Characterising patterns of eye movements in natural images and visual scanning

A method to characterise the pattern of human eye movements as a person views a scene is developed. Rather than describe the spatial distribution of fixations, a new concept is introduced-crossing number-that uses a single number to describe the complexity of the eye scan. First a gaze pattern, i.e. the curve formed by joining all the points of fixation in consecutive order, is generated. The number of times that the curve crosses over itself is the total crossing number. In two different experiments free eye movements were measured during viewing of natural scenes and the performance of a specific visual task requiring an eye scan through a randomly positioned set of items. We demonstrate that there are sometimes large individual differences in crossing number that may reflect different scanning strategies used by different observers.