Fixation patterns made during brief examination of two-dimensional images

Measurements were carried out of saccadic eye movements made during brief (3 s) examination of images which the observer was asked to identify. Each image was identified in three forms: low-pass filtered, high-pass filtered, and unfiltered. The analysis of the eye-movement patterns was based on the locations of fixations made during examination of the images, for which purpose a least-squares measure of similarity between two sets of locations was introduced. It is shown that there is a high degree of similarity between fixations made by the same observer to the different versions of a given image and that for a given image there is a high degree of similarity between fixations made by the eighteen observers who participated in the experiments. The similarities are greater for the initial 1.5 s than for the full viewing period of 3 s. The similarity between the locations of fixations and those of selected image features such as local contrast, high-spatial-frequency content, and edge density was also examined. It is shown that there is only weak similarity between the locations of fixations and those of any given local image feature, and the tendency of observers to fixate centrally on the image is identified as the principal reason for the low similarity values. It is shown that if the nonuniform distribution of eye movements is taken into account, significant similarities are found between the locations of fixations and those of certain image features, such as edge density.