism (remembering perfectly) is involved. Subsequent research shows that hoarding participants express less confidence in their own memory, report
Attention/working memory
Clinical experience and self-report research suggest the importance of examining inattention in the context of hoarding disorder. In their extensive clinical work with clients affected by hoarding, Hartl and Frost noted that many such clients carried previous diagnoses of attention deficit hyperactivity disorder (ADHD), and many others spontaneously complained of inattentive symptoms including failure to complete tasks, difficulty sustaining attention, disorganization, and procrastination (
Planning and perceptual organization
As mentioned earlier, Grisham et al. (2007) proposed hoarding involves problems with planning and executing complex goal-directed motor responses while controlling interference (e.g., environmental distractors, emotional responses). They suggested such problems would impair the ability to effectively organize and discard possessions in the home. The Tower of London and its computerized adaptation, Stockings of Cambridge, are tests of spatial planning that involve rearranging colored blocks or
Inhibitory control
Several researchers have examined impulsivity, or poor response inhibition, as a potential contributing factor to acquisition and saving behavior in hoarding. Although some of the tasks mentioned above require inhibitory control to perform well, the prototypical inhibitory control task is the widely used Stroop Color-word Interference Test. This task involves maintaining a goal in mind and suppressing a habitual response in favor of a less familiar one, requiring selective attention, response
Cognitive flexibility
The Wisconsin Card Sorting Task is a commonly used measure of set-shifting and cognitive flexibility. It requires the participant to discover implicit rules and shift strategies when those implicit rules change without announcement. Numerous outcome indicators can be obtained, including number of sorting categories completed, perseverative errors (in which the respondent persists in using the “old” rules after a shift), and failure to maintain set (errors made after a lengthy series of correct
Verbal performance
Numerous measures of verbal performance have been examined across studies, with results largely indicating hoarding participants perform similarly to healthy and clinical comparison groups. No differences have been observed on verbal fluency among children, adults or older adults (Mackin et al., 2011, Testa et al., 2011, Tolin et al., 2011). Tests of verbal reasoning and comprehension have shown no consistent differences, nor have tests of academic achievement or reading skills (Grisham et al.,
Summary of positive findings
Many tests of cognitive functioning have been administered in two or three studies, which typically have not yielded unanimous conclusions judged by effects of at least medium size. These differences among studies are likely due to methodological differences. Especially important are differences in diagnostic methods and inclusion criteria, a situation that is likely to improve now that DSM-5 has been published with hoarding disorder criteria. Furthermore, researchers do not always report the
Conclusions and future directions
Since 1996, when Frost and Hartl offered their theory of compulsive hoarding, there have been numerous investigations of the propositions contained in their seminal paper and of other cognitive processes that may be associated with hoarding behavior. The purpose of the current review is to synthesize results from these studies and draw some conclusions about what has been learned about cognitive processes that contribute to and maintain hoarding disorder. In this final section, we draw those
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The second and third authors contributed equally to this work.