Distortion of auditory space in hemianopia

Abstract

Sound localization was investigated in patients with homonymous hemianopia, a visual field defect characterized by a loss of vision in one hemifield that is caused by unilateral brain lesions involving the visual cortex or its afferents. The primary aim was to clarify whether or not the known distortion of visual space in hemianopia results in processes of long-term cross-modal spatial adaptation, thus eventually inducing related alterations in auditory space perception. For this purpose, patients were tested by using tasks of either head pointing or manual pointing to acoustic targets in the azimuthal plane, under anechoic conditions in total darkness. The results obtained with both tasks consistently indicated slight, but significant, systematic errors compared with normal controls. In particular, the errors found can be interpreted by both rotation and compression of auditory space toward the anopic side. These findings can be explained by a visual miscalibration of the auditory space, as has been analogously demonstrated in studies on normal-sighted subjects after exposure to consistent auditory–visual disparity, for example by wearing prism lenses. The precision in sound localization of hemianopic patients was generally reduced across both hemispaces. Taken together, one may conclude that processes of cross-modal spatial adaptation, but not those of compensatory plasticity, occurred in patients with hemianopia.