Exploring power-law behavior in human gaze shifts across tasks and populations

Visual perception is an integral part of human cognition. Vision comprises sampling information and processing them. Tasks and stimuli influence human sampling behavior, while cognitive and neurological processing mechanisms remain unchanged. A question still controversial today is whether the components interact with each other. Some theories see the components of visual cognition as separate and their influence on gaze behavior as additive. Others see gaze behavior as an emergent structure of visual cognition that emerges through multiplicative interactions. One way to approach this problem is to examine the magnitude of gaze shifts. Demonstrating that gaze shifts show a constant behavior across tasks would argue for the existence of an independent component in human visual behavior. However, studies attempting to generally describe gaze shift magnitudes deliver contradictory results. In this work, we analyze data from numerous experiments to advance the debate on visual cognition by providing a more comprehensive view of visual behavior. The data show that the magnitude of eye movements, also called saccades, cannot be described by a consistent distribution across different experiments. However, we also propose a new way of measuring the magnitude of saccades: relative saccade lengths. We find that a saccade's length relative to the preceding saccade's length consistently follows a power-law distribution. We observe this distribution for all datasets we analyze, regardless of the task, stimulus, age, or native language of the participants. Our results indicate the existence of an independent component utilized by other cognitive processes without interacting with them. This suggests that a part of human visual cognition is based on an additive component that does not depend on stimulus features.