Automatic control of saccadic eye movements made in visual inspection of briefly presented 2-D images

This paper describes an investigation of eye movements made by eighteen observers with normal spatial vision in response to eleven images of natural scenes each of which was presented in three versions, unfiltered, filtered by low-pass and filtered by high-pass spatial frequency filters. The ability of observers to identify the different images was determined after each set of measurements. An index of similarity, calculated in terms of the sum of the squares of the distances between each fixation point and its nearest neighbour in the other set, was developed in order to provide a basis for the comparison of two sets of eye movements, each made by a different observer or both made on different occasions by the same observer. Application of this index shows that for brief (1.5-s) presentation, there exists a high degree of similarity between fixations made by different observers in response to the same image. For longer (3-s) periods, however, the similarity for inter-observer comparisons is reduced. The data demonstrate that filtering of the image has little effect on the pattern of fixations made to a given image, but the duration of fixations is greatest for low-pass filtered images and least for unfiltered images, whereas the amplitude ;of saccades is greatest for unfiltered images and least for low-pass filtered images. It is proposed that for brief presentations, eye movements made during examination of an unfamiliar image are performed automatically in response to the spatial features of the image.