Prism adaptation and unilateral neglect: review and analysis.

Theory and data from normal prism adaptation are applied toward understanding the ameliorating effects of prism adaptation for left unilateral neglect patients. Neglect is proposed to be, at least in part, a dysfunction in selection of the region of space appropriate for the task at hand. Normally, a task-work space is strategically sized and positioned (calibrated) around the task-relevant objects. Patients show deficits in both strategic abilities: the task-work space is pathologically reduced in size and patients cannot strategically shift its position. Prism adaptation (spatial realignment) ameliorates dysfunctional positioning, but not sizing of the task-work space. Realignment shifts the egocentric coordinates of a sensory-motor reference frame, thereby bringing at least part of the neglected hemispace into the dysfunctional task-work space: prism adaptation substitutes for dysfunctional positioning, but not sizing of a task-work space. However, such amelioration of dysfunctional positioning may enable relearning of strategic processes (calibration), perhaps, even partially restoring the ability to appropriately size the task-space. Investigation of therapeutic prism adaptation requires methods that permit identification of both the calibration dysfunction and ameliorating realignment.