Apraxia is an impairment in the ability to pantomime or imitate gestures usually caused by a stroke more frequently to the left than the right hemisphere. Due to the complex nature of apraxia, disruptions to a number of different cognitive and motor processes have been proposed to underly this disorder. In order to examine disruptions to these processes the participation of a special population of people who have suffered a stroke has been enlisted. The role of memory has been particularly well elucidated in studies of this special population, as patients with left hemisphere damage exhibit a particular deficit in performing gestures from memory. In this paper, through use of a model depicting the stages involved in gestural production, the processes that might be affected at each stage by left hemisphere damage are examined. The implications of the “cognitive neuropsychology” approach for incorporating special populations into research in the movement sciences are considered.
The frequency and characteristics of apraxia in 63 stroke patients with left- or right-hemisphere damage were examined. Analyses focussing on five dimensions of gestural performance revealed an overall frequency of apraxia of 54 % in patients with LHD and 30 % in patients with RHD. Although both groups were impaired on the orientation and hand posture dimensions of performance, the patients with RHD exhibited significantly poorer performance on the location dimension and the patients with LHD on the action dimension. Analyses of intrahemispheric lesion localization implicated damage to subcortical areas involving periventricular white matter tracts at the temporoparietal junction with apraxia.
Abstract Apraxia is thought to reflect a disruption to high-level perceptual, cognitive and motor systems that form a distributed praxis network. Some authors suggest that apraxic deficits are unique to the neurology clinic; however, mounting evidence suggests that apraxic deficits are observable in natural contexts (e.g. Foundas et al., 1995). Naturalistic gesture production involves the integration of conceptual knowledge, gesture ideation, visual and somatosensory cues, and executive processes. Impairments in this context are therefore of interest from a clinical and theoretical standpoint. We present the case of a young female stroke patient (CK) demonstrating a novel limb praxis profile. CK's conceptual, evocation and praxis executive stages were evaluated: performance was contrasted to 30 healthy controls. CK was able to pantomime and imitate transitive gestures, suggesting that her ideational, executive and visual analytic systems were intact. Moreover, CK showed a good conceptual understanding of tools, objects and actions. However, CK demonstrated poor gesture production when actually using the tool associated with the action – a chronic and bilateral deficit that persisted at a 5-year follow-up assessment. Thus, CK's deficit appears to represent a specific and chronic disruption to high-level praxis systems that incorporates tactile inputs into the unfolding gesture production sequence.
Past research suggests that the similarity between the objects associated with actions impacts visual action identification and action production. Indeed, people often confuse actions that are visually similar, as well as actions that are associated with visually similar objects. However, because the action errors often involve actions that are visually similar and are associated with visually similar objects, it is difficult to disambiguate between the influences of object similarity and action similarity. In our experiments, healthy participants were asked to learn to associate nonword names and actions with novel objects. Participants were first shown each object and its action and were then asked to visually identify each object. In Experiment 1, participants were then asked to produce the action associated with each object, and in Experiment 2, they were asked to visually identify the action associated with each object. Actions were confused more often when they were associated with similar objects than when they were associated with dissimilar objects. Furthermore, following an object naming error, participants were more likely to produce the action associated with the erroneous name than any other erroneous action. The results suggest that the visual characteristics of the objects influenced action production and action identification. ( JINS , 2007, 13 , 1021–1034.)
