Collinearity or correspondence between the contours of the inducing figure to allow `contour continuation' or `figure completion' were, according to G. Kanizsa, the necessary conditions for producing anomalous surfaces or contours. Since Kanizsa's early work various hypotheses have been advanced to explain the phenomenon, but very few examples of anomalous contours that do not satisfy the above conditions have been reported.
When two small white discs (1 cm in diameter) are set on a larger black disc in slow rotation, the two discs, after some observation time, will appear as the extremities of a rigid cylinder displaced in depth. The surface of the cylinder, under dim illumination, appears as a whitish transparent surface. However, when the two discs are substituted by a circle and a semicircle of the same size, a clear anomalous contour appears to form the cylinder, even under clear light conditions and when the colours are reversed; i.e., black circles on white disc. The anomalous contours are not apparent when the configuration is stationary. I will demonstrate how the anomalous contours of a stereokinetic cylinder can be obtained even without the “interruption” of the lines in the semicircle.
The relationship between the anomalous contours of the stereokinetic cylinder and the vitreous transparency of the surface of the cylinder formed by the two small discs above mentioned, will be discussed as well as their relation to the general theories of anomalous surfaces.