An externalist rejoinder

There is an important line of response according to which the externalist can concede the point that sameness of behaviour implies sameness of visual content whilst developing the circle- square case in such a way as to generate a genuine counterexample to individualism. The argument in question is due to Davies (1992) and runs thus. It is a mistake to think that twins that inhabit different environments must make just the same bodily movements. If twins live in environments that differ in terms of gravity, or in terms of the density of the medium through which they move, then identical nervous impulses and muscle contractions will issue in subtly

different bodily m ovem ents. Suppose that the respective

environments of Edgar and his twin differ in this kind of way. The very internal phenomena that cause Edgar to trace the shape of a square in the air cause Twin-Edgar to trace the shape of a circle and the very internal phenomena that cause Edgar to walk in a square- wise fashion cause Twin-Edgar to walk in a circle. Hence it is true of both twins that their behaviour constitutes a well adapted response to its distal cause. And thus the behavioural facts do not tell against

there being any breakdown in the relationship between visual state and behaviour. After all, there is no reason why a community couldn't adopt the convention of representing circular-shaped objects by means of squares. Whether or not Twin- Edgar's behaviour could plausibly be interpreted in this light, the response breaks down when it comes to circle-caused behaviour, the primary purpose of which is not to communicate the subject's conception of the shape of whatever object is impinging upon him. The way in which Twin-Edgar handles and circumnavigates circular­ shaped objects is so inappropriate that there is no way of avoiding concluding that he sees them as squares, save accepting that there is a breakdown in the relationship between his visual states and his behaviour.

the attribution of the content square to SI in Edgar and circle to the same state in his twin.

Ingenious though this argument is, I think it fails, as it overlooks an important fact about the way our bodies work. When I make a movement I am usually aware of the nature of the movement that I have made. For example, if I trace a square in the air with my hand I will be aware that I have so behaved. This awareness is a form of conscious experience (I have a sensation of tracing a square with my hand), but does not rely on vision; even with my eyes closed I am sensitive to the way in which I move my limbs. Having this capacity to monitor my movements plays an important role in enabling me to interact successfully with the world. Underlying this capacity are m echanism s w ithin my body that provide my brain w ith information that enables it to determine the extent, direction and velocity of the m ovem ent of my limbs as I behave. These mechanisms will be sensitive not to (or not just to) the nature of the muscular contractions and nervous impulses that cause behaviour, but to such factors as the degree and direction of bone movement w ithin sockets at the joints, and phenomena issuing from these movements such as the tension of ligaments and tendons. When I trace a square with my hand, the activity at my joints is subtly different from that that takes place when I trace a circle. This difference manifests itself in the feedback that my brain receives, which in turn results in my having quite different sensations as to the way in which I have moved. All this is true not just of me but of all humans and, of course, of Twin-Edgar and his fellows.

I concede that identical internal events (muscle contractions, nervous impulses and the like) could cause different bodily movements in twins that inhabit divergent environments. But surely the feedback that these movements generate will differ from one twin to the next. Edgar traces a square with his hand, whereas Twin-Edgar traces a circle. This difference in their respective bodily movements will be reflected in the activity that takes place at their joints; for example, there will be subtle differences in the direction and extent of the motion of bones within the sockets that link them to adjoining bones. If there were no such differences, the twin’s, being twins, would surely make identical bodily movements. Given that the feedback mechanisms are sensitive precisely to such

phenomena, the response of Edgar's mechanism will be intrinsically different from that of his twins corresponding mechanism. Consequently, their subsequent experiences of how they moved will diverge; Edgar will have the experience of tracing a square, whereas Twin-Edgar will have the sort of experience (qualitatively and physically) that Edgar normally has when he traces a circle. The important point is that whatever contents we attribute to the internal feedback states of the twins, the fact is that they will differ at the physical level; that is, they will not be twins. Thus Davies has sketched a highly implausible scenario; twins with bodies that work anything like the way in which our bodies work cannot make different bodily movements. If two individuals move in different ways then they cannot be twins.

