ABSTRACT
A number of subjects observed squares of various sizes (15′ × 15′ up to 240′ × 240′). They were instructed to keep their direction of gaze within the square. Their eye movements, being so restricted, were recorded, analyzed and separated into drift and saccadic components. These components were simulated and used to move a uniformly bright square in a stabilization set-up to investigate their contributions for generating or preserving the percept of brightness. The influence of the retinal eccentricity of the stimulus contours was also investigated.
When increasingly larger squares were observed, only the subject's mean sac-cade amplitudes increased, whereas drifts did not. Drift movements arc effective in preserving vision only when stimulus contours are located in or near the foveal area. For larger stimuli saccades are needed as well. Intersubject differences and perceptual differences resulting from normal and simulated eye movements were also analyzed.
It is discussed how the small amplitude drifts and the larger amplitude saccades cooperate to preserve vision. The correlation of receptive (perceptive) field diameters and fading time constant, both increasing towards the periphery, are relevant for the understanding of the behavior of drifts and saccades in response to larger stimuli.
