Here again a plastic figure is deprived of its consistency as an object and represented as a flat image, likewise plastic but without illusory depths. Visual perception, however, has to take into account two virtual movements: one of the object and one of the subject, that is, of the eye. It is therefore necessary to make use of particular signs that imply certain allusions or suggestions. For example, the spiral has a sense of movement even though, as a flat image, it is simply a curved line. In this case it is precisely the spiral line that activates, as if they were springs, the yellow, black, and white ellipses.
But since movement can be given as a component of the image, though not in a real or an illusory manner, five horizontal and vertical elements have the function of blocking it.