Another point worth making is that all this implies that Twin- Edgar will be woefully ill-adapted to his home environment. Suppose that I find myself in an environment like Twin-Edgar's. I see a circular-shaped object which causes a tokening of state 81 (a

state which, according to the externalist, has the content square) and a

visual experience as of a square. I attempt to behave towards this

object in a square-wise fashion, but end up behaving as if it were a circle. With my eyes I will see myself engaging in "square" behaviour but from the inside it will feel like I am behaving in a "circular" fashion. In other words, the information that my brain receives from the visual module will clash with that that it receives from the internal feedback mechanism, and this clash will manifest itself in my being befuddled, experiencing a sense of disquiet, and coming to believe that something has drastically gone wrong. Clearly I would have problems leading a life in this environment if I had much contact with circular and square-shaped objects. To avoid grinding to a halt in a state of utter confusion, I would have to learn to ignore an im portant source of information as to the nature of my bodily movements. And it is difficult to see how a creature like me could have evolved in such an environment.

Twin-Edgar is going to face the same problems in his home environment that I do when I visit. When he is confronted with a circular-shaped object and acts "naturally", he is going to receive mixed messages concerning how he has behaved, mixed messages that will drive him into a state of confusion and a general feeling

that something is going wrong. This will be the case however we describe the contents of his internal states. The only way that Twin- Edgar will be able to overcome this problem will be by learning to ignore either what his eyes tell him in such situations, or what his internal feedback mechanism tells him. But if he has to undergo such a learning procedure he can hardly be well adapted to his environment; it is difficult to see how evolutionary processes could have cooked up a creature like him. And if Twin-Edgar isn't well adapted to his home environment, then he is of not much use to the externalist cause, for what the externalist ideally wants is a case of twins who inhabit radically different environments to which they are equally well adapted. The less well adapted a creature is, the less compelling are the grounds for regarding it as correctly representing its distal stimuli, and thus the less compelling are the grounds for thinking that the nature of its environment is reflected in the contents of its visual states.

I therefore conclude that Davies' attempt to modify the square-circle case fails. In this case, just as in the shadow-crack case, Marr would attribute just the same contents to the corresponding visual states of the twins in question. I think that this result is grounds for scepticism that there are any plausible counterexam ples to individualism; it is difficult to see how there could be a plausible case of well adapted twins who inhabit environments that diverge to such an extent as to tell against the attribution of identical contents. 4.6 Behaviour versus environment

My argument in the preceeeding section relies on the idea that Marr places a great reliance on the behaviour of the subjects whose visual modules he studies. Such a portrayal of Marr's approach might appear to be in tension with the way in which I described his theory at the beginning of this section (and, indeed, with my general account of scientific psychological explanation); for I stressed both that Marr proceeded by reflecting on the nature of the extra-cranial world, and that appeals to facts about that world play a significant role in his theory. Fortunately, this apparent tension can be resolved, and can be resolved in such a way as to undermine Burge's initial externalist argument.

As we have seen, scientific psychologists regard our perceptual and cognitive modules as information-processing systems, systems that generate information from information. To describe a system as generating information from information is to say more than that it generates m eaningful symbols from m eaningful symbols. In addition, it is to imply that the system generates symbols that correctly represent facts about a certain subject matter from symbols that correctly represent facts about some other subject matter. In other words, it is to imply a good deal of success. Thus scientific psychology operates with the idea that our perceptual and cognitive modules are largely successful. In saying this, I do not contradict any of my earlier assertions, as this assumption of success is based upon behavioural evidence and in no way commits the psychologist to the view that cognitive and perceptual modules must by definition be successful; it's just that, in point of empirical fact, our modules are largely reliable.

When a system generates information from information, that it does so, or that it is able to do so, by the means that it employs, has a lot to do with the nature of the world. In general, what information can be generated from what information (and how) is determined by the way the world is. For example, had the world been suitably different I would not be able to extract information about my current bank balance from information about its level at a previous date and all my intervening banking transactions. Thus it is important to highlight the relevant facts about the world in explaining my success; in explaining how I manage to reach true conclusions about how much money I have in my bank account. The same applies to perceptual and cognitive modules; if they are successful, if they do generate information from information, then an explanation of that success must appeal to the relevant (contingent) facts about the world. But none of this implies that the nature of the world external to an information-processing system determines the content of the representations that it manipulates. Suppose that the content of our visual states was individualistic, or was assumed to be so by scientific psychology. It would still be necessary to appeal to relevant facts about the world in order to explain the success of the visual module in generating information or veridical representations, as that success would partly be the product of such external facts. Hence the

fact that scientific psychology (and Marr) appeals to facts about the extra cranial-world does not imply that it (or he) individuates content non-individualistically.

