Cognitive accessibility is the area where usability bumps into disability. I consider cognitive ability to be a bell curve. With most people falling in the same area, but at one time or another I think everyone will experience the world from a perspective somewhere towards the edge of that curve. For me, its because I am autistic. For others, its because they are tired, or in a rush, or an older user. For many, they happen to be drunk. With this in mind, I propose that cognitive accessibility at the end of the day is really just usability at the extremes. We will all experience it.