That's a great description, Rick! Me too. Last year I had described it (perhaps more Copernicanly) as the floor surprising me, meeting my foot earlier or later than anticipated....a little like walking in a rowboat. Isn't it annoying when the world doesn't conform to one's expectations? As if we don't have enough to process already...LOL.

You probably know that the mechanisms at play here have to do with proprioception. Trying to remember the precise spelling on that word, I just stumbled on two things that may be of interest:

The first is the more detailed than expected entry on proprioception from, believe it or not, Wikipedia. The info isn't as deep as that to which some of us are accustomed, but the scope is fairly wide for an introduction to the topic and contains jumping off places for additional research. See en.wikipedia.org/wiki/Proprioception

The second is really cool. Have you heard of this, Rick? This is from the 2009 International Symposium on Wearable Computers.

Potentials of Enhanced Context Awareness in Wearable Assistants for Parkinson's Disease Patients with the Freezing of Gait Syndrome
Linz - Austria
September 04-September 07
ISBN: 978-0-7695-3779-5
Marc Bächlin et al

DOI Bookmark: http://doi.ieeecomputersociety.org/10.1109/ISWC.2009.14
Freezing of gait (FOG) is a common gait deficit in advanced Parkinson’s disease (PD). It is often a cause of falls, interferes with daily activities and significantly impairs quality of life. Gait deficits in PD patients are often resistant to pharmacologic treatment; therefore effective nonpharmacologic assistance is needed.In this paper we show the potential of context aware assistance for PD patients with FOG and present our first results on start and turn FOG assistance using our modular wearable research platform. We developed a real-time FOG detection system which provides external acoustic cues when FOG is detected from on-body motion sensors, until the subject resumes walking. In an evaluation study, ten PD patients tested our device. We recorded over 8h of data. Eight patients experienced FOG during the study, and 237 FOG events have been identified by physiotherapists in a post video analysis. For the first time PD patients with the FOG syndrome were assisted by a context-aware wearable system. We report a high accuracy of freeze detection (73.1% sensitivity, 81.6% specificity, user independent). Based on subjective reports, the majority of patients indicated a benefit from the automatic cueing.We discuss how additional sensor modalities can paint a more complete view of the user’s context and may increase the system’s accuracy, decrease its latency, and eventually allow going from freeze detection to freeze preemption.