Distance

"Sensation itself has no 'markers' for size and distance; these have to be learned on the basis of experience. Thus it has been reported that if people who have lived their entire lives in dense rain forest, with a far point no more than a few feet away, are brought into a wide, empty landscape, they may reach out and try to touch the mountaintops with their hands; they have no concept of how far the mountains are."

Oliver Sacks, An Anthropologist on Mars