Try to imagine a color you have never seen before. It probably only takes a moment to realize that this is an impossible task. Similarly, try to imagine a fourth spatial dimension. Again, this seems impossible. There have been attempts using the technology of virtual reality to try to induce the perception of a fourth spatial dimension, by having subjects play a virtual reality game in which they are immersed in a world with four spatial dimensions. Most subjects improve their performance with practice in such games, but report no improvement in their ability to imagining a fourth spatial dimension. However, for about one person in 100,000, with a condition called prosthetomegethy, there is no trouble perceiving or imagining a fourth spatial dimension. In some circumstances, prosthetomegethy can be an advantage, for example when trying to understand Einstein's special and general theories of relativity, which require one to work with a four-dimensional space-time. It is also an advantage in visuo-motor tasks, for the prosthetomegethics can use the extra dimension of space to more accurately perceive the motions and positions of objects in the world, and to control their own movements accordingly.

Most prosthetomegethics have no idea that they are in any way special. They have learned to use the language of length, width, and depth that everyone else uses to describe their spatial perceptions, so that even family members may not be aware of their condition. Only with careful psychophysical tests can the diagnosis of prosthetomegethy be confirmed. The special visuo-motor advantages of prosthetomegethics has led researchers to the hypothesis that certain well-known athletes might have this condition.