In order to answer this you must first understand the idea of 'perception'. Perception refers to the interpretation of what we take in through our senses, in terms of optical illusions this means our eyes. Optical illusions occur because our brains our trying to interpret what we see and make sense of the world around us. Optical illusions simply trick our brains into seeing things which may or may not be real.
In order to make sense of the world, our brains try to see patterns or shapes that we can easily recognise. This principle is called 'grouping'. …
