Cognition in action: testing a model of limb apraxia

Assessment of limb apraxia is still suffering from Liepmann's legacy and performance in gesture-processing tests is generally rendered by classifying patients' profile according to the classic clinical labels of ideomotor and ideational apraxia. At odds with other cognitive functions, interpretation of apraxia has suffered from a lack of a reliable model which does justice to its complexity. Recently such a model has been proposed (Rothi et al., 1991, 1997). In this article a modified version of this model is presented and predictions are made according to its functional architecture. Five different patterns of impairment of gesture processing are postulated. To validate the predicted performance profiles, 19 left-hemisphere-damaged patients were assessed by means of an ad hoc battery of four praxis tests. Four of the five predicted apraxia patterns were observed, the fifth being more equivocal. These results support the need to overcome the simplistic dichotomous view of apraxia and confirm the fruitfulness of a model of normal gesture processing in order to understand dissociations in apraxia.