Eye movements and fixation characteristics in perception of stationary scenes: normal subjects as compared to patients with visual neglect or hemianopia

Abstract

Saccade amplitudes, fixation times, and the spatial distribution of fixation points were comparatively studied in patients with visual hemineglect and/or homonymous hemianopia, as well as in normals (each group, n = 8). Two types of picture slides were presented (with and without search task) while eye movements were recorded with the infrared reflection technique. Self-developed software served to detect fixations, and to document their spatio-temporal parameters. Spectra of saccade amplitudes and fixation times were characteristic of each slide, while exhibiting notable similarities across subject groups. It is concluded that foveal information processing may not be much different in patients and in normals. Average saccade amplitudes and total scanpath lengths across all pictures were significantly smaller in the patients than in normals with both types of slides. In the neglect patients, saccades starting and terminating in the unaffected visual hemifield were larger, on an average, than those entirely located in the affected hemifield. The same was true for many of the hemianopic patients. Nevertheless, during free exploration, mean amplitudes of saccades restricted to the unaffected hemifield of the patients were apparently still smaller than those of normal controls within the corresponding hemifield. Average dwell time of fixations, total fixation time, as well as the total number of fixations did not vary significantly between groups. However, in the patient groups, average fixation times were shorter after large as compared to small saccades. This finding is discussed in the context of saccadic programming on the background of the sequential attention model of eye movement control. In subsamples of five hemianopic and six neglect patients, asymmetry in the distribution of fixation points was compared before and after a 4-week period of comprehensive rehabilitation that Included computerized scanning and attentional training. Only patients with pure hemianopia (who were less severely impaired from the beginning) improved according to this criterion, while neglect patients remained unchanged or deteriorated slightly. Total scanpath lengths, however, were not significantly different before and after therapy in any of the two groups of patients, indicating a persisting disturbance in scanning performance also in the hemianopic group.