Our visual system is designed to allow us functioning in three-dimensional environment which is filled with light, shading, color, texture, and full of objects of different sizes at different distances. Most of us take vision for granted without realizing how complex and difficult task our brain is performing in order to correctly represent the "real outside world". Our perception is created by our brain's interpretation of visual information and sometimes it results in fascinating visual illusions. Our mind gets "actively" involved in interpreting the perceptual input rather than passively recording the input. It does not always accurately represent that input.