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Brian, A few final comments on this topic and then let's give the readers a rest. You said: "For example in the long list of activities you mentioned as dyskinesia suppressants all bar looking through a zoom lens require movement. So in each case two things are happening - optical flow is being accelerated and the subject is involved in physical activity. Whilst it is possible that any decrease in dyskinesia is the result of changes in the rate of optical flow it is also possible that it results from the activity. Lending support to this possibility is your statement that the activity with the greatest rate of optical flow, but least physical activity, riding in a car, has no effect on dyskinesia. I assume, as you are about to publish a paper on the subject that you have addressed and resolved this question. Would it be possible to give us an idea as to how you eliminated that possibility." There is a reason why riding in a car does not suppress dyskinesia and riding on a motorcycle or bike does. And that is, that in order to suppress dyskinesia,the optical flow that one percieves has to be interpreted by the brain as apparent motion i.e. motion that is a consequence of the observer's eyes moving to a new vantage point as opposed to real motion i,e motion which occurs independent of the observer's activity. The former gives feedback of the observer's motion the latter does not. In order for optical flow to be interpreted as apparent motion it must behave in a manner which conditioning (experience) has taught us is consistent with the observer's t activity and it must occupy all of (or an overwhelming majority of ) the visual field. When only a portion of the visual field moves it is interpreted by the brain as real motion. The motion one sees through the window of a moving car is referenced to non-movinig visual data i.e. the window frames, the hood of the car etc. and so is interpreted as real motion. Riding on a bike or sitting in a ski chair lift has no such reference points - the entire visual field appears to move and so is interpreted as being apparent motion and a reflection of self-motion. And one more point: While discovering the underlying cause of dyskinesia, akinesia or freezing is certainly an important goal my primary objective (being a PWP) is to find a way to "ease the burden". So it is of greater importance from my point of view to find the parameters which can infiuence and impact on the symptom in the hope of exploiting these forces in some kind of therapeutic device. The former objective is clearly beyond my ability and training while the second may not be. regards, Tom