Wittgenstein On Psychology

13 August 2002/testwitt/frem3

1

TESTING WITTGENSTEIN’S DISMISSAL OF EXPERIMENTAL PSYCHOLOGY AGAINST EXAMPLES Stewart Candlish 0. Background One of the most notorious — and dismissive — passages in Wittgenstein’s Philosophical Investigations is Part II section xiv, which begins like this: The confusion and barrenness of psychology is not to be explained by calling it a “young science”; its state is not comparable with that of physics, for instance, in its beginnings. (Rather with that of certain branches of mathematics. Set theory.) For in psychology there are experimental methods and conceptual confusion. (As in the other case conceptual confusion and methods of proof.) The existence of the experimental method makes us think we have the means of solving the problems which trouble us; though problem and method pass one another by. Strong words. But we know that at one stage in his life Wittgenstein’s interest in psychology was sufficient for him to have done some experimental research, and that he was well acquainted with the work of at least some of the prominent psychologists active in his own lifetime. That is, his quoted remarks were not made from ignorance; and we should accordingly take them seriously enough to consider why he made them, what he had in mind, and to what extent — if any — they may have been (and, though this was all a long time ago, may still be) justified. I shall suggest that one of the things which may have prompted these accusations is the commitment of at least some experimental psychologists to the investigