gestalt principle of closure... in this principle, though the edges of the circle are not defined entirely, our minds continue the edges and it appears to be a white circle surrounded by spikes of various sizes
The fundamental principles (or laws) of perceptual organization were outlined by the Gestalt psychologists. They are proximity, similarity, good continuation, closure, smallness, surroundedness, and symmetry. The one above is surroundedness, which makes it seem as one figure is surrounded by the other. All laws serve the pragnanz principle, which is the simplest and most stable interpretations are favored.