Extracted from Visual Cues And Parkinson's Disease” By Thomas J. Reiss D.P.M.
The inability to process low speed changes in velocity will impact most prevalently on the motion of objects which are furthest away from the peripheral or central vision of the observer. This is because the virtual motion of objects (rate of expansion or rate of peripheral optical flow) varies inversely with their distance from the observer. Peripherally placed blue filters has a myopic effect, reducing depth of field. What little peripheral data remains is obscured by making the world monochromatic. The net result is the elimination or significant reduction of data for peripheral processing. The effect is to filter out most of the peripheral data which was providing erroneous visual feedback, but it has not been replaced with normal sensory feedback and of greater significance is the fact that simultaneous task performance remains compromised. Clinically this means that suppression of dyskinesia can occur with blue filters because the brain no longer has to try and generate ambulation consistent with irrational visual information but it requires conscious attention and breaks down if the subject must contend with competing stimuli. In addition blue filters also seem to impact the autonomic nervous system... ...There is much anecdotal and some published data to support this".