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Philosophical Foundations of Neuroscience was written at the beginning of the century. It has been widely read and often cited, and has provoked extensive debate that, we hope, has been fruitful. Our publishers, Wiley Blackwell, suggested that we write a second edition to bring the book up to date in the light of the discoveries, new theories and novel conjectures that have emerged in the field of cognitive neuroscience over the last two decades. They offered us the possibility of extending the book by an extra hundred pages in order to do so.

After careful deliberation we decided to accede to the request. This introduction to the new edition is directed primarily at readers of the first edition who wish to know why we thought fit to write a second edition, and would like to attain an overview of what we have added or modified.

Four reasons moved us:

First, new technical developments in neuroscience, such as fMRI, were often highly problematic and new discoveries concerning blindsight and commisurotomy challenged previously received understanding. This called out for systematic clarification. Moreover, new cognitive neuroscientific doctrines were developed by Tononi and Dehaene and their research groups and demanded conceptual elucidation and evaluation.

In the twenty years since the first edition of this work there have been very substantial increases in the literature of cognitive neuroscience devoted to subjects of interest in the present work. This has required an updating of our discussions of the neuroscientific literature. For example, the over 500,000 papers using functional magnetic resonance imaging ( f MRI ), many of which are concerned with localization of brain function in relation to the exercise of psychological powers, have necessitated a brief description of this technique, introduced by Ogawa following Sherrington. This is given in §1.7 [§§1.7.1–1.7.2]. Recent observations that have been made on the origins of the Readiness Potential, used by Libet to support the claim that willed volitional movements are preceded by the early components of this potential, are sketched in §9.2. ‘Blindsight’ is a phenomenon, first researched in the twentieth century by Weiskrantz, which, in the first edition of Philosophical Foundations of Neuroscience, we showed to have been misinterpreted as a disconnect of a monitoring function in the brain that mediates sensation and perception. It is now thought to have a quite different explanation by reference to an alternative pathway that bypasses the visual striate cortex altogether. Commissurotomy was argued many decades ago by Sperry and Gazzaniga to give rise to ‘two minds’ in the same brain, a claim which again required conceptual clarification and criticism. Like ‘blindsight’, this too has now been challenged on neurophysiological grounds. We comment on the new observations concerning both these phenomena in chapter 17. Finally, there are theories on how the brain supports consciousness based on recent neuroscientific observations that require extensive connective conceptual analysis, such as the Integrated Information Theory of Tononi and the Global Workspace Theory of Dehaene. This analysis is provided in chapter 12.

This is a work of philosophical or conceptual clarification, so we have attempted to keep the technical aspects of neuroscience to a minimum. ( Extensive technical discussions are to be found in our 2008 book History of Cognitive Neuroscience.) But what we have introduced should help sketch the contemporary landscape of that subject, whose actual achievements need clarification.

Second, there was a misunderstanding concerning the subject of the book. Many reviewers and critics thought that the central subject of Philosophical Foundations of Neuroscience was the mereological fallacy in neuroscience, that is: the mistake of ascribing to the brain – a mere part of the human being, and to parts of the brain – such as the visual striate cortex, the frontal cortices, the amygdala and so forth, psychological, intellectual and volitional attributes which can logically be attributed only to the human being as a whole. This categorial mistake leads to flaws in reasoning, that is: to fallacies. We gave the impression to some reviewers that all 452 pages of the first edition were dedicated to displaying this mistake and refuting this fallacy. But this is to mistake a leitmotif for the opera itself. In the first edition, we dedicated a part of chapter 3 to the matter of ascribing to parts of the brain properties of the organism as a whole. In the new edition we have segregated this into an independent (chapter 3), separating it from a range of further fundamental conceptual entanglements (chapter 4). These include the subjects of self-ascription of experience, of introspection as a form of inner sense, of knowledge of the mental states, events and processes of other people, of privacy and subjectivity, of identity of experiences, of naming and describing experiences and of constitutive evidential grounds. These misunderstandings are not aspects of the mereological fallacy in neuroscience. They are severally and collectively no less important.

It is perfectly true that the mereological principle and the mereological fallacy run like a leitmotif through the book. But that is because this pervasive mistake causes misunderstandings, misinterpretations of the results of experiments and faulty design of experiments. So we could not avoid mentioning it in our conceptual investigations into the forms and structures of human faculties and their exercise. However, our general explanation is to be found in chapter 3 and is now clearly separated from other important conceptual flaws.

