The relationship between performance on multiple-object tasks and single-object tasks by left-hemisphere-damaged aphasic adults: Implications for the assessment of limb apraxia

Date of Completion

January 1997


Health Sciences, Speech Pathology|Health Sciences, Medicine and Surgery|Psychology, Cognitive




Two types of object-manipulation tasks, commonly used in the assessment of limb apraxia, were administered to 30 left-hemisphere-damaged aphasic (LHD) adults and 10 nonneurologically impaired control subjects. The tasks were: a multiple-object task (MOT) requiring the manipulation of several related objects (e.g., lighting a candle given a candle, a candle holder, and a match) and a single-object manipulation task (SOT) (e.g., lighting a match). Each of the subjects' responses were assigned to one or more of seven response categories. The response categories were Standard (in which the response met all criteria for a faultless response) and six Nonstandard categories. (Clumsy, Mislocation, Object Misuse, Perplexity, Omission, and Missequencing).^ The primary concern of the investigation was a comparison of performances on the MOT and SOT by the LHD subjects and the nature of the relationship between the two tasks. Task comparison showed significantly fewer Standard responses for the SOT (51%) than the MOT (77%). This finding is contrary to the commonly held view that multiple-object tasks are more difficult than single-object tasks.^ Analyses of the relationship between MOT and SOT resulted in strong correlations, loadings on the same two factors, and no evidence of dissociations between the two tasks on any of the response categories. The strong relationship and absence of dissociations between response categories across the SOT and MOT suggest that both tasks are mediated by the same neuropsychological processes. Two processes, as derived by factor analysis, were identified and interpreted to be a motor execution factor and a conceptual factor. The interpretation of the latter as a conceptual factor was confirmed by its strong correlation (Pearson $r=.61)$ with an independent measure of object knowledge.^ To the extent that the subjects in this study can be considered to be limb apractic, these results support the use of single-object tasks in the assessment of limb apraxia. No unique results were obtained from the administration of a multiple-object task. Also, the single-object task was the more sensitive task in the detection of responses traditionally attributed to limb apraxia. ^