The cognitive revolution arose out of the Turing (and then Chomsky, and others)-inspired notion that the mind is a computing machine. Since computers generally don't have sensory modalities, as we traditionally conceive them at least, and they don't really need them, their representations tended to be digital, and thus amodal. Since cognitive scientists were treating minds as computers, it was natural to make their representations digital, and amodal, as well. And since the 1950s, that has been the orthodox view of cognitive scientists: representations are discrete information states that can be subjected to syntactical processes, just like the machine language of a computer. Sure, there have been some dissenters, like the cognitive linguists and dynamic systems theorists, but they have existed on the fringe of cognitive science for the most part, being either silly (cognitive linguists) or near incoherent (system theorists)1. A few years ago, though, Larry Barsalou and some of his colleagues (see e.g., this book) began to argue that it was time to leave our amodal, disembodied representations behind, and return to 17th century empiricism. To do this, we have to return to the belief that cognition is "inherently perceptual," i.e., that representations are inherently tied to sensory modalities. Thus, perceptual symbol systems theory was born.
Now, there are lots of problems with perceptual symbol systems theory (PSS), though I won't get into most of them (see here for a thorough critique). The most general criticism is that, ultimately, PPS doesn't make any predictions that theories utilizing amodal representations couldn't handle. This makes it difficult, empirically, to decide between the two alternatives. More specific criticisms include the fact that PPS theorists always end up positing a whole bunch of amodal (sometimes they call them multi-modal, just to avoid admitting that they're amodal) mediating representations to get their theories to work. They also have a hell of a time with some of empiricism's old archenemies, like abstract concepts (though not for lack of effort; see here) and arbitrary signs (like words). All-in-all, though, PPS has been good for cognitive science. It has forced us, especially those of us who study concepts, to take perception seriously again.
The way PSS has managed to get concept researchers to take perception seriously is by inspiring research that those of us who are firmly entrenched in the amodalist world-view would never have thought of, producing findings that would likely have otherwise gone undiscovered. For example, in one experiment2, participants were given the names of items like "watermelon" and "lawn," and asked to list their properties. Some of these participants received further instructions to picture the items in their heads before listing properties. Furthermore, some of the participants received the normal names, while others received modified names (e.g., "sliced watermelon" or "rolled-up lawn). The predictions Barsalou derived from PSS were twofold: people who pictured the items would produce different lists of features, depending on whether they received the normal or modified names, because the perceptual features would be different (e.g., lawn has green grass, while a rolled-up lawn has roots and grubs and all sorts of other creepy crawlies), a prediction that Barsalou believed amodal systems theories would also make, and also that the people who hadn't received the picture instructions would produce feature listings that were not significantly different from those of the people who did receive them. This second prediction, Barsalou argued, could not be made by amodal systems theories, because it required that these people spontaneously use perceptual simulations of the items to represent them. And it turned out that the two groups did produce the same listings, with watermelons having features like "green," "striped," and "round," and sliced watermelons having features like "red" and "seeds." In an even more fascinating study, Simmons and Barsalou3 asked participants to categorize objects presented in photos. Some participants were told to make hand motions that were compatible with some of the items (e.g., the motion used to turn on a faucet). These participants categorized the items faster than participants who did not perform compatible movements. Simmons and Barsalou argue that this is because the perceptuo-motor actions facilitated the perceptual simulation of the items, resulting in faster categorization.
The results of these PSS-inspired experiments, and others, whether the support PSS over amodal theories or not (again, while they were derived from PSS, they appear to be consistent with amodal theories), have sometimes wide-ranging implications for theories of concepts in general, such as the types of information we represent, how that information is retrieved, and the role of context and imagination. Thus, while the the prospects for PSS as a theory of mental representation, in its current form at least, may not be very good, its contributions to cognitive science in the form of novel hypotheses that lead to theoretically important empirical findings is undeniable.
