If I had to describe it, I'd say it's more like an extra set of eyes that is just looking at the thing I'm imagining. It doesn't replace what my physical eyes see.

Note that these eyes need not be static, even when I am. I can easily imagine myself flying through some space, looking out through those eyes, even if I'm in my chair. I can also have them grow a body and interact with the imagined scene in front of me.

While it doesn't replace what I'm seeing in the real world, it takes up some attention - I might not be paying as much attention to things physically in front of me.