Categorization of object descriptions in Alzheimer's disease and frontotemporal dementia: Limitation in rule-based processing

Abstract

Studies of semantic memory in probable Alzheimer's disease (AD) have focused on the degradation of semantic knowledge, but other work in AD suggests an impairment in the semantic categorization processes that operate on this knowledge. We examined the categorization of object descriptions, where semantic category membership judgments were based on rule-based or similarity-based categorization processes. We found that AD patients were selectively limited in their semantic categorization under conditions requiring a rule-based approach. However, AD patients did not differ from healthy seniors under conditions based on judgments of overall similarity. We showed that this was not due to nonspecific or overall task-related difficulty associatedwith the rule condition by asking the subjects to use similarity-based judgments of perceptually degraded versions of the stimuli. The results of this condition did not differ from other similarity-based judgments but did differ from the rule-based condition in AD. Rule-based judgments of semantic category membership correlated with executive measures of inhibitory control and mental search, but not with measures of episodic memory or overall dementia severity, suggesting a contribution of executive resources to rule-based semantic categorization. Moreover, the pattern of limited rule-based categorization in AD closely resembled the performance profile of patients with frontotemporal dementia, further implying that executive resource limitations underlie AD patients' limited rule-based semantic categorization. These findings suggest that semantic memory difficulty in AD is due in part to a deficit in executive processes that are central to rule-based categorization in semantic memory.

Categorization of novel tools by patients with Alzheimer's disease: Category-specific content and process

“…Neurologically intact adults successfully employed either process. AD patients were as successful at similarity-based categorization as their healthy counterparts, but were selectively impaired at rule-based categorization, in keeping with their impaired executive resources (LaFleche & Albert, 1995; Patterson et al, 1996; Grossman et al, 2003; Perry et al, 1999). Consistent with this, AD patients’ difficulty with rule-based processing correlated with their impairment on standard psychometric tests of executive function, while executive function was unrelated to patients’ similarity-based performance.…”

“…In addition to comparing results across the two processing conditions in the present novel tool study, we looked for comparisons and differences with our parallel novel animal study. As in that study, we anticipated that healthy seniors would be successful at using either categorization method (Allen & Brooks, 1991; Grossman et al, 2003; Patalano et al, 2001) and that AD patients would be impaired relative to controls. A different pattern of categorization success for tools compared to animals would suggest a role for content specificity in AD patients’ performance.…”

“…We have previously argued that semantic memory involves not only knowledge content such as items’ general appearance, features, and function, but also the processes by which such knowledge is assembled into coherent concepts (Grossman et al, 2003; Koenig & Grossman, 2007; Koenig et al, 2007; Koenig et al, 2006). We focused on categorization processes as the primary means by which this integration takes place because semantic memory generally entails identifying objects as members of a class (e.g., a dog ) rather than as unique individuals (e.g., “Fido”).…”

Verb acquisition and representation in Alzheimer's disease

“…Much evidence shows that patients with AD have semantic memory difficulty (Grossman et al, 2003a;Hodges, Patterson, Graham, & Dawson, 1996), perhaps due to degraded semantic knowledge (Garrard, Patterson, Watson, & Hodges, 1998;Garrard, Lambon Ralph, Patterson, Pratt, & Hodges, 2005;Silveri, Daniele, Giustolisi, & Gainotti, 1991) or to a deficit in processing semantic representations (Grossman et al, 2003b;Koenig et al, 2007;Koenig & Grossman, 2007). By comparison, assessments of grammar in AD associate difficulty with the working memory component of sentence processing (Grossman & WhiteDevine, 1998;Waters, Rochon, & Caplan, 1998).…”

Categorization Abilities for Emotional and Nonemotional Stimuli in Patients With Alcohol-related Korsakoff Syndrome

“…57 Behavioural and neuroimaging studies suggest that rule-based categorizations strongly depend on executive functioning whereas similarity-based categorizations mainly depend on successful prototype memory retrieval. [58][59][60] Due to the fact that we only observed correlations with executive functions in the EPT but not in SCT performance and only provided prototypes in the SCT, it might be that participants used similaritybased categorization processes on the SCT but rule-based categorization processes on the EPT. Nevertheless, performance in both tasks was correlated to measures of general knowledge (ie, long term-memory).…”