Exploration and Exploitation in Natural Viewing Behavior

Many eye-tracking studies investigate visual behavior with a focus on image features and the semantic
content of a scene. A wealth of results on these aspects is available, and our understanding of the
decision process where to look has reached a mature stage. However, the temporal aspect, whether to
stay and further scrutinize a region (exploitation) or to move on and explore image regions that were
yet not in the focus of attention (exploration) is less well understood. Here, we investigate the trade-off
between these two processes across stimuli with varying properties and sizes. In a free viewing task, we
examined gaze parameters in humans, involving the central tendency, entropy, saccadic amplitudes,
number of fixations and duration of fixations. The results revealed that the central tendency and
entropy scaled with stimulus size. The mean saccadic amplitudes showed a linear increase that
originated from an interaction between the distribution of saccades and the spatial bias. Further, larger
images led to spatially more extensive sampling as indicated by a higher number of fixations at the
expense of reduced fixation durations. These results demonstrate a profound shift from exploitation to
exploration as an adaptation of main gaze parameters with increasing image size.