Abstract

Illusory figures have been explained by several models as due to the presence of two-dimensional interposition cues. The present work was aimed at testing whether such a figural condition is really necessary for the formation of illusory figures. The strength of illusory figures with and without clear interposition cues - indentations or angles in the inducing contours - was measured as point of subjective equality (PSE) by the method of adjustment. Results showed that the figure with angular indentations and the one without do not induce a significantly different effect, whereas both produce a stronger effect than that induced by the control figure of very weak inductive power. Such results challange all models based on the idea that interposition cues are necessary for the induction of illusory figures.