Hello, all --
After several days of on-and-off thinking about affordances, I think I see a few new facets of the problem. What seems to have been building up in my head is the idea that affordances -- and actually feedback functions in general -- are controlled variables.
This control is done at some lower level, a level in which the output function is reorganized to use different lower-level systems, or selects them (by sending reference signals to them) in some systematic way.
This doesn't necessarily mean that we actually change the affordances of specific items. It can mean that we select items according the results we intend to produce by using those items. The selection process determines which affordance we actually use.
This implies that the "standardization" of artifacts like tools is not necessarily what we need. We need a variety of possible means of control, from which we can select according to the specific purpose we want to carry out. A relatively small number of people actually produce new items or change old ones, but if they don't use the result themselves, they create them for the purpose of giving others new choices of means (e. g., so the designers can sell them). It is still the purposes of the user that determine which feedback function or affordance will be used to satisfy any given set of purposes.
And a selection is needed because not everyone can use a given affordance -- I have a friend who, for target practice, selects a bow with a 120-pound pull just to get a flat trajectory, a bow that I can scarcely bend, much less use to shoot an arrow.
It seems clearer to me now that the whole idea of a fixed feedback function or affordance is a mistake. It's really the "behavioral illusion" in another disguise. It seems that the affordance in the existing feedback path is what controls behavior, but in fact the affordance itself is controlled (by selecting one for use) as a way of achieving an end that has already been specified. The actual behavior involved relates to the purpose in the usual way, being adjusted according to the error and acting through the selected feedback path to make some perception match a reference setting. The choice of feedback path or affordance is varied until the specified goal is achieved.
This choice process is simply one of the usual ways a lower-order control system is used to produce an input needed by a higher-order system. The feedback path that the higher system sees includes all the lower-order control systems involved.
Best,
Bill