VISUAL SCANNING BEHAVIOR IN PATIENTS WITH HOMONYMOUS HEMIANOPIA

This study examined oculomotor scanning behavior in 60 patients suffer ing from homonymous hemianopia due to postgeniculate damage. Eye movem ents were recorded using an infra-red recording technique during perfo rmance of a visual searching task. In 24 patients (40%) scanning behav ior was found to be normal; the remaining 60% showed significantly inc reased search times. Detailed analysis of patients' eye movements reve aled that the pronounced slowing of visual scanning was mainly due to the disordered spatial organization of scanning not only in the affect ed, but also, to a lesser degree, in the intact hemifield. CT and NMR examination revealed that additional damage to the ipsilateral posteri or thalamus or the parieto-occipital cortex results in impaired spatia l organization of visual scanning. A smaller group of patients (n = 14 ) with impaired visual scanning was treated to improve the spatial org anization of visual exploration. After training, all patients showed a significant improvement in visual searching, indicating that successf ul oculomotor adaptation can substitute the lost visual hemifield. It is argued that impaired visual scanning in hemianopic patients is main ly caused by visual spatial disorientation which also affects spatial integration of visual information processing.