I can't visualize things when I'm thinking consciously about them. But I do lucid dream, and when I lucid dream, I can visualise things perfectly. When I'm designing complex robotic mechanisms, lying in bed half awake in the morning is by far the most productive I'll be. I have no problem designing 3D mechanisms in CAD, or painting, and I tend to think of myself as a very visual person, but if I close my eyes and try to visualise something when fully awake, it somehow escapes me. But even when awake, I can sort of see things in my subconscious - it's almost like they're in my peripheral vision. As soon as I concentrate on them, they disappear. The brain is a weird thing.