Looking for symmetry: fixational eye movements are biased by image mirror symmetry.
Humans are highly sensitive to symmetry. During scene exploration, the area of the retina with dense light receptor coverage acquires most information from relevant locations determined by gaze fixation. We characterized patterns of fixational eye movements made by observers staring at synthetic scenes either freely (i.e., free exploration) or during a symmetry orientation discrimination task (i.e., active exploration). Stimuli could be mirror-symmetric or not. Both free and active exploration generated more saccades parallel to the axis of symmetry than along other orientations. Most saccades were small (<2°), leaving the fovea within a 4° radius of fixation. Analysis of saccade dynamics showed that the observed parallel orientation selectivity emerged within 500 ms of stimulus onset and persisted throughout the trials under both viewing conditions. Symmetry strongly distorted existing anisotropies in gaze direction in a seemingly automatic process. We argue that this bias serves a functional role in which adjusted scene sampling enhances and maintains sustained sensitivity to local spatial correlations arising from symmetry.
Institut de Neurosciences de la Timone, UMR 7289 CNRS and Aix-Marseille Université, Marseille, France; School of Psychology, University of Western Australia, Crawley, Western Australia, Australia; and Psychology and Interdisciplinary Neuroscience Research Group, Faculty of Science and Technology, Bournemouth University, Fern Barrow, Poole, United Kingdom ameso@bournemouth.ac.uk.
Andrew Isaac
AI
Meso
Institut de Neurosciences de la Timone, UMR 7289 CNRS and Aix-Marseille Université, Marseille, France;
Anna
A
Montagnini
School of Psychology, University of Western Australia, Crawley, Western Australia, Australia; and.
Jason
J
Bell
Institut de Neurosciences de la Timone, UMR 7289 CNRS and Aix-Marseille Université, Marseille, France;
Guillaume S
GS
Masson
D004192:Discrimination, Psychological; D053483:Eye Movement Measurements; D005260:Female; D005385:Fingers; D005403:Fixation, Ocular; D006801:Humans; D008297:Male; D009043:Motor Activity; D010775:Photic Stimulation; D011601:Psychophysics; D012438:Saccades; D014796:Visual Perception
eye movements; gaze; mirror symmetry; saccades; visual sampling