Vision-for-action in unilateral neglect: “virtual” grasping influences visual exploration of spatially displaced stimuli

Vision-for-action and vision-for-perception have been depicted as different processes supported by partially different neural networks, a dorsal or a ventral one. While lesions in the inferior parietal region, included in the ventral network, often result in unilateral neglect, lesions in the dorsal pathway are usually not associated to that syndrome. Vision-for-action may be preserved in neglect patients (Milner & McIntosh, 2004) and the clinical practice may capitalize on it. We investigated dissociations between vision-for-action and vision-for-perception in such patients. Three patients and ten control subjects completed a virtual-grasping gap-bisection task, imagining grasping an object between two spheres while we recorded their eye-movements (pure fixation and asymmetry indexes). Gaps differed in their spatial location (5 levels, from extreme left to extreme right). The clinical group did not show a clear right-side bias contrary to what we found in a previous study on vision-for-perception, where patients showed a bias particularly in left-positioned gaps (Balconi et al., 2010). Patients globally made more fixations than controls but the clinical and control groups seem to have a similar visual exploration: a cross-effect is evident, with more and longer fixations in the right hemifield when the gap was placed on the left and viceversa. Nevertheless, the fixations length asymmetry index did not show such cross-effect in patients. Results support the hypothesis of a partially preserved vision-for-action pathway in the clinical group. Comparing significant effects with previous evidences, we discuss them at the light of visual processing and attention control theories.