Spatial dynamics of the eggs illusion: Visual field anisotropy and peripheral vision

The eggs illusion is a visual phenomenon in which bright circular patches located at the midpoints between the intersections of a dark grid are perceived as being elongated along the direction orthogonal to the grid line. In the four experiments we report here, we explored the spatial properties of the eggs illusion by manipulating retinal eccentricity and the location of the stimulus in the visual field. In Experiment 1, we examined whether central and peripheral configurations affected the illusory magnitude. In Experiment 2, we varied the spatial location of grid patterns and found that the eggs illusion was intensified when the pattern was presented in the horizontal, not vertical or diagonal position, relative to the fixation. In Experiment 3, we varied the retinal eccentricity of the pattern along the horizontal meridian and found that the illusion was enhanced in the retinal periphery. In Experiment 4, we manipulated the size of the stimulus and found that peripheral enhancement of the eggs illusion was more apparent for a larger pattern. The visual field anisotropy and the peripheral enhancement of the eggs illusion are discussed in relation to mechanisms underlying grid-induced illusions.