The Book Feed

Question: 

How do people visualize when reading?

My Experience:

I remember reading when I was little and I would create settings, scenes, and characters with relative ease. Yet, now I find my visualization lacking. Although, it could be because I'm over thinking it. For example, when I'm reading, most of the characters/scenes/settings are hazy. Sometimes, I feel like I need to stop and actively create a crisp image, to then become frustrated, because the process is supposed to be passive (right?). However, once I've finished reading, I can play back what I've read without a hitch.  Could it be that I'm too conscious when reading? By too conscious, I mean that I'm overly aware of trying to visualize and thus interrupting the passive ability. For now I'm convinced that my method of visualization is collecting data as I read the book and letting it "sink in". If this is true, it still explains why I can remember characters from years ago, just not when they became crisp in detail. 

What's your experience with visualization?