Optical and Neural Mechanisms in the Vertical-Horizontal Illusion

In psychophysical experiments, the discrimination of line lengths in the vertical-horizontal illusion and the dependence of Landolt ring separation to distractors in the crowding effect at the resolution limit of the visual system were compared separately for the same orientations. In the vertical-horizontal illusion, the length of the lines and their location were changed. In the crowding effect, Landolt Cs were surrounded by four bars (distractor) located symmetrically at different separations from the rings. The observers’ task was to identify orientation of the ring. The agreement of the obtained results was shown: the magnitude of the vertical-horizontal illusion is greater in the case of a pronounced difference in the vertical and horizontal orientations in the crowding effect. The principles of agreement of optical factors and organization of receptors on the retina and receptive fields of neurons of the visual cortex are analyzed. The influence of physiological astigmatism on the vertical-horizontal illusion is revealed, and the individual differences of the illusion are shown in observers with normal visual acuity. Possible mechanisms of the vertical-horizontal illusion are discussed.