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Dear Dennis, I respectfully disagree with your suggestion that I define such popular terms as "off" and "on" in such a manner so as to be consistent with "popular usage". Definitions must be objective and quantifiable in order= =3D to be useful as building blocks for other truths. When you use phrases like "when PD symptoms predominate" you enter into the realm of subjectiv= =3D e interpretation - one person's "predominate" is another person's "inconsequential presence". On another subject you raised, visual cues do in fact impact on the quality of movement. One of the optimistic observations for me has been that in PD motor function is not irretrievably lost (as for example in Stroke) but rather is merely inaccessible. There are in fact alternative= =3D ways of accessing these undamaged motor programs. And I still maintain that walking without arm swing (example, with arms behind one's back will not exacerbate festination. Festination occurs wh= =3D en one resists an environmentally induced force of acceleration and there ar= =3D e only short stride length strides available. Examples of environmentally induced forces of acceleration would be a sudden steep descent, or the presence of an obstacle to manuever around or carrying a heavy object. A= =3D ll of these examples cause our center of gravity to be displaced beyond the fall point. This is no problem for the normal person who merely lengthen= =3D s his stride to neutralize the force. But in PD a short stride length requires many short stride length steps in a short amount of time in orde= =3D r to catch up to one's center of gravity and the result is festination. A fall occurs when one fails to catch up to one's center of gravity. Finally walking with hands "stretched out in front" is a means to demonstrate how head tracking can overcome freezing. When we walk the natural interface between body and environment is the feet - but apparent= =3D motion is seen to repeatably stop and go when seeing the feet. This is because apparent motion can only be "seen" when the feet are in the swin= =3D g phase of gait and the apparent motion of the floor appears to pass under foot. In PD I would speculate that there is a problem processing low velocity apparent motion or changes in the velocity of apparent motion. =3D= This is why so many of us can run but cannot walk (running accelerartes apparent motion). Head tracking (walking with arms outstretched and looking at one's fingernails is way of removing the stop start of apparen= =3D t motion seen while looking at the feet. This is because an outstretched a= =3D rm moves with the head - smoothly and continuously. Conversely, a swinging arm is very much like the foot stopping and starting as it reverses direction. This is indeed a difficult forum to discuss such complex ideas. I only ask that you make sure you understand my point of view before you critiqu= =3D e it. Regards, Tom