[From Bill Powers (2008.11.26.0713 MST)]
This does look like a good candidate for a model, though perhaps a rather complex one for the first attempt.
One interesting feature not mentioned is that to make the money economy work, it's necessary to be sure that the items being purchased are not freely available without paying for them. The money then acts something like a schedule of reinforcement, in that the money, like the Skinnerian lever, is the only environmental feedback function available through which behavior can control the input of whatever is wanted. When control is perfect, the rate of spending money is determined by the reference level set for input rate and the price per unit input.
An interesting feature of this arrangement is that if the price is increased, it's necessary to spend more money to get the same amount of the good. If the good is a necessity (as when the only way to get air is to buy it), this will surely happen if the organism remains alive.
In the case where the input item (marshmallows) is apparently wanted in unlimited quantities, it would seem that no amount of the input up to the observed maximum is enough to match the reference level. Either that, or there is something in the marshmallows that is wanted in normal amounts, but which is present only in trace amounts. When I was young I had a dog named Skipper, who could be induced to drink endless quantities of water just by filling his bowl with water and then adding a tablespoon of milk to it. Without the milk, he would drink normal amounts of water, but milk (or the idea of milk) was apparently very valuable, so even just a tint of milk in the water indicated presence of the ambrosia. However, it was very difficult to satisfy the reference level for milk when all that was present was a homeopathic dose of it. This is similar to Skinner's demonstration that pigeons given ever-decreasing amounts of reinforcer per peck on a key would wear their beaks down to stubs trying to get enough to eat (Skinner seemed to have no gene for empathy).
Hmm. Does this have something to do with obesity? Do we overeat because we're trying to get something from food that has been replaced by a cheaper substitute that tastes the same (or better) but doesn't have the same effect inside us?
I think we could show, with a model, various ways to create the appearance of unlimited appetites without any such thing actually existing. I'm pretty sure the explanation offered by this article is incorrect:
"That's because economics is in essence the study of incentives, and how people -- perhaps even monkeys -- respond to those incentives. "
I would say that economics is the study of people (or monkeys in laboratories) getting what they want or need for themselves when the means of doing so is money and other means are unavailable or are strongly discouraged.