Vision-for-perception and vision-for-action in unilateral neglect: implications for rehabilitation

Introduction/Objectives: Unilateral neglect patients show difficulties in consciously processing information in the contralesional perceptual hemifield. It has been suggested that visual-processing for action or for perception involves different neural networks, a dorsal or a ventral one. While lesions in the ventral network often result in neglect, lesions in the dorsal pathway are usually not associated to that syndrome. This study aims at exploring specific dissociations between vision-for-action and vision-for-perception in such patients by using eye-movement measures. Participants, Materials/Methods: Three patients showing left neglect were compared to 10 matched controls in two gap-bisection tasks. During the perceptual task, participants were asked to evaluate the distance between two endpoints and to indicate the midpoint of the gap. During the virtual-motion task, participants were asked to imagine grasping an object between two endpoints and to indicate the midpoint of the gap. The gaps varied in length. Results: Eye-fixation indexes have been analyzed and statistically compared. During the perceptual task, patients showed a right-side bias in visual behaviour, in particular for longer gaps. During the virtual-motion task, instead, we have not found evidences for a similar bias: the clinical and control groups differed only in fixations count as a function of the gap length without specific effects for right/left hemifields. Conclusions: Evidences of a task-related effect on visual behaviour suggest interesting hints for rehabilitation of spatial exploration: vision-for-action may be preserved in neglect patients. Moreover, fixation data seem to be sensitive indexes for the assessment and may be used to increase patients’ deficit awareness.