AOI hierarchies for visual exploration of fixation sequences.

In eye tracking studies a complex visual stimulus requires the definition of many areas of interest (AOIs). Often these AOIs have an inherent, nested hierarchical structure that can be utilized to facilitate analysis tasks. We discuss how this hierarchical AOI structure in combination with appropriate visualization techniques can be applied to analyze fixation sequences on differently aggregated levels. An AOI View, AOI Tree, AOI Matrix, and AOI Graph enable a bottom-up and top-down evaluation of fixation sequences. We conducted an expert review and compared our techniques to current state-of-the-art visualization techniques in eye movement research to further improve and extend our approach. To show how our approach is used in practice, we evaluate fixation sequences collected during a study where 101 AOIs are organized hierarchically.