speculations regarding vision

[Tom Riess <74244.1521@xxxxxxxxxxxxxx>]

I too have been most impressed with the number of PWP who report problems
with vision.  It prompted me to ask the following question which went
largely unaswered:  of those of you who have problems of vision, how many
of you also have gait disturbances?  According to my unproven  speculations
I would propose that there are two categories of vision:  one is conscious
seeing which is seeing in the "ordinary" sense i.e. vision filtered 
through the eye of experience.  This is the kind of vision which enables us
 to identify a familiar face or object.  But I would  propose there is  a
second category of vision which I call unconscious vision.  This vision
(primarily peripheral) is used to monitor motion, generally apparent motion
i.e. it monitors motion which only seems to occur and is the result of our
eyes moving from one vantage point to another.  This unconscious vision
only becomes conscious when it is not in compliance with the motor activity
which produced it.  When this is the case an "explanation" is  required to
resolve this conflict. In the absence of an adequate explanation motor
activity stops (e.g. freezing).   Here is a more specific example.  Imagine
yourself driving your car and you are  stopped  at an intersection. 
Suddenly the parked car to your right begins to bac   kup.Sensory
conditioning has taught us that peripheral motion is usually apparent not
real and  signifies movement of ourselves.  This apparent conflict causes 
us to reflexively slam on the brakes (freeze).

The point of  all this is that all the PWP who reported vision problems
naturally  reported problems of conscious vision (e.g. depth perception
changes, double vision).  However, I would suggest that problems of vision
very likely crossover into the realm of unconscious vision.  Since
unconscious vision is a reflection of motor activity and can determine
whether or not such activities are performed as well as the characteristics
of  their performance, this raises the possibility that visual perceptive
or processing pathology could be a cause of gait disturbances in PD.

Regards,
Tom