Visualizing Images In Your Head

[theBruiser500]

Always been curious about this. People say "close your eyes and imagine" etc. But when I close my eyes I can imagine stuff, but I don't see anything. Like my friend today is telling me he can visualize in his head clear images, like peole's faces. When I close my eyes I just see blackness though, and even when I try to see something I can't. What about you guys? Thoughts on this subject?