This study examined the impact of irrelevant dimensional variation on rule-based category learning in patients with Parkinson's disease (PD), older controls (OC), and younger controls (YC). Participants were presented with 4-dimensional, binary-valued stimuli and were asked to categorize each into 1 of 2 categories. Category membership was based on the value of a single dimension. Four experimental conditions were administered in which there were zero, 1, 2, or 3 randomly varying irrelevant dimensions. Results indicated that patients with PD were impacted to a greater extent than both the OC and YC participants when the number of randomly varying irrelevant dimensions increased. These results suggest that the degree of working memory and selective attention requirements of a categorization task will impact whether PD patients are impaired in rule-based category learning, and help to clarify recent discrepancies in the literature.
Objective and Background: Previous studies have shown that patients with frontal-striatal dysfunction demonstrate improved performance on tests of recognition memory relative to free recall memory, suggesting deficits in retrieval processes. Not all studies, however, have indicated that all patients with frontal-striatal dysfunction display this profile. In this study, we examined the ubiquity of this ''retrieval deficit'' profile in a relatively large sample of patients with Parkinson disease (PD) or Huntington disease (HD).Methods: Participants included 150 patients with PD and 65 patients with HD. Patients were classified as demonstrating a retrieval deficit or not based on a comparison of their standardized performances on the Recognition Discriminability and Long-Delay Free Recall indices from the California Verbal Learning Test.Results: Results indicated that 1) a retrieval deficit was more prevalent in patients with HD than PD, 2) this group difference emerged only in patients with at least a mild level of global cognitive impairment, and 3) even when the profile did emerge more frequently in patients with HD, it was present in only 44% of the patients.Conclusions: These findings suggest that not all patient groups with frontal-striatal dysfunction display a retrieval deficit profile, but in groups that do (ie, patients with HD), it is more likely to appear in individuals with greater cognitive impairment.
This study investigated several constructs of executive functioning in a group of 77 patients with subcortical pathology. Specifically, we examined the validity of categorizing perseverative errors as "recurrent," "stuck-in-set," or "continuous," as proposed by Sandson and Albert (1984). A principal components analysis of 2 measures of recurrent perseveration, 2 measures of stuck-in-set perseveration, and 2 measures of intrusive errors yielded a 2 component solution with stuck-in-set perseverations and intrusive errors loading on Component 1, and recurrent perseverations loading on Component 2. Presence of a continuous perseveration on a graphomotor test was significantly associated with higher factor scores on Component 1, but not Component 2. The stuck-in-set perseveration and intrusion component was associated with the majority of the other neuropsychological tests administered, including tests of executive function and memory. The recurrent perseveration component was not associated with the other measures of cognitive functioning. Presence of a continuous perseveration was associated with executive function but not memory measures. This study provides evidence that recurrent perseverations are distinct from the other types of perseverative and intrusive errors, and that stuck-in-set and intrusive errors are good indicators of general cognitive functioning in patients with subcortical pathology.
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