I encounter many intelligent people (not usually LWers, though) who say that despite our recent scientific advances, human consciousness remains a mystery and currently intractable to science. This is wrong. Empirically distinguishable theories of consciousness have been around for at least 15 years, and the data are beginning to favor some theories over others. For a recent example, see this August 2011 article from Lau & Rosenthal in Trends in Cognitive Sciences, one of my favorite journals. (Review articles, yay!)
Abstract:
Higher-order theories of consciousness argue that conscious awareness crucially depends on higher-order mental representations that represent oneself as being in particular mental states. These theories have featured prominently in recent debates on conscious awareness. We provide new leverage on these debates by reviewing the empirical evidence in support of the higher-order view. We focus on evidence that distinguishes the higher-order view from its alternatives, such as the first-order, global workspace and recurrent visual processing theories. We defend the higher-order view against several major criticisms, such as prefrontal activity reflects attention but not awareness, and prefrontal lesion does not abolish awareness. Although the higher-order approach originated in philosophical discussions, we show that it is testable and has received substantial empirical support.
ETA: I completely forgot that you wrote an article on that, sorry. There were two people in the comments whose comments seemed to suggest that they lack a "mind's eye", Garth and Blueberry.
Note that you are using potentially confusing analogies and therefore terminology here. Some people, e.g. my dad, are unable to see anything with their "mind's eye". Indeed, those people don't even know what you mean by that. If you ask them if they are able to imagine a beautiful sunset then they think that you are asking them if they could describe or paint a sunset (database query), they do not understand that you ask them to simulate a beautiful sunset visually and experience it with their "mind's eye" as if dreaming. My dad can only experience visual images if they actually happen live, but he has visual dreams when asleep. That's how I figured this out in the first place, by asking if he is able to deliberately cause dream-like sensory experiences that do not correlate with the outside world (he can't, it is all "black"). I asked others and there are quite a few people who are not capable of "daydreaming" (my mom is). I don't know how else to call this but a lack of a certain type of consciousness.