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Tom Riess, Thank you for your comments. I have heard of your success with virtual reality devices in dealing with the problem of freezing. I have yet to experience freezing. As I understand it the VR device you have created projects a grid over the visual field, thereby supplying additional visual cues. Do you have a theory as to why the additional cues work? The problem you address in your work has to do with moving through the world with eyes open, and the question I was addressing is why balance is worse when the eyes are closed. I wonder though whether we are talking about two aspects of the same problem, even if overtly they seem different. You mentioned two categories of vision: > One is seeing in the ordinary sense, the other is unconscious > visual processing of information. The latter is similar to the > visual processing that occurs while on a ship at sea or in a > moving car. We are not conscious of this type of vision but it can > impact on our motor performance for example motion sickness. We > monitor the apparent motion of the environment as we walk through > it with this type of vision. Perception is a strange thing when I think about it. Things appear to us as if we experience them directly, but this is not the case. The receptor cells in the various sense organs are stimulated by light, heat, sound, etc., energy, and they in turn transmit electro-chemical impulses along nerve pathways leading to the perceptual areas of the brain. There the impulses are interpreted and integrated, and, voila, something we regard to be a single, common outside world "appears" to us, except it's a constructed representation residing in each of our heads. By the two categories of vision do you have in mind the common sense experience of seeing vs. the process of the mind in creating the unified visual/aural/tactile etc. representation? I'd like to explore this a bit further, although I'm getting out of my depth. It's been a while since I read anything about perception, and my old books on this subject must be out of date. Phil Tompkins