At this point, you're probably wondering what all of this has to do with intelligent design theories (ID). After all, the title of this post is about ID, not cognitive science or PSS. Well, I think that PSS and ID have some very interesting commonalities, which can allow us to use PSS as an analogy when reasoning about ID. For instance, they're both 17th century ideas (which, in more rudimentary forms, go back even further) that are being revived in order to challenge more recently developed scientific orthodoxies; the adherents of both claim to be inspired by empirical data that they believe their more entrenched alternatives cannot handle; and they're both ultimately likely to fail as scientific theories due, among other things, to their ultimate inability to empirically distinguish themselves from their alternatives.
Once we align the two theories so that these attributes are in correspondence, we can then begin to look at their differences in informative ways. In particular, we can try to understand one key difference: PSS has led to novel hypotheses, which have produced interesting experimental results that have advanced our knowledge of concepts and mental representation, while ID has yet to produce any hypotheses that have led to experimental results of any kind. It might be objected that ID concepts like Behe's "irreducible complexity" have led to research demonstrating that certain biological mechanisms are, in fact, producible through natural selection, but since biologists were already aware that the evolution of these mechanisms was, as of yet, unexplained, it's hard to argue that ID had anything to do with this research, other than adding another sentence or two to the discussion sections in the papers describing it.
What other difference might explain this big one? The answer is obvious. PSS theorizes that concept representations are produced and processed as simulations within the same perceptual systems of the brain that represent and process non-conceptual information from the senses. Thus, we can use our knowledge of those perceptual systems, theorized properties of the simulation process, to make predictions about concepts. ID has nothing analogous to this feature of PSS that would allow it to make predictions. In place of such a feature, ID has an intelligent being of a "mysterious and incomprehensible nature," about which the natural phenomena that we are trying to explain can tell us nothing. Because we know nothing about this being's nature, we have nothing to work with when it comes to making novel predictions. Thus, we're left with a theory that can add nothing to science, because it gives us no new positive knowledge. At most, it can merely trumpet the null hypotheses of its alternatives.
So, PSS serves as a good example of the sort of theory that ID could be, but isn't, and unless it makes some positive statements about the nature of the designer that go beyond attributing the vague property of intelligence to it, never will be. If the adherents of ID were actual scientists, this is the problem they would be working on. Merely attempting to show that there are cases which evolutionary theory cannot yet handle isn't going to cut it. Since ID provides nothing in the way of positive alternative explanations, the best way to deal with the fact that evolution has not yet explained everything is to note that evolution is still the only potential explanation. If the adherents of ID were real scientists who were genuinely interested in the scientific process, they would be working very hard to come up with empirically testable theories concerning the nature of the designer. Short of that, they've got nothing.
1 I purposefuly leave out connectionism, because while connectionist representations can be ostensibly analog, and even considered modal (depending on the model), when you strip away the surface-level representations of the models themselves, what you have is a multi-dimensional space with points and vectors serving as representations, and that seems pretty damn digital, or at least amodal, to me.
2 Barsalou, L.W., Solomon, K.O., & Wu, L.L. (1999). Perceptual simulation in conceptual tasks. In M.K. Hiraga, C. Sinha, & S. Wilcox (Eds.), Cultural, typological, and psychological perspectives in cognitive linguistics: The proceedings of the 4th conference of the International Cognitive Linguistics Association, Vol. 3 (209-228). Amsterdam: John Benjamins.
3 See here, p. 11.
4 It might be objected that ID concepts like Behe's "irreducible complexity" have inspired research demonstrating that complex biological mechanisms can, in fact, evolve through natural selection, but biologists were already well aware that there were some mechanisms for which they did not have an evolutionary mechanism, and thus needed to study more thoroughly. Thus, it doesn't appear that "irreducible complexity" has actually inspired any research, and it certainly hasn't produced any novel hypotheses, but has instead built a case around the null hypothesis that scientists would have worked with anyway.