Metric Properties of the Visual Illusion of Intersection

Abstract

The work is devoted to an experimental investigation of the well-known optical-geometric Poggendorff illusion (of the intersection illusion). With a visual perception of the intersection of the line with the opaque strip, an error arises due to inadequate extrapolation of the line continuation after passing through the strip. Experimental computer researches of factors influencing the existence and magnitude of illusion have been carried out. The main factors: the strip width, the strip orientation and the line inclination angle relative to the strip. After presenting a part of the line in front of the strip (of the “input fragment”) on the computer screen, the subject had to draw a line after the passage through the strip (“output fragment”) with the mouse. The following characteristics were measured: the displacement along the strip of the line “output fragment” and its direction. It is shown that the illusion exists irrespective of the spatial orientation of the screening strip, its color and texture. Quantitative estimates of the dependence of the illusion value on the strip width and the line inclination angle are obtained. Regression models of functional dependences of the illusion value from these factors are constructed. The effect of accumulating the illusion value at the intersection by the line of several parallel strips was studied also (the subjects had making subjective correction independently for each fragment of the line between the strips). The test revealed additive properties of Poggendorff’s illusion. The conducted researches made it possible to form a hypothesis combining the manifestations of Poggendorff’s illusion independently of the action of various factors, namely: there is a steady tendency to shorten the distance between the point of the “entrance” of the line into the strip area and the point of its “exit.” The field of practical applications, where optical illusions should be given great attention, is engineering psychology, medical engineering and education.