I agree. The farthest point was badly worded. I was thinking not of a point a long way off, but where the road becomes obscured by the cliff face, which has nothing to do with the actual speed of the car.
In 2017 I wrote about my perception of keeping a car in its lane. I repeat here a portion that applies to slowing on curves, as well as to why we hug the inside of curves.
On a straightaway, I am controlling my line of motion relative to the road margins a considerable distance ahead. Visual features seem to approach relatively slowly at that distance, and I have plenty of time to correct deviations. I remember that when I was learning to drive, I controlled distance between the edges of the car and points much closer to the car on the edges of the road. At that distance, visual features seem to approach quite fast. [I remember that this felt disconcertingly close to the margins of control, and I remember oversteering back and forth.] On a curve to the left I am constrained to see visual features which are much closer than those that I control on a straightaway. I have less leisure to correct deviations, and subjectively I feel less securely in control.
Conversely, when I go around a curve to the right, the center line on the outside of the curve is comparatively much more visible than the right edge was in the above case, because I’m sitting on the left side of the car. I tend to hug the inside of that curve too, but not so closely as I hug the inside of a left-hand curve.
You may suppose that people ‘cut corners’ because it’s shorter and faster. Behavior is not significantly different when the driver is going slowly to e.g. an appointment that he dreads, and therefore is not controlling “get there faster”.
There is a reason that roads are equipped with a center line that divides the two lanes. It sets a boundary. Oncoming cars belong on the other side of that boundary, and I belong on this side. Now imagine that you are driving in a country where there is no dividing line. Instead, there is a center line in each lane. Your task as a driver is to keep your car centered on that line, and oncoming cars are to do the same. Between you and oncoming traffic, with a combined speed over 100 mph, is unmarked blacktop. Are you comfortable with that? I’m not. I want that boundary.
I think these anecdotes support my perception that we control avoidance of lane margins in the same way that we control avoidance of obstacles, and that the appearance of ‘car in center of lane’ (true only on a straightaway, mind you) is a consequence of that.
I think this is why the pheromone trails followed by ants straighten over time. The ants sense the pheromone ahead of them, not under them, and so they head straight for a point ahead of them along the curve, ‘hugging the inside of the curve’ until with some nth ant there is no curve left.
If it’s found that cars do slow down through curves it has nothing to do with the apparent slowing through curves that is seen when people draw curved lines (the “power law” situation). In the car example the curve through which the driver is driving is independent of the actions that are producing the speed of he car. Therefore, the curvature of the road is possibly a disturbance to a controlled variable (possibly centrifugal force) that is being protected from the effects of that disturbance by variations in the speed of the car.
In the power law situation, the actions that produce the curvature of movement are NOT independent of the actions that are simultaneously producing the speed of that movement. So any relationship between curvature and speed that is observed when a person makes curved movements cannot possibly represent the actions (variations in speed) taken to protect a controlled variable from the disturbance of curvature; you can’t compensate for a disturbance with actions that are simultaneously producing that disturbance.
Basic PCT: A disturbance to a controlled variable must be a variable that is independent of the outputs that have an effect on the variable being controlled by a control system: the controlled variable.
Rick,
If that “Basic PCT” is true, then internal conflicts should be impossible, shouldn’t they? Of course the disturbance of one single control unit must be independent from its output but usually one controlled variable is controlled by multiple units and then the output of one unit can cause a disturbance to another unit. For example you are controlling for quick and safe or quick and accurate elliptical movement. Then turning or steering unit can cause disturbance to safety unit which cancels it by lowering the reference of speed unit. Possible?
Eetu
| rsmarken
October 8 |
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bnhpct:
In 2017 I wrote about my perception of keeping a car in its lane. I repeat here a portion that applies to slowing on curves, as well as to why we hug the inside of curves.
bnhpct:If it’s found that cars do slow down through curves it has nothing to do with the apparent slowing through curves that is seen when people draw curved lines (the “power law” situation). In the car example the curve through which the driver is driving is independent of the actions that are producing the speed of he car. Therefore, the curvature of the road is possibly a disturbance to a controlled variable (possibly centrifugal force) that is being protected from the effects of that disturbance by variations in the speed of the car.
In the power law situation, the actions that produce the curvature of movement are NOT independent of the actions that are simultaneously producing the speed of that movement. So any relationship between curvature and speed that is observed when a person makes curved movements cannot possibly represent the actions (variations in speed) taken to protect a controlled variable from the disturbance of curvature; you can’t compensate for a disturbance with actions that are simultaneously producing that disturbance.
Basic PCT: A disturbance to a controlled variable must be a variable that is independent of the outputs that have an effect on the variable being controlled by a control system: the controlled variable.
I deleted my original reply to this because it was wrong. My “Basic PCT” tenet is wrong but not in the way I thought. I had stated the Basic Tenet thus:
A disturbance to a controlled variable must be a variable that is independent of the outputs that have an effect on the variable being controlled by a control system: the controlled variable.
A much clearer (and more correct) way to state the Basic tenet is thus:
A disturbance is a variable whose effect on a controlled variable (CV) is independent of the effect of the control system’s output on the CV.
In situations where the source of the disturbance to a CV is another control system, there will be no conflict if the two control systems are controlling different CVs. This is the situation in my [fly ball catching model (Baseball Catch). In that model, the fielder controls two CVs simultaneously; vertical optical velocity (VOV) and horizontal optical displacement (HOD) of the ball. The forward and back movements that are used to control VOV are a disturbance to HOD and the lateral movements that are used to control HOD are a disturbance to VOV. But there is no conflict because the systems are controlling two different CVs (VOV and HOD).
A conflict exists when the outputs of two (or more) control systems are involved in control of the same CV. For example, the two control systems may be controlling for your location relative to two different reference specifications; one system may want you to stay home writing a book while the other wants you to be out getting exercise. So one system is producing outputs that would prevent you from moving; these outputs are a disturbance to the location CV being controlled at “go out and exercise”. The other system is producing outputs that would get you to the gym; these outputs are a disturbance to the location CV being controlled at “stay at your desk”. They are disturbances per the revised definition above because both have an effect on a controlled variable (CV) that is independent of the effect of output of the other system that happens to be controlling the same CV. In this case, each system will act to prevent the disturbance produced by the other from having an effect on the CV – moving it from the reference state. The result is that each system acts to prevent the other system from getting the CV to the reference state specified by that system.
My demo that I call the cost of conflict was an attempt to demonstrate the cost, in terms of loss of control, of an internal conflict, like the one described above. But since people won’t remain in internal conflict for more than a couple seconds (this can be shown with Powers’ “portable demonstration” of internal conflict) I create a conflict that results from taking away a degree of freedom from the mouse controller. So the loss of control is created by environmental rather than psychological means. But I think it’s a reasonable demonstration of the stress created by persistent internal conflict.