Clark Dynamical Challange 1997

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    COGNITIVE SC IENCE Vol21 4) 1997, pp. 461-481 ISSN 0364-02 13Copyright 0 1997 Cognitive Science Society, Inc. All rights of reproduction in any form reserved.

    The Dynam ical ChallengeANDY CLARK

    Washington niversity

    Rec ent studies such as Thelen and Smith 1994), Kelso, 1995), Van Gelder,199~3, Beer, 1995), and others have presented a forceful case for a dynam-

    ica l systems approach to understanding cognition and adaptive behavior.These studies call into question some foundational assumptions conc erningthe nature of cognitive scientific explanation and in particular) the role ofnotions such as internal representation and computation. These are exc itingand important challenges. But they must be handled with c are. It is all tooeasy, in this debate, to lose sight of the explanatorily important issues and totalk at cross-purposes, courtesy of the surprisingly) various ways in which dif-ferent theorists often conceive the key terms. The primary goal of the presentpaper is thus a modest one: to begin to c larify just what is at issue and to high-light some of the most central and pressing conc erns. In so doing, we mayhope to develop a constructive framework for future debate. In addition, I tryto open up a space of intermediate options-ways in which dynamica l andrepresentational/computational understandings may sometimes afford com-plementary rather than competing) perspec tives on adaptive success.

    1. A NASCENT SCEPTICISMThese are exciting times for Cognitive Science. Once-unchallenged ideas concerning thenature of internal representational systems have been upset by the explosion of interest inconnectionist and neural network mod els. Mo re recently still, even the bedrock notions ofinternal representation and computational explanation themselves have been subject toincreasing critical scrutiny. In particular, several theo rists concern ed to do justice to thespecial nature of embod ied intelligent systems have endorsed versions of a rather radicalclaim which goes something-like this:

    The Radical Em bodied Cog nition Thesis: Structured, Symbolic, Representational andCom putational views of cognition are mistaken. E mbo died cognition is best studiedusing non-computational and non-representational ideas and explanatory schem esinvolving e.g. the tools of Dynamical Systems Th eory.

    Direct all correspondence to: Andy Clark, Philosophy/Neuroscience/Psychology Program, Department of Philos-ophy, Washington University, St. Louis, MO 63 130; E-Mail: andy@twinearth.wustl.edu.-

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    462 CLARK

    Versions of this thesis can be found, for examp le, in recent w ork in developmental psy-chology (Thelen & Smith, 199 4, Thelen, 199 5), work on real-world robotics and autono-mous agent theory (Smithers, 1994 , Broo ks, 199 1), in philosophical treatments such asWh eeler (1994 ), and in some neuroscientific and neurobiological appro aches such as Mat-urana & Varela (198 0), Skarda and Freeman (1987 ). Mo re circumspect treatments whichnonetheless tend towa rds scepticism about compu tation and internal representation includeBeer and Gallagher (1992 ), Beer (1995 ), Kelso (1995), Van Gelder (1 995), V arela,Thom pson and Ro sch (19 91), and essays in Port and Van Gelder (1995 ). Historical prece-dents for such scepticism are also in vogue and include especially Heideg ger (1927: 1965 ),Merleau-Ponty (1945: 196 2), and the wo rk of J.J. Gibson and the ecological psycholog ists(e.g. Gibson, 197 9).

    The Radical Emb odied Cognition Thesis constitutes, I believe, one of the most impor-tant and challenging developments in contempo rary cognitive science. But it is a develop-ment wh ose genuine value is easily obscured by terminological misunderstandings (thewo rd representation being an especially slippery case ) and knee-jerk reactions (its justbehaviorism, or, on the other side, cartesianism). The goal of the present paper is to clarifythe nature of the genuine, open, em pirical questions that are at issue and to develop aframew ork for constructive future debate. In addition, I shall try to open up a space of inter-mediate options-ways in which dynamical and representational tools may afford comple-mentary (not competing) perspectives on adaptive success.

