14 October 2007

Iluzie optica: spinning silhouette

In ce directie se roteste imaginea de mai jos? Cei mai multi o vad rotindu-se in sensul acelor de ceas. Daca acoperi silueta si te uiti doar la umbra o poti face sa se roteasca si in directia inversa. Dupa o vreme schimbarea sensului de rotatie apare (la intamplare) si daca te uiti la toata imaginea, iar dupa mult "antrenament" o poti face in mod constient sa-si schimbe directia de rotatie. Explicatia pentru iluzie pare sa fie (Rishikesh Dalal):
The reason we experience the illusion is that the mind extrapolates the shadow into a 3-D object. The 3-D object could be either of two mirror images. We just don't know which mirror image to select. In fact, ANY object, regardless of its symmetry or non-symmetry can be transformed by reflection and will produce the same shadow when rotating in the opposite direction as the original. Basically just imagine reflecting the rotating object itself in a mirror - the reflected object will produce the same shadow but will be spinning in the opposite direction to produce the shadow. Our shillouhette is a perfect example of this in action - when spining clockwise, her right arm is outstretched and her head is tilted to her right. When spinning CCW, her left arm is outstretched and her head is tilted to her left. The two objects that we can extrapolate from the shadow are mirror images of each other. Most people see the clockwise rotation initially because we tend to perceive the feet as being closer to the observer when they are lower in the field of vision (as in everyday life).