Matching and imitation of hand and finger postures in patients with damage in the left or right hemispheres.

To disentangle perceptual, conceptual and motor aspects of imitation of gestures, reproduction of meaningless postures of either the hand or the fingers was examined in two conditions. In the matching test a target gesture had to be identified among an array of four gestures performed by different persons and seen under different angles of views. For imitation, the same gestures had to be imitated. Thirty-five patients with LBD, 21 patients with RBD, and 17 healthy controls were examined. LBD patients had more difficulties with imitation than with matching while RBD patients had more difficulties with matching than with imitation. Regardless of whether imitation or matching was tested, LBD patients made more errors with hand than with finger postures whereas RBD patients made more errors with finger than with hand postures. This constellation of results is compatible with the assumption that errors are caused by faulty visuoperceptual processing in RBD, and by defective conceptual mediation in LBD. Defective motor execution does not appear to be a significant source of imitation errors in either group.