Monday, October 5, 2009

discussion about pole placement in the coures

Bonnie responded to my last post via email, so I am pasting that  here, along with responses from Dona, Gene and Zach.  I want to make sure that our discussion is captured in the blog so that we end up with a nice record of our process.  The question of sagging has been taken care of by adding a second cable above the one holding the lights. think suspension bridge.  the upper cable takes the shape of the catenary, and the lower cable, the one holding the lights, is perfectly flat. 

(In physics and geometry, the catenary is the theoretical shape a hanging chain or cable will assume when supported at its ends and acted on only by its own weight. Its surface of revolution, the catenoid, is a minimal surface and will be the shape of a soap film bounded by two circles. The curve is the graph of the hyperbolic cosine function, which has a U-like shape, similar in appearance to a parabola.)  Click here for more information about the catenary.

Hi Steve,
I am just now reading the blogs about the overhead string of LED lights and the belt mounted Wii remote. Sorry it took me so long. As others have commented, getting rid of the path off the floor seems like a big improvement. I like the idea of the Wii remote being in the center of the user's back as it won't interfere with cane usage.  It sounds like you will be able to get more accurate feedback about cane arc with the overhead system.
Have you been able to set up the cable and poles and try it out yet? I'm curious about the length of a path, considering that sagging may lead to inaccurate measurements.  If you can't get anywhere near the 30 feet length, would you envision two strings of lights with 4 poles in order to cover the entire 30 foot path? 
Gene & Dona, what do you think would be the impact of having a pole in the path of travel and at the end of the path? Do you think any of the subjects would be able to use echolocation to hear the poles? I'm wondering if the poles could be used as cues for alignment in a way that might interfere with the veering data, which was designed to have no audible markers, so to speak. I read that the pole will be padded, which is good because I imagine some of the younger subjects or those who are not covering their body width bumping into a pole. Do you bumping into a pole would result in the person altering their gait or cane width as a response to contacting a pole? This is the real world. When my students bump into something because they were not covering the entire width of their body (or not paying attention, or cane hand not extended), they often will respond by swinging their cane wider. Some students will slow down because they are now aware there is an obstacle and they want to avoid contacting it. A slower speed and having to move around the pole could affect the subject's straight line of travel.
I'm trying to view this pole idea as a positive learning experience from an O&M perspective. If it is the best way to collect the data (cheaper, appartus readily available, easy to ship/assemble) then there just needs to be consideration of how the pole(s) might alter the subject's cane usage. There are obstacles in the environment so maybe the experimental design is now revised to include an obstacle. If it works out that we only need a pole at the beginning and end of the path, they my points may  not be relevant. I'm simply thinking aloud as to how a pole IN the path might alter the subject's cane usage and alignment.

From Dona:

Wow, Bonnie, interesting points!  I hadn't thought about the possibility of the goal pole serving as an aid to aim for, or the effect of having an obstacle in the line of travel.  perhaps two things could be done to mitigate that:

1. Surrounding the pole with spongy cushiony material should make the echolocation very difficult (even with clicking );

2. Having a line run perpendicular to line of travel a few feet short of the pole will warn the user that he's reached the end.

-- Dona

From Gene


Subjects' vision and hearing are occluded.

A pole in the center of the course would not work. I believe that the 32 foot course will have a single suspended string of lights. The poles are anchored at the top and bottom.

The single forward pole at the end of the course should not interfere at all. It will be padded, of course, and subjects may encounter it when the course is completed.

Does that all make sense.

From Zach:

I was also skeptical about keeping the line taut but I've seen it at
Steven's office and it looks great.

The starting pole will have a wood block or similar on the pole or on
the floor to help subjects square off.  Both poles are wrapped in foam
to prevent injury.
From Bonnie:
Gene - I obviously forgot about the subject's hearing being occluded. That sure eliminates my concern about echolocation. Yes, your comments make sense. I had thought they couldn't string the lights for the entire distance, hence a pole in the middle of the path would be needed. So my concern no longer apply!

Zach - I am glad that the line can be kept taut for the entire distance. This eliminates the pole in the middle. I'm excited that Steve has set it up and it works.

Dona - I like the idea of a textural change in the floor a few steps before the end of the path to let folks know they have reached the end and the pole is near.


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