Auditory-Visual Localization in Hemianopia

Objective: Beyond visual field defects, patients with hemianopia have been suggested to perceive horizontal visual space in a distorted manner. However, the pattern of these distortions remained debatable. The aim of this study was to estimate the geometry of the visual representation of space in hemianopia using an auditory marker. Method: Patients with pure left or right hemianopia (without neglect) were tested in tasks requiring them to bring a visual stimulus into spatial alignment with a target sound (Experiment 1) or vice versa (Experiment 2). Results: In Experiment 1, patients adjusted the location of a light such that it was displaced toward the anopic side with reference to the physical sound position. In Experiment 2, patients adjusted the location of a sound such that it was displaced opposite to the anopic side with reference to the actual position of the visual target. Both experiments consistently indicated that hemianopic patients perceived a sound and a light to be in spatial alignment when the physical position of the light deviated by several degrees from the sound toward the side of the anopic hemifield, that IS, to the contralesional side. Conclusions: Given that auditory localization in patients with hemianopia has been previously shown to be only slightly biased toward the anopic side, the observed distortion of visual space with reference to auditory space can be explained by assuming that visual positions were, in absolute terms, perceived as shifted toward the intact side. As a result, HA patients may perceive visual space as compressed on their ipsilesional (intact), in comparison with their contralesional (anopic) side.