Everything moves and everything changes. The Greek philosopher Heraclitus once said: ‘There is nothing permanent except change.’ Motion is ingrained in life, though some objects move very quickly (such as electrons) and others so slowly (a growing tree, for instance) that they seem static.
Man has always been wondering about the nature of motion. Take a look at the vigorous and precise strokes portraying a galloping wild boar in a cave near Altamira, Spain. The prehistoric artist created the illusion of movement by using a dynamic or motion blur, as seen in some modern photographs: the two pairs of legs painted with lighter colors suggest the boar was running so fast that the artist ‘perceived’ more legs than the actual four.
Not only was the portrayal of motion the purpose of this painting, it may also have been the expression of a very early curiosity from the artist as to why he or she was seeing more legs than the number that were known to be there. However, persistence of vision and the blurring effect would actually not be understood for several millennia!
In the world of optical illusions, the terms ‘autokinetic illusion’ or ‘apparent motion’ are used to describe the convincing appearance of movement in a picture that the viewer knows to be static. This particular form of visual trickery has a long history. The Ancient Romans were aware of how to create the illusion of movement, applying their knowledge of optics and perspective to create amazing illusive mosaic floors that fool the eye into thinking they are rotating slightly.
I will now introduce you to a new concept of optical illusions involving expansive motion created by/with parallel arrangements of cuspidate (needle-shaped) lines.
As shown below, two opposite sets of parallel arrangement of cuspidate lines interpenetrate leaving a blank space delimited by the outline of a heart (or by any other arbitrary shape).
When the pink shape is removed, the dark heart will start to pulsate and/or expand! (Moreover, if you stare for a while at it and close your eyes you will see a white heart appearing in your head!)
This optic effect by its nature is quite opposite from the other illusion called “Troxler’s fading” or “vanishing effect”, but it works in the same way. The solid central ‘black heart’ is not expanding at all, as it is rather the outer surrounding which looks like a blurred halo - outlined with red dotted lines - , that is slowly shrinking (in fact, dissolving) due to lower visual stimulus in comparison with the striped background and the plain black zone, giving thus the impression the solid black heart expands and pulsates.
The illusion works even with complex contours: the black bat featured below seems to flutter, pulsate and/or expand...
Color may also enhance the overall self-moving effect!