The tilt illusion: Repulsion and attraction effects in the oblique meridian

It is commonly believed that the same neural mechanism underlies the tilt illusion and the tilt aftereffect. Recently, it has been demonstrated that tilt aftereffects induced on oblique stimuli are similar, in magnitude and direction, to those induced on stimuli which are vertical or horizontal. If the mechanisms of the illusion and aftereffect are the same, then illusions induced on oblique stimuli should also be similar to those induced on vertical or horizontal stimuli. The six experiments reported here confirmed this prediction by suggesting that both repulsion (direct) and attraction (indirect) tilt illusions occur in the oblique meridian. The data are considered in relation to both psychophysical (normalisation) and neural (lateral inhibition) theories of orientation illusions and aftereffects.