Some people with some forms of (what are labelled) 'mental health conditions' protest that it's not a deficiency at all - just a different way of being. Certainly it's easy to sympathise with this for conditions such as high-functioning Asperger's, ADHD and even some manifestations of bi-polar. (Stephen Fry famously said that he wouldn't change this aspect of himself even if he could).
"As Jaynes saw it, a great deal of what is happening to you right now does not seem to be part of your consciousness until your attention is drawn to it. Could you feel the chair pressing against your back a moment ago? Or do you only feel it now, now that you have asked yourself that question?"
A year or two ago i ran into an article that looked at autism/aspegers as "intense world" syndrome. This in that people with it do no shut out inputs that "neurotypicals" do by reflex.
I think for someone with that the idea of not being aware of the chair is borderline preposterous. It may only be valid when "in the zone", fully engaged and focused on some task, be it programming, gaming, or perhaps a good book.
I don't see how your your brain censoring unnecessary sensory information is preposterous. But once its drawn to your attention - it can be hard to stop thinking about it and get it "filtered" again.
If you believe that attribution of consciousness to only yourself is a culturally developed feature (which seems plausible given the existence of many mystics who don't seem to do so) then it is very possible that in some people the machinery that is required to do so doesn't work properly resulting in varying degrees of schizophrenia.