Third, Philosophical Foundations of Neuroscience was and is designed as a handbook for cognitive neuroscientists, a handbook to be consulted before commencing conceptualization and design of experiments on specific human faculties and their exercise. Reviewers and philosophers apart, we do not expect many of our cognitive neuroscientist readers to read through the whole book at successive sittings. For most such readers, this is a reference work, Parts II and III of which are to be consulted chapter by chapter as necessary. ( That is why we have allowed a fair amount of overlap and some repetition, so that each chapter should be reasonably self-contained.) The chapters in Part II cover the themes of sensation; perception; knowledge; memory; belief; thinking; mental imagery; perturbations, agitations and emotions; voluntary movement, voluntary, purposive and intentional action; executive control; automatic and mechanical behaviour. Part III is concerned with a battery of topics linked with consciousness, and has little to add on mereological errors. Its purpose is to shed light on a wide range of themes that preoccupy contemporary neuroscientists: on intransitive and transitive consciousness, on perceptual consciousness and consciousness of facts, on self-consciousness in its manifold forms and on qualia or the so-called qualitative character of experience.

Fourth, many neuroscientists and cognitive psychologists may be puzzled why philosophical analysis of salient concepts should have any relevance to the experimental neuroscientist. Some think that philosophy is now obsolete, that the great problems of philosophy over the last two and a half thousand years are destined to be resolved by study of the brain. Neuroscience, many believe, is solving the venerable problem of free will – showing experimentally that freedom of action is a delusion produced by the brain. Similarly, it is widely believed that the cognitive neuroscience of perception proves that perceptual qualities, such as sound and colour, do not exist in the ‘external world’, but are fictions produced by the brain, in the brain. Others demonstrate to their satisfaction that memories are stored in the brain at synaptic connections or cells – a modern variant of engrams. American neuroscientists commonly appeal to the 1890s work of William James as the still unsurpassed work of psychology and cognitive science. As we show, James’ s book The Principles of Psychology is a goldmine of conceptual confusions, from which much can be learned.

One reason for the widespread belief that philosophy is obsolete is that, with a history of more than two thousand years, philosophers are still alleged to be arguing over the same old problems that preoccupied Plato and Aristotle. But this is both an exaggeration and a misunderstanding. It is an exaggeration in as much as there are numerous philosophical questions that do not and could not appear in the works of Plato and Aristotle, such as the nature of alternative geometries, the post-Einsteinian puzzles about space-time, the differences between the voluntary and the intentional. It is a misunderstanding in as much as neuroscientists do not realise why so many of the deepest problems of philosophy have to crop up, in slightly different forms, every generation and have to be tackled de novo by each generation. This we try to explain by reference to the fact that the potentiality for conceptual confusion is buried deep in our language. Such confusions can be eliminated for a few decades by painstaking conceptual analysis. But they will rise again, as younger generations fall into the same traps. Sense data died under critical onslaught in the 1950s and 1960s, but by the end of the century internal representations arose phoenixlike from their ashes.

Numerous scientists find puzzling the thought that a priori reflection can have any bearing on experimental science, and that experimental science, while it can present new conceptual problems for connective analysis, cannot show logico-grammatical analyses to be mistaken. It is surely impossible that a few minutes’ armchair reflection on the use of a couple of words in English should be able to trump painstaking experiments of the greatest sophistication, using instruments that probe the functioning of the brain, that are successfully repeated all over the world. It seems equally baffling to suggest that a well-constructed neuroscientific experiment should not be able to prove false the grammatical conventions of a prescientific language concerned with perception, thought, affection and will in all their forms. Logico-grammatical analysis investigates mere words, but neuroscientists are concerned with reality. Cartesian dualism, it is argued, was shown to be false by the discovery of the law of conservation of momentum. That an immaterial substance might affect the total quantity of momentum would violate the laws of physics.

This is mistaken. Cartesian dualism is not shown to be false by the advance of science, for science can show something to be false only if it makes sense. If it makes sense then it is intelligible that it be true even though it happens not to be. If the Cartesian mind were able to change the direction of motion of the body by acting on the pineal gland, then the so called system of the physical universe would not be closed, as philosophers of science commonly suppose it to be, and the Law of Conservation of Momentum would be false. But the flaw in Cartesian dualism (or, more generally, substance-dualism) is not that it is false but that it is not coherent. It makes no sense, because the idea of an immaterial, spiritual substance is incoherent. It lacks both synchronic and diachronic criteria of identity. The idea that an immaterial substance might be an active agent in the material world, with the powers to causally affect the pineal gland by acting on it thereby releasing animal spirits into the nerves, makes no sense. It is not a false theory but an incoherent conjecture.

