It looks like TSRM think that sharks find food by detecting the electrical fields of fish, but here is what Andrew says they say:In the niche of the shark 'an edible thing' and 'electric field of, say, type F' are nomically related. To predicate of the shark (a) 'detects electric field of type F' and (b) 'takes to be an edible thing' is not to refer to two different states of affairs, one (viz. (b)) that is reached from the other (viz. (a)) by an inference. (Turvey, Shaw, Reed, and Mace, 1981).
Here, it looks like Andrew is saying that TSRM think that sharks can't find food (an affordance, right?) by detecting an electric field (a "unit" of physics). [Actually, this passage seems equivocal to me. There's the part in the first sentence about Gibson not denying that information is rooted in physics.]Turvey, Shaw, Reed & Mace (1981)But Gibson is not denying that information is rooted in physics; he's simply pointing out that the correct level of analysis for the information available to a perceiving organism is ecological. What an organism needs to know is not how far away something is, but whether it can reach that thing - in other words, affordances. You can't get to affordances via the objects of physics, because affordances are personal and contain meaning while physics is neither of these. You therefore have to get to affordances by detecting information about affordances, not units of physics. (italics added, ref here.)
But, then, Andrew also writes this (ref here),
Now, one must relate organisms to the physics.Enter Turvey, Shaw, Reed and Mace. Their reply to F&P is simple: Gibsonian information is suitably constrained (i.e. you can’t just claim any old property can be perceived) and that these constraints are not simply ad hoc, but rooted firmly in a consideration of the physics of the world in which vision evolved. This paper is elegant and clear; in fact its elegance and clarity manage to retrospectively make F&P’s paper worthwhile because it caused Turvey et al to write this.The constraints lie in the existence of ecological laws. A law describes a set of conditions and the necessary consequence of those conditions (if the temperature of pure water at sea level is 100°C then the water will boil). Laws have scope: the scope is laid out in the set of conditions. Within that scope, the conclusion is necessary, i.e. if the conditions obtain and the scope is correct the conclusion must be the case. Ecological laws lay out the conditions and consequences by which a pattern in (for example) an optic array can specify an object or event in the world; these conditions must relate to the physics of the situation (so ‘shoeness’ is not the kind of property we are dealing with).(italics added)
So, it looks like there a real dilemma here. On the one hand, Andrew wants physics ontology to be incommensurable with perceptual ontology, perhaps so that psychology is apparently not reducible to physics. On the other hand, Andrew wants physics to be commensurable with psychology, so that he can resist the Fodor and Pylyhshyn "trivialization argument". This seems to me not a mere slip in wording, but the product of distinct theoretical demands. There are two things, neither of which an EPist, like Andrew, seems to want to abandon.
Personally, I would think the thing to do is abandon the incommensurability thing. But, of course, the really big thing to do would be to give up on EP.