Saccade control in natural images is shaped by the information visible at fixation: evidence from asymmetric gaze-contingent windows

When people view images, their saccades are predominantly horizontal and show a positively skewed distribution of amplitudes. How are these patterns affected by the information close to fixation and the features in the periphery? We recorded saccades while observers encoded a set of scenes with a gaze-contingent window at fixation: Features inside a rectangular (Experiment 1) or elliptical (Experiment 2) window were intact; peripheral background was masked completely or blurred. When the window was asymmetric, with more information preserved either horizontally or vertically, saccades tended to follow the information within the window, rather than exploring unseen regions, which runs counter to the idea that saccades function to maximize information gain on each fixation. Window shape also affected fixation and amplitude distributions, but horizontal windows had less of an impact. The findings suggest that saccades follow the features currently being processed and that normal vision samples these features from a horizontally elongated region.