Conceptual analysis is to neuroscience what the differential calculus is to physics: a neuroscientist cannot do without it, whether he likes it or not. He can take for granted a received conception, often rooted in past defective analyses (e.g. by William James or by von Helmholtz ), or he can confront the received assumptions and reflect on them. It is for those striving to think for themselves that we offer our work as a set of guidelines. For on most of the major themes of cognitive neuroscientific research we try to provide the major conceptual characterizations, depicting the logical geography of the domain.

Conceptual mistakes have real consequences, for our concepts unavoidably guide both practice and interpretation. These consequences in neuroscience are of at least three kinds. First, if a neuroscientific experiment misconstrues its actual subject matter, then no matter how internally consistent it is, its results will have no practical, real-world implications, since its results are hermetic to the misguided framework within which the experiment is constructed. An example here is Libet’ s conception of voluntary action, which has not in practice stopped anyone from changing their behaviour in the several hundred millisecond interval preceding the movement with regard to which we are allegedly mere automata. Second, an incoherent scientific theory built on perfectly valid data will fail in inductive, predictive reasoning, just as an equation in physics that contains a covert division by zero will fail in its predictive use. Once the incoherence has been realized, one need not wait for the zero values to be entered into the equation to know that a theory based on such an equation is going to be worthless. Hence investigations of the neuroscience of memory that rest on the assumption that memory is of or about the past, or that memory is exhibited by any change of behaviour consequent upon prior experience, can be rejected in advance of any experiment. For memory is acquired in the past, but it need not be of the past – it may be of or about the present, the future, omnitemporal or atemporal; and wricking one’ s ankle and thereafter limping is not remembering anything. Third, whether predictive or not, a scientific theory that is conceptually flawed cannot be explanatory. For explanation, even more than prediction, depends on the coherence and integrity of the conceptual framework within which it is constructed, no less than upon the empirical data it brings to bear on the explanandum. Of course, the empirical consequences of conceptual errors in neuroscience are not typically immediately obvious, especially when widely accepted by groups of working neuroscientists. However, such errors are not stochastic: if something makes no sense, there is no chance that it will later spontaneously acquire sense as the experiments unfold. It is true that in the past important discoveries have been made despite incoherent theories. But that is not a recommendation for incoherence. Incoherence is not an infantile disease that neuroscientific theories catch before they mature into received neuroscientific wisdom.

Does all this mean that neuroscientists have to study philosophy or to become philosophers? No – there are great swathes of philosophy, such as metaphysics, logic, philosophy of mathematics, or moral and political philosophy that are of no concern to the neuroscientist. Nevertheless, many of the conceptual structures presupposed in neuroscientific research and the specific conceptual forms invoked are, by their nature, highly problematic. For they unavoidably link the conceptually heterogeneous domains of the behavioural, the psychological and the neural. Furthermore, neuroscientists are sometimes required to extend existing concepts or to introduce new concepts for specialized purposes. It is all too easy to do so in inconsistent and incoherent ways. It is desirable that neuroscientists be familiar with connective analytic methods in order to sharpen their sensitivity to conceptual unclarities, errors and confusions. They must be able to realize that, for example, memory need not be of the past, that one cannot order someone to be conscious of something, that if one is conscious of something’ s being so, then it follows that it is so, that something may be voluntary without being intentional or intentional without being voluntary, and so on. They cannot stand aloof from conceptual questions or refrain from committing themselves to conceptual forms.

