Mirror images and unilateral spatial neglect.

Responding correctly to a mirror image requires the creation of a rather peculiar form of dual representation. Mirror agnosia and mirror ataxia, i.e. a deficit in reaching an object reflected in a mirror, have been reported to be associated with parietal lobe lesions. This prospective study was conducted to investigate the capacity of subjects with neglect to identify the mirror image nature of visual information. Four consecutive brain-damaged patients with neglect, selected on the basis of specific criteria, and four control subjects performed grasping and object displacement tests under two response conditions (normal mirror and inverted mirror). Video recordings of the tests were analyzed to assess performance using the following criteria: (i) direction of the arm movement during the initial phase of movement, (ii) number of corrections of the hand position before grasping. The control subjects successfully grasped the objects in both experimental conditions. The patients (1) neglected the contralesional space, grasping objects correctly in the ipsilesional space (normal mirror condition) and (2) neglected the ipsilesional space, grasping correctly objects in the contralesional space (inverted mirror). Controls used real object-centered correction clues to modify the position and direction of their hand movement. The patients only produced horizontal displacements of the upper limb in the "healthy" and neglected space. These results suggest that patients with neglect do not use the same clues and do not modify their procedures as they cannot recalibrate their spatial representations. These differences concerned non-mirror-image clues and directional and positional as well as attentional vectors. Theoretical and rehabilitative implications are discussed.