Gaze allocation in natural stimuli: Comparing free exploration to head-fixed viewing conditions

Abstract

“Natural” gaze is typically measured by tracking eye positions during scene presentation in laboratory settings. How informative are such investigations for real-world conditions? Using a mobile eyetracking setup (“EyeSeeCam”), we measure gaze during free exploration of various in- and outdoor environments, while simultaneously recording head-centred videos. Here, we replay these videos in a laboratory setup. Half of the laboratory observers view the movies continuously, half as sequences of static 1-second frames. We find a bias of eye position to the stimulus centre, which is strongest in the 1 s frame replay condition. As a consequence, interobserver consistency is highest in this condition, though not fully explained by spatial bias alone. This leaves room for image specific bottom-up models to predict gaze beyond generic biases. Indeed, the “saliency map” predicts eye position in all conditions, and best for continuous replay. Continuous replay predicts real-world gaze better than 1 s frame replay does. In conclusion, experiments and models benefit from preserving the spatial statistics and temporal continuity of natural stimuli to improve their validity for real-world gaze behaviour.