    The strategy is as follows. I next (section 2) outline four ways in which the slippery termrepresentation may be used. Of these four, only the last two constitute substantive, empir-ically significant options. Section 3 pursues some case studies of dynamical explanationand tries to identify a few guiding ideas. In section 4 I identify some assumptions that mayseem to bridge the large prima facie gap between these ideas and the thesis o f radicalembod ied cognition. I question these assumptions and, as a result, the relevance of theguiding ideas to the radical conclusions. Wh at emerg es, I hop e, is a clearer sense of wha treally distinguishes the dynamical approach-namely a deep difference in explanatoryemph asis (roughly, it is the difference between aiming to explain patterns and aiming tounderstand architectures). Section 5 pursues this difference, asks how the two projectsinterrelate, and suggests some ways in which they may ultimately prove complementary toone another. The concluding section draws the se threads together to paint a picture of themain issues, and to (hopefully) clarify the space for future d ebate.

    2. UNPACKING REPRESENTATIONThe term internal representation has long stood firm as part of the basic infrastructure ofcognitive scientific research and experimentation. Connectionists, it is true, diverged fromtradition by putting their faith (for the most part) in a more implicit style of representing:they replac ed the stable, simple, highly-manipu lable symb ols of classical Artificial Intelli-gence with numerical vectors and operations of vector completion and transformation. Butthough the computational profile differed, the basic commitment to a vision of intelligentbehav ior as involving the creation and use of internal represe ntations remained inviolate.2

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    DYNAMICALCHALLENGE 46

    Contem porary critics of representational approa ches tend, as we shall see, to distrustboth classical and connection&t species of representationalism, though they typicallybelieve the connectionists to be on the right track-see e.g., (Wheeler, 1994 ), (VanGelder, 1993 , (Thelen & Smith, 199 5) and others. O ur immediate task, then, is to begin toclarify the (clearly quite general) sense of internal represen tation that look s to be at issue.

    Let us begin with the weak est possible sense-one with which no one takes issue,except to note th at it is so weak as to be totally uninformative. This is just the bare idea o finternal state. It is agre ed on all sides that flexible, adap tive, intelligent behav ior oftenrequires a creature to respond to current situations in ways informed by past experience,on-going goals and the like. Systems that merely react, in a pre-determined way, to imme-diate stimuli (that will always react the same way to the same stimulus) are unable toachieve this flexibility. Wh at is needed is, at a minimum, the use of inner state to allow theagent to initiate and organ ize behav ior witho ut immediate environmen tal input, to antici-pate future environmental inputs, and so on. In short, merely reactive agents are clearlyinadequate to the full range of intelligent adaptive behaviors exhibited by biological organ-isms. Com plex persisting and updatable inner state is thus at the heart of many (probablyall) genuinely cognitive phenom ena. This much must be comm on ground to both fans andsceptics about internal representation. The existence and importance of comp lex inner stateis thus not at issue.3

    Moving up a notch from the bare notion of inner state, we encounter the only slightlyless vacuous notion o f environmentally-correlated inner state. On its own, how ever, thisrequirement of correlation adds little to the bare idea of inner state. It would, after all, bealmost m iraculous if some kind of correlations between adaptively useful inner states andadaptively relevant environmental param eters did not exist. Mo reover, correlation comesche ap (mappings can alway s be artificially defined ) and is not necessarily even function-ally illuminating. Thus Churchland & Sejnowski, (1992 , pp. 185-1 86) describe a neuralnetwork in which certain hidden unit activities correlate rather nicely with the presence ofedges-but the systemic role of these units is, in fact, not to do edge d etection at all but tohelp extract curvature from shade d im ages. In sum, the bare idea of correlations betweeninner states and worldly features does not provide a substantial and illuminating sense forthe term internal representation.The crucial m oment in the transition to a genuinely substantive reading com es, instead,when we abandon the focus on mere inner state and/or correlation and replace it with afocus on the relation mo st usually gloss ed a s standing-in. All substantive notions of inter-nal representation, I am willing to assert, have at their heart some idea of inner states (orprocesses) wh ose real functional role is to stand-in for other (usually extra-neural) objects,events, actions o r states of affairs. Thus the philosoph er John Haugeland insists (rightly)that representation-using systems are ones that achieve some kind of coordination withenvironmental features by the special m ethod of having something else (in place of a signaldirectly received from the environment) stand-in and guide behavior in its stead (Haug e-land, 199 1, p. 144).

    It is immediately apparent, how ever, that this notion of standing-in must now be treatedwith caution. For it