Scanning the visual world: a study of patients with homonymous hemianopia

Objectives-This study examined the scanpaths of patients with homonymous he mianopia while viewing naturalistic pictures in their original and also spa tially filtered forms. Features of their scanpaths with respect to various saccade and fixation parameters were examined to determine whether they dev elop compensatory eye movement strategies. The effects of various lesion pa rameters including location, size, and age on the evolution of such strateg ies were considered. Methods-Eye movements of eight patients with homonymous hemianopia (four le ft, four right), but lacking neglect, were recorded while they viewed 22 im ages of real scenes, and they were compared with the eye movements of eight age matched controls. Subjects viewed each image for 3 seconds, initially in a spatially filtered form in which much of the semantic content had been removed, and then in their unfiltered, original form. Results-Patients differed significantly front controls in various fixation and saccade parameters. For fixation parameters patients with hemianopia fi xated different spatial positions from controls, made more fixations which were more widely distributed and of shorter duration than controls, and spe nt a greater proportion of their total fixation time in the area correspond ing to their blind hemifield. They did not make significantly more refixati ons than controls. For saccade parameters patients made more saccades into their blind hemifield, these saccades having shorter latencies and shorter amplitudes than those made into their seeing field, and had longer scanpath s than control subjects. The amplitude of their first saccade was longer th an that of controls although its direction did not correlate simply with th e side of the field defect. Their mean saccade amplitude was similar to tha t of controls. Filtering out high spatial frequencies within images seemed to accentuate the described differences between eye movement characteristic s of hemianopes and controls. Scanpath differences correlated with increasi ng age but not location or size of lesions causing the hemianopia. Conclusion-Various features of scanpaths produced by hemianopes were differ ent from normal subjects. These differences correlated with lesion age and may reflect the evolution of a compensatory eye movement strategy.