Eye movements tell only half the story

Abstract

Neglect due to right hemisphere injury, most commonly after stroke, continues to be a major cause of disability. Indeed, patients with neglect behave as if half of their world has ceased to exist. One means of improving the performance of patients with hemispatial neglect is to move stimuli into their body-centered ipsilesional space. Therefore, providing patients with 15 to 20-diopter Fresnel prisms might be simple means of shifting images to the normal side. To enhance the therapeutic effect of prisms, the subject can be trained to point straight ahead while wearing the prism. This procedure has been called prism adaptation. In this study, a subject with neglect used these prisms and was evaluated on two visual tasks before and after prism adaptation. Eye movements were recorded during the visual tasks. The authors demonstrated that while the exploratory eye movements of a patient with neglect were clearly shifted toward the left after prism adaptation, he still showed no awareness for the left side of the stimuli he was now actively exploring. The authors suggest that prism adaptation modulates functions of the parietal lobe, such as eye movement control, but fails to influence the underlying mechanisms of neglect.—Valérie Biousse