Abstract Multiple realization was once taken to be a challenge to reductionist visions, especially within cognitive science, and a foundation of the "antireductionist consensus." More recently, multiple realization has come to be challenged on naturalistic grounds, as well as on more "metaphysical" grounds. Within cognitive science, one focal issue concerns the role of neural plasticity for addressing these issues. If reorganization maintains the same cognitive functions, that supports claims for multiple realization. I take up the reorganization involved in language dysfunctions to deal with questions concerned with multiple realization and neural plasticity. Beginning with Broca’s case for localization and the nineteenth century discussion of "reorganization," and returning to more recent evidence for neural plasticity, I argue that, in the end, there is substantial support for multiple realization in cognitive systems; I further argue that this is wholly consistent with a recognition of methodological pluralism in cognitive science. (..) it is plausible to think that there are as many levels of description available as there are levels of organization (cf. Lycan 1986) (..) We may describe humans in terms of their physical make-up, their chemical constitution, their physiological structure, their gross anatomy, their cognitive capacities, their social role, and much more. All these give a distinctive perspective on human psychology. (..) a given functionally defined system can apparently be realized - perhaps only in principle, or perhaps in actuality - in a wide variety of material forms with varying constitutions (..) Any realistic account of identity of psychological type needs to accommodate this natural variation [between individuals of the same species]. (..) even within the same species, there may not be a uniform physical realization for what certainly seems the same function (..) We hardly understand the psychology of human pain, much less the neuroscience that might explain it; and it is not true that the psychology can readily be separated from the physiology. (..) In the end, there is no particularly clear way to distinguish kinds of eyes, and so no principled reason to favor one of these views over the other. "Eye" is evidently not a particularly useful kind. (..) As a result, however tantalizing, eyes are not an especially compelling as a case of multiple realization. (..) Advocates of multiple realization, such as Jerry Fodor and Hilary Putnam, also overstated the implications of multiple realization. (..) I see science as hierarchically organized, with multiple levels of explanation corresponding to multiple levels of organization. Explanations may be geared to various levels, or to one, depending on the questions asked, and the experimental tools that are available. (..) RobertMcCauley and Bechtel have a series of papers pressing for the fruits of interlevel integration - which they call "explanatory pluralism" (Bechtel and Mundale 1999; McCauley and Bechtel 2001; McCauley 1996, 2007). (..) The problem is one of finding, as they say, "units of analysis between levels that are of comparable grain." (..) if what we want to explain is why a stick partially immersed appears bent, we do not need, or want, an explanation in terms of neural structures. Optics suffices. So while convergence may be desirable, sometimes it is sacrificed in favor of greater generality, or scope. There are many explanatory virtues. (..) Wimsatt (2007) has for a number of years pressed for explanatory pluralism, though not under that title. Theoretical conceptions of entities at different levels coevolve and are mutually elaborated (particularly at places where they "touch" - where we come closest to having inter-level translations) under the pressure of one another and "outside" influences. (2007, p. 252) (..) Mendelism certainly captures significant patterns in the world. (..) Acknowledging linkage, and chromosome structure, explains some things that Mendelism does not. Shifting to amolecular level explains yet different things. (..) the several perspectives supplement and enhance one another. Identities play a key role in this co-evolution of theories.Wimsatt says that "Morgan’s gene is themolecular gene, at a different level of description, and conversely" (p. 265). (..) Identifications are the tool for expanding our explanatory resources, and not for reducing them. (..) Wimsatt: The multiple-realizability of higher-level properties or types is a general fact of nature, and applied to any descriptions of entities at two different levels of organization. (2007, p. 217) (..) What I want to do here is illustrate the fact that there is a similar kind of case to be made for multiple realization within cognitive science (..) The root problem is understanding what would count as a plausible criterion of psychological equivalence. This is the problem of the One, as Donald Gustafson aptly described it. There is also a problem of the Many, which requires articulating a principled reason for thinking the ‘many’ realizations are actually many realizations, rather then variations on a single theme. Navigating the problems associated with multiple realization is a matter of negotiating both the problem of the one and the problem of the many at once. (..) It is clear that the crucial regions identified by Broca and Wenicke are involved in language; it is less clear exactly what contributions they make to our abilities. (..) It is also clear from imaging data that there are a great number of other regions involved in one way or another in language processing, including much of the left hemisphere and substantial parts of the right hemisphere (especially the temporal lobes and occipital lobes). (..) Language is clearly not a single faculty, but a complex one which involves much more than the classical language areas (..) This is a crucial recognition for assessing multiple realization. (..) Still, despite the uncertainties, a number of points remain relatively fixed. Broca’s area (or Broadmann areas 44 and 45) is clearly implicated in speech production. Wernicke’s area (or Broadmann area 22) is clearly involved in word comprehension, even though the right hemisphere is also involved. There is, moreover, substantial and clear support for left cerebral dominance. Given these fixed points, there is considerable latitude for reinterpretation. (..) Children suffering from extreme trauma can often relearn language, rather than simply exhibiting recovery. (..) The phenomena involved in "recovery of function" indicate, at most, that there are alternative regions capable of realizing some of the functions that are lost. (..) The thought is that there are alternatives to those which do normally carry out the functions. Reorganization is evidently a pervasive phenomenon in neural organization. This is multiple realization. (..) I do think there is little alternative but to embrace multiple realization in the face of the substantial literature on recovery of function in connection with language use. The combination of the doctrine of cerebral dominance together with reorganization requires that there be alternative realizations of the same psychological capacities. (..) The second moral is a broad support for methodological pluralism, for the thought that scientific disciplines develop best under the influence of collaborators. This is the more important and positive moral. We actually do find significant coevolution among disciplines. From Broca’s faculty psychology to Ferrier’s associationism, the neuroscience did in fact accommodate the psychology; and of course therewas accommodation of psychology to neuroscience. This is mutual adjustment, or coadaptation, and not a simple reductionism. |