Adams and I have a reply to this, among other things, in a paper, "The Value of Cognitivism in Thinking about Extended Cognition" that should be coming out in about a month.
Having already replied to much of Clark’s rejoinder in defense of coupling-constitution arguments, we here limit ourselves to one argument that we have yet to address. This argument might be thought to vindicate coupling-constitution arguments. This is Clark’s “Hippo-world” thought experiment, which goes something like this. For idiosyncratic historical reasons (perhaps the enduring influence of the philosophical “picture” of one Hippo-Descartes), all neuroscientific attention is focused on the hippocampus. Several decades of research using single cell recording techniques, brain lesions in animals, and so forth has lead to important and replicable findings about the processes that occur within the hippocampus. Scientists on Hippo-world are nothing if not inventive and one day some turn their scientific attention to the rest of the brain, where they too begin to make some significant progress. They discover new neural circuits and processes that are linked to processes within the hippocampus. And among these new scientists, there are some who are so bold as to conjecture that cognitive processes occur within the whole of the brain. Inspired by this new science, some philosophers, Hippo-Clark and Hippo-Chalmers, among countless others, openly disavow the remnants of the traditional Hippo-Cartesian view of the mind and declare that “Cognitive processes ain’t (all) in the hippocampus!”
Yet, there are philosophers who resist the enthusiastic philosophical interpretations of the studies of the entire brain. Some philosophers, such as Hippo-Adams and Hippo-Aizawa, conjecture that, in its studies of the hippocampus, science has discovered the scientific essence of cognition itself. More boldly, these philosophers conjecture that what occurs within the hippocampus is cognitive, where what occurs within the other regions of the brain is of a distinct non-cognitive character. These philosophers maintain that genuinely cognitive processes, processes bearing the mark of the cognitive, take place within the hippocampus, where other supportive non-cognitive processes take place within the other regions of the brain.
In reflecting upon Hippo-world, Clark wants his reader to have the impression that the critics of whole brain cognition of the Hippo-A-Team variety have an overly narrow vision of what cognition is. Like Adams and Aizawa of earthly fame, Hippo-Adams and Hippo-Aizawa display an overly restricted conception of cognition. In Hippo-World there are extra-hippocampal processes that complement those of the hippocampus and that are integrated with hippocampal processes to augment the power and scope of human intelligence. Similarly, on earth, there are bodily and environmental processes that complement those of the brain and that are integrated with brain processes to augment the power and scope of human intelligence. Hippo-Adams and Hippo-Aizawa should accept extra-hippocampal brain processes as genuinely cognitive processes, just as Adams and Aizawa should accept environmental processes as genuinely cognitive.
Unfortunately for Clark, such prima facie plausibility as the Hippo-World argument might enjoy evaporates on more careful examination. The Hippo-World account relies upon a kind of philosophical misdirection. In describing the case, Clark provides the usual extended cognition sorts of observations of the causal roles played by the surrounding structures and the interplay between them. He observes the coupling of the hippocampus and the extra-hippocampal brain and the way in which the whole can do more than the isolated parts. And in this case, one is inclined to think that the whole of the brain is indeed a cognitive processor. One, therefore, might suppose that coupling and integration can indeed lead to the extension of cognition. One gets the distinct impression that the whole brain is cognitive in virtue of the coupling of the extra-hippocampal regions to the hippocampal regions. The misdirection, however, becomes apparent when we note that, it is perfectly legitimate to suppose that the whole of the brain is indeed a cognitive processor, but not in virtue of the fact that it is coupled or integrated with the hippocampus. What makes the whole of the brain a cognitive processor is the fact that the whole bears the mark of the cognitive? As cognitivists would point out, the whole of the brain realizes processes that transform or manipulate non-derived representations. This has nothing to do with the coupling considerations brought forth by many advocates of the hypothesis of extended cognition.
But, there is also a second way in which one might interpret Hippo-Adams and Hippo-Aizawa more sympathetically. Although it is Clark’s thought experiment and he is free to develop it as he wishes, let us suppose that the Hippo-world brain, just like the real world brain, is a cognitive processor. If so, then by our lights, there will be non-derived representations in the hippocampus and in the extra-hippocampal regions of the brain. Further, in both worlds the brain will carry out transformations or manipulations of these non-derived representations. So, there would be this level of similarity. Nevertheless, there would still be some point to Hippo-Adams and Hippo-Aizawa drawing a theoretical difference between intra-hippocampal processes and extra-hippocampal brain processes. What Hippo-Adams and Hippo-Aizawa might be trying to bring to the attention of the scientific and philosophical community are the ways in which, as a matter of contingent empirical fact, hippocampal processes differs from extra-hippocampal brain processes, not to mention environmental processes. The hippocampus carries out, let us say, spatial mapping of the environment, but not visual or auditory or linguistic processing. Part of what this means is that there are different kinds of information processing going on in the hippocampal and the extra-hippocampal brain regions, not to mention in the external environment. Neither Hippo-Adams and Hippo-Aizawa nor Adams and Aizawa are satisfied to use “cognition” as a label for just any old information processing on non-derived representations. Hippo-Adams and Hippo-Aizawa share with Adams and Aizawa a concern over the indiscriminate lumping together of distinguishable types of processes. Hippo-Adams and Hippo-Aizawa wish to distinguish hippocampus processes from more general “cognitive processes,” where Adams and Aizawa wish to distinguish cognitive processes from more general causal processes. There is sense to what the Hippo-A-Team is saying, just as there is sense to what the Earthly-A-Team is saying. So, it seems that the discussion of Hippo-world does not avoid the tendency to fall prey to the Coupling-Constitution Fallacy.