Actually the human brain is very accommodating when it comes to vision and spatial direction, so an inverted image can be reconciled quite easily if it is presented enough times, or for a long enough duration. In other words it can be learned. Once learned, it is for all intents and purposes "natural" to one who has acquired the skill. Look up the experiments of Dalibor Vesely if you find this interesting.
Originally Posted by David Nebenzahl