But what does it mean "visualize" ? I can "think" of an apple and all it's detail, but I wouldn't describe any visual sensation. If I had to draw the apple I could draw it detail, right down the the variation in colors on it's skin. But no sense of this experience feels like a visual sensation. It feels like "thinking". To me, the act of closing my eyes emphasizes that this isn't a visual sensation for me, because with my eyes closed, I see darkness.