Fixation and the Vertical-Horisontal Illusion

Abstract

The vertical-horizontal illusion was observed under two conditions: with fixation and without fixation. In the O-Condition (without fixation) the illusory effect—the overestimation of the vertical line—is at work alone. In the F-Condition (with fixation) the illusion is combined with the after-effect. The results indicate that the O-Condition had a significantly larger illusory effect than the F-Condition. It is concluded that the mechanisms underlying the vertical-horizontal illusion and the figural after-effect must be assumed to be different.