The distinction between a ventral visual processing stream devoted to processing object identity and a dorsal stream coding object location and body movements guides two decades of research in perception and action. A number of lines of evidence, including work from our laboratory, suggest that the model requires refinement. This work described in this proposal has two general aims. The first is to develop a model of the action system within a computational framework. The model includes two anatomically and functionally distinct components: the action representation system, mediated by the inferior parietal lobe, and the action execution system, mediated by dorsal stream structures in fronto-parietal cortex. The second general aim is to reconcile a major clinical syndrome, ideomotor apraxia (IM), with recent advances in the cognitive neuroscientific study of action. There are four specific aims. First, we will relate the diverse presentation of IM to the two components of the action system by evaluating a two-subtype model of lM. Second, through study of patients with IM, we will assess the distinction between two types of spatial coding of body position and body movement information. Third, we will assess the roles of objects in performing skilled movements, and the distinctions between object representations used in different contexts. Finally, we will elucidate internal models of movement used in programming actions. The proposed program of research is expected to continue to contribute to our understanding of the relationship of distinct representational and dynamic processing modules in normal and disordered action, and the neuroanatomic substrate for these processes. In addition, it is expected to significantly advance our understanding of lM, a common clinical disorder whose presentation, subtypes, and neuroanatomic substrate remain poorly understood. ? ?
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