It is interesting to think about the evolutionary implications of the development of a center in the brain that monitors and contrasts sensory input with the corollary discharge signals. That we have developed this center and that we are still affected by itin the cases of motion sickness, jet lag, and phantom limb syndrome, for examplesuggests that it is a part of the human experience to have a view of "reality" that differs from the reality of "reality". Put in more comprehensible terms, it seems that humans, as a species, have found it adaptive to maintain a system to check our perception of the outside world. This would suggest that our perceptions, our internal reflection of our world, tends to vary with the original input. The higher levels of processing may therefore interpret original sensory input to a degree that its reflection of the input is weakened. The system of checking the outside input with our internal reflection of this input also suggests the need to maintain a feel for the outside inputthat our tendency to stray from the original outside input and to create internal models that stray further and further from the original idea is selected against. It is to say that it is beneficial if not necessary to keep in touch with the "outside world" and it is not possible to function at our best while living in a world that exists entirely within our heads without regard to the external input that bombards us constantly. This argues against the idea that we exist as figments of our own imaginationsthat the world is because we think it is. That we feel ill at ease when we our internal perceptions stray from the input received more directly from the external world suggests that there is an external world from which to stray. Perhaps there is an external reality after all.
Yes, indeed. Or at least you've given the best evidence for it that I know. I don't think though that the necessity for checking is because our perceptions tend to "vary with the original input". An alternate possibility is that the internal model is more fundamental, and that we simply use input to check/update it. Possible? Anyhow, nice thinking through of interesting problem. PG