Detection, Inspection and Re-Inspection: A functional approach to gaze behavior towards complex scenes

Abstract

Traditional approaches examining fixations towards natural scenes either focus on their spatial distribution, or aim to explain their exact sequence. Whereas heat-maps potentially conflate fixations serving different perceptual functions, scan-paths may aim for an unnecessary level of detail. Here, we introduce a novel way of analysing fixations. We hypothesize that fixations mainly serve three goals: Detection, Inspection and Re-Inspection of visual objects. Detection (D) for foveal vision is achieved by the first fixation landing on a given object, Inspection (I) by successive scanning immediately after Detection, and Re-Inspection (R) following the intermediate exploration of other objects. N = 101 participants freely viewed 700 images of everyday scenes. To test consistency within and differences between D, I and R fixations, we generated separate fixation maps for each category and image, separately for two subsets of observers. Results indicate large consistencies for D, I and R fixations across observers, with maps sharing 95%, 93% and 88% of their variance on average. At the same time, the shared variance between D, I and R was only 65% on average. To explore the nature of these differences, we computed the proportions of D, I and R fixations landing on different types of objects and found they could vary substantially. For instance, 57% of Inspection, but only 34% of Detection fixations landed on Text. Finally, we probed individual differences in the proportions of dwell time allocated to D, I and R. These individual biases towards D, I or R were both, considerable and highly consistent across images (all r > .96). Taken together, the DIR model can capture distinct aspects of fixation behavior on an observer-general and individual level. We propose it as a useful level of description for analysing and understanding the diverse perceptual functions of gaze behavior.