Analysis of task demands in apraxia.

Several task demands were examined in a battery of praxis tests: the movement system (limb versus axial), input modality (command versus imitation), movement complexity (single gestures versus a sequence of gestures), type of limb gesture (transitive versus intransitive), and the representational nature of the gestures. Performance accuracy for a group of left hemisphere patients was significantly lower than for two other groups of patients with either right hemisphere damage or no brain damage on all gestures. The right hemisphere patients were significantly different from the normals only for the most complex gestures involving a three movement sequence. Within the left hemisphere group performance to command was not different from imitation. Representational and nonrepresentational gestures were not different, and axial gestures was not different from the limb gestures. The transitive and complex gestures were not different but were both performed less accurately than the intransitive gestures. The implications of these findings for understanding apraxia were discussed.