[From Rick Marken (2016.02.14.1250)]
Bruce Abbott (2016.02.14.0945 EST)--
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Rick Marken (2016.02.13.1140) --
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RM: So I have developed a demonstration of two levels of control operating simultaneously in a tracking task. The demo still needs some work but I'm so excited about it I would like people to give it a try and let me know if it works for them. An initial version of the demo is up at:Â
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<Two Level Control; www.mindreadings.com/TwoLevelControl.html
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RM: Any comments or suggestions on this demo would be greatly appreciated.Â
 BA: I tried the demo and have a few comments/suggestions:
RM: Super, thanks!Â
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1.     The instruction “Press the “Basic Tracking Experiment" button below to open the window that runs the tracking taskâ€? is unnecessary – theree is no such button and the screen is already as if you had pressed such a button.
RM: Yes, that's a remnant of an obsolete demo. I'll fix it. Â
2.     There may be differences in speed of execution of the demo depending on what computer one is using. I found the cursor movements generally too fast to track with any degree of accuracy – well below the level of accurracy shown in the top graph from your own run. If fact, sometimes the cursor would just disappear from one location and reappear in another. It would be nice to know whether anyone else experiences this problem and, whether or not it occurs, what computer they were using. Mine is an older HP laptop running the Windows Vista operating system. (Come to think of it, the system I use to control the mouse is something of an antique as well!)
RM: It works well for me on my new PC, Old PC, iMac and iPhone (using touch screen rather than mouse). Those are all pretty new (and fast) systems. The system could have a big effect because I am calculating the velocity of the mouse on each animation iteration and it's that velocity that I am disturbing via multiplication. And I get the resulting mouse position by integrating the the velocity. There is a lot of room for noise being introduced there and without good temporal resolution of the changes in mouse position things could get ugly. It would be nice if others could try it and describe their experiences on their computer. >
3.     It’s hard to tell, but perhaps the above problem is due to the effect of the “force� on the cursor. If the cursor suddenly accelerates it may reach a high rate before the participant has time to even begin to compensate for the change. In other words, the force disturbance may be causing effects that are outside the bandwidth for effective control.
RM: Yes, it's something like that. I have trouble tracking well myself. I have tried changing the force disturbance and the one that's being used gives the best results for me. I can try tweeking it some more once I get some more reports from others. >
4.     I don’t experience the disturbance as a force acting on the mouse, but rather as an acceleration of the cursor. To compensate for it, I of course must vary the force applied to the mouse so as to generate an opposing acceleration of the cursor. A true force disturbance to the mouse would be experienced as a push or pull on the mouse.
RM: True. I think the main thing I want to show is that there are two control processes going on simultaneously and that they are hierarchically related. In order to show this I'll have to see if a two level model behaves as the person does. So that's the next step. >
BA: Â You should be able to implement a true force disturbance by switching from the mouse to one of those joysticks with force feedback.
RM: Yes, but I really like the idea of being able to let people demonstrate this to themselves with just what they have on their laptop, phone or tablet (using mouse or keypad).Â
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BA: What does the block diagram look like for your two-level system?
RM: I'm going to include it in the next iteration of demo once I get the two level model working. That is, if the two level model works like a person; if a one level model does just as well I'll have to abandon the idea (once again) that this is an example of two level control.Â
Thanks again for the comments.
BestÂ
Rick
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Bruce
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Bruce A.
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Richard S. MarkenÂ
Author, with Timothy A. Carey, of  <Amazon.com People: The Paradoxical Nature of Being Human.Â