A new optical geometrical illusion

The aim of the present work was to describe and attempt to explain a new and unusual geometrical optical illusion with three levels of distortion. The illusive figure was made up of three juxtaposed bands of the same width, which, when appropriately juxtaposed, appeared to be of different widths. We hypothesised that the effect would depend on the combined action of some factors: 1) the band shape and their reciprocal spatial position. 2) The degree of coincidence of the sides of the juxtaposed bands. 3) The perceptual system’s inability to account for all the projective transformation. To test these hypotheses, an experiment was conducted in which the shape of three stimuli was manipulated through affine transformation as well as variation of side lengths. The participants' task was to evaluate the width of the bands. The results revealed a robust and stable illusive effect and the factors that most seem to influence the illusion were band shape and conjoining side lengths.