Visualization FTW!

Im on a mission, and i need advice from anyone with information on the subject of visualization.
Ive had my fair share of lucid dreams and find im constantly suprised at how powerful the mind is when it comes to creating lifelike realistic scenes. What suprises me though is that when i try to visualize images in my mind im usually dissapointed with the results. Months back i looked into visualization and within a few weeks managed to get some amazing results. Im just starting practice again but wonder if anyone else has put time into this or if anyone knows how science explains the poor visualization ability of most people. I know if you look from an evolutionary side its obvious visualization skills wouldn't have benefited hunter gatherer humans, but that still doesnt explain the science behind why we cant visualize very well compared to maybe the sense of taste.
When i origionally looked into this i managed to get to a stage where i could achieve very vivid 'fullscreen' images that would jolt me out of them with excitement (like powerful HI that gives you that sudden quick heartbeat) and this was while fully concious but with my eyes closed.

Hope someone can supply some input, even if its just to warn me about possible mental health problems :-P .

>RooJ