It will come as no surprise to those who have read the first edition of this book that a spirit hovers over its arguments: the spirit of Ludwig Wittgenstein. Why Wittgenstein rather than Popper (who inspired Eccles ) or even Locke (who inspired von Helmholtz )? Because Wittgenstein’ s reflections on the philosophy of psychology surpass anything previously achieved in this domain of philosophical thought. Our conceptual analyses in this book echo and elaborate Wittgenstein’ s not because we are fond of Wittgenstein but because his intellectual approach in this domain is precisely what is needed by cognitive neuroscience. Philosophy of psychology has to elucidate the conceptual relations between the behavioural and the ‘inner’, ‘mental’ or ‘psychological’. It has to account for the conceptual structures that inform the asymmetries between the first-person utterance and the third-person description of ‘experience’ or ‘states of consciousness’. Wittgenstein broke with a long tradition of conceptual confusion characteristic of both rationalist and empiricist thought, indeed a tradition dating back to antiquity. He ploughed up the field of philosophical thought afresh. Cognitive neuroscience was firmly planted in that field, with roots reaching down to the late fifteenth and sixteenth centuries, as we describe in chapter 1. It has to cope with a subject matter that straddles the behavioural and the ‘inner’, although here the ‘inner’ is neural and cortical. The basic observation statements of the science are what people do and say, and it is these that need to be related to an ‘inner’. Here too there is an illusion that just as introspection seems to bypass behaviour and give one direct access to an ‘inner’, so too positron emission tomography ( PET ) and functional magnetic resonance imaging (f MRI ) give neuroscientists the illusion that they can bypass behaviour and study the ‘real thing’ directly. At last, as one well-known neuroscientist exclaimed, we can ‘actually see thought’. But that too is an illusion. For neuroscientists, the ‘hard facts’ are recurrent and reproducible human behaviour. We can see thought when we watch Le Penseur and hear thought when we listen to a great thinker lecturing, but not when we watch the computer-generated image of an fMRI scan.

Finally, to mention a theme that will recurrently preoccupy us throughout the methodological sections of this book, critics seem puzzled at the idea that examination of language can have anything to tell empirical scientists other than linguists. The puzzlement seems to have two sources: first, the thought that language is trivial, whereas neuroscience is deep; second, that an interest in current psychological or mental vocabulary precludes conceptual and linguistic change. Both are mistaken. Since it is the capacity to speak and the mastery of a language that is a condition of all that is distinctively human, and hence too a condition for the sciences and the arts of humanity, it is hardly appropriate to trivialize what differentiates us from monkeys and rats. Without a mature language there is no formulation of scientific hypotheses and so too no discovery of general truths of neuroscience or of science in general. The scrutiny of the language of psychology and neuroscience will not discover new neuroscientific truths, but it will guard against the inadvertent adoption of incoherent hypotheses and the illusory confirmation of unintelligible neuroscientific conjectures. Language, and the concepts expressed in our languages, are the medium of scientific thought. If one ties knots in the web of words, one can get nothing right, save per accidens – and even should one be so fortunate, one will not understand what one has discovered. Second, that we need to examine our means of representation carefully in order to avoid the manifold confusions to which we are prone does not imply that we are confined to our existing vocabulary and the concepts it expresses. Nothing prevents linguistic stipulation and conceptual innovation. But we must be forewarned to ensure coherence, and to assure that the innovation dovetails smoothly into antecedent usage. Analogical extension needs meticulous monitoring, lest it be stretched beyond the bounds of intelligibility. The step from ‘as it were’ or ‘it is as if’ to ‘it is so’ is far too easy to take, as is patent in the development of talk of dictionaries and concept-stores in the brain. It is self-defeating to appeal to pragmatism, as if experiments could validate analogies independently of laying down verifiable criteria of identity and difference (the extension of hydrodynamic analogies to electricity theory is not self-validating or self-confirming ).

In this book we sketch an overview of some of the most widespread and damaging conceptual confusions in cognitive neuroscience. Almost all the chapters of the first edition have undergone revision and addition, sometimes minor, sometimes major. Some revisions have involved correction of previous error (e.g. phantom pain location), others involve additional explanation and elucidation. Most new sections involve reference to and critical discussion of papers published on the subjects of concern over the last two decades. We provide a handbook that we hope will be of service for neuroscientific research. Above all, we try to exemplify an array of analytic methods of conceptual clarification. These methods require no laboratory space and need no grants. All they require is an open mind, a willingness to raise a question for every answer, and patient intellectual effort. This can save a young scientist from committing his or her life to an enterprise that was doomed to failure before it even started (e.g. the quest for the neural correlates for qualia – see chapter 11 – or the search for the locus of the self – chapter 14).

We have added to this second edition numerous figures, charts and tree-diagrams, comparative lists and tables. They are meant to facilitate obtaining an overview of a conceptual domain – providing a synoptic presentation that can be taken in at a glance. They are often no more than illustrations to the argument of the text, not substitutes for it. They sometimes oversimplify for purposes of surveyability. So they should be used with care. With this proviso, we believe that they fulfil a useful function in aiding understanding.

M. R. Bennett

P. M. S. Hacker