STEREOKINETIC EFFECTS WITH SHARP AND FUZZY ILLUSORY CONTOURS

A black, 8-shaped pattern, whose centre of gravity is in the centre of a rotating disc, appears to split into two black discs rotating with phenomenal independent motion, orientation stability, and sliding of o ne on the other, The type of observed movement, the order of overlappi ng, and the extent of the stereokinetic depth in relation to the conto ur type and different dimensions of the pattern were investigated. The experimental data show that a fuzzy contour facilitates the stereokin etic effect, Furthermore, the extent of the stereokinetic depth has be en found to be greater in case of fuzzy contour and vertical orientati on of the pattern. These results are in contrast with the models in wh ich this effect is considered as a problem of minimisation of distance s or velocities. A vector model of the observed movement and an interp retation of the overlapping based on an energy approach are proposed. A tentative explanation of the stereokinetic depth for our patterns is put forward.