Well, it turns out that the "illusory mindspace into which we project and observe the images we conjure" differs in all of us, as a very timely article in the New York Times indicates:
That supports my conjecture that our mental images are just (re)activations of various nerve networks in our brains. They are ones normally invoked by our visual, auditory, and other sensations, but we are also capable of invoking them in the absence of those perceptual sensations.
