Sharks electrically detect things to eat and things that impede locomotion (Kalmijn, 1974). An edible living thing such as a flatfish differs in ionic com• position from the surrounding water, producing a bioelectric field partially modulated in the rhythm of the living thing's respiratory movements. A flatfish that has buried itself in the sand will be detectable by a shark swimming just above it. Reproducing the bioelectric field of the flatfish artificially, bypassing a current between two electrodes buried in the sand, invites the same predatory behavior. The shark digs tenaciously at the source of the field departing from the site when the act fails to reveal an edible thing (Kalmijn, 1971). Now there is no intelligible sense in which it can be claimed that the source ought to have appeared inedible if the shark's perception were free of error and if the shark's perception of affordances were direct. 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. Rather, it is to make reference in two ways to a single state of affairs of the shark-niche system. The linking of (a) and (b) is not something that goes on in the "mind" of the shark, as the Establishment would have it. The linking of (a) and (b) is in the physics of an ecological world, namely, that system given by the complementation of the shark and its niche.Third, consider TSRM's claim that "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." This, too, seems to me to be overstated. "Detects electric field of type F" and "takes to be an edible thing" have different intentional or semantic contents (maybe both have intentional contents that differ or maybe (a) lacks intentional content, where (b) does not), so doing the detecting and doing that taking are not the same state of affairs in a perfectly pedestrian sense that EPists often admit. This is part and parcel of seeing something as an electric field (which would not seem to be an affordance) versus seeing it as an edible thing (which would seem to be an affordance). In fact, part of the rationale for this shark experiment is to try to disentangle these different intentional objects--these different objects of perception.
Now, maybe there is some sense in which (a) and (b) are the same (which TSRM do not explicate), but there is a crucial sense in which they are different (which I have explicated). This is why I temper my objection, noting that their claim is overstated.