It is true that Marr reflects on features of the world in order to determine how the visual module works, and that there is an important respect in which the contents that he attributes to our visual states is environment driven. But once again this does not tell against his being an individualist. Suppose that you were confronted by a system whose observable behaviour indicated that it solved a certain information-processing problem. What would be the most effective way of determining how the system solved that problem, of explaining its success? A very sensible strategy would be to reflect on the system's environment in order to work out what potential solutions that environment permits, and which it rules out. If a certain solution is discovered to be theoretically possible in that environment, then a hypothesis worthy of consideration is that the system solves the problem in that way.(After all, in any environment there will be only a small number of ways to solve any complex information-processing problem). This hypothesis can then be checked against behavioural evidence. If the behavioural evidence supports the hypothesis then it can be tentatively endorsed, an endorsement which involves attributing certain contents to the system 's internal states. If this strategy is pursued, then an explanation will be constructed by means of a consideration of the world external to the system. And the contents attributed to the system's internal states will be environment driven in the sense that had the environment been significantly different, then a different explanation would have been generated, and thus different contents attributed.

To adopt this strategy is not thereby to individuate the contents one attributes to the system in question non-individualistically. Someone who adopted the strategy and endorsed the resultant explanation would be free to regard the internal states of all the system's twins as having just the same content no m atter w hat their home environment was like. It's just that she would be forced to concede that some of those twins would systematically generate false answers to the information-processing problem that they attempted to solve.

The strategy that I have described is a simplified version of that employed by Marr. It involves considering both behaviour and the extra-cranial environment. Consideration of behaviour helps to determine the extent of the visual module's success, and to choose between alternative candidate explanations of that success. And consideration of the environment helps to generate such candidate explanations, and reveal why the visual module's operations work to the extent that they do.^^ Thus, by parity of reasoning, Marr's approach is consistent w ith his individuating visual content individualistically; that he examines the extra-cranial world, and that his content attributions are environment driven, merely reflects the fact that he (on the basis of an observation of our behaviour) is of the opinion that the hum an visual module is largely successful in generating veridical representations of the external world from retinal images.

This, I take it, resolves the tension between, on the one hand, the claim that Marr is sensitive to behaviour in the way that I have described and, on the other hand, the claim that a consideration of the environment and an appeal to environmental factors plays a fundamental role in Marr's approach, and theory. It also serves to underm ine Burge's argum ent by indicating how the success- orientation of M arr's approach and the fact that his content attributions are environm ent driven, is consistent w ith his individuating visual content individualistically.

In a little more detail: Human behaviour suggests to Marr that we generally correctly represent such properties of objects as their shape, size, colour, surface markings, motion, and the like: hence that behaviour indicates that the visual module succeeds in working out the shape, size, colour, surface markings, motion, and the like, of distal stimuli from the retinal images that it takes as input. Given that the visual module's ability to do this partly depends on the nature of the extra- cranial world, Marr reflects on the nature of that world for cues as to just how it does it. Candidate explanations generated in this way can then be checked off against behavioural evidence. For example, our performance in the task of categorising objects on the basis of stick figure representations of them supports the idea that the visual module represents the shape of objects as, or by means of, generalised cones or collections of generalised cones.

4.7 Conclusion

I therefore conclude that the case against M arr’s being an

individualist is unconvincing. Neither the crack-shadow nor the circle-square case can be developed in such a way as to tell against indivdualism. Moreover, it is consistent with the success-orientation of Marr's theory, and the fact that he appeals to contingent facts about our environment, that Marrian contents are locally supervenient. However, that is not to say that Marr employs a notion of narrow content in the sense of a type of content divergent from that employed by ordinary folk (or one that is unfamiliar from the folk perspective). Of course some of the representations that figure in Marr's theory (the primal sketch and the 2i/2-D sketch, for example) are unfamiliar. But many of the properties that these representations express, and thus the contents that they have, are familiar enough. After all, what is so strange about a representation representing an object as being square-shaped or as having a small dark mark on its surface? This point hints at a way of reconciling the conclusion of this chapter with the line I developed in Chapter 3.

In Chapter 3 I argued that due to the practical problems of "going narrow" scientific psychology should not employ a notion of narrow content if at all possible, and suggested that it is indeed possible to avoid narrow content. I also attempted to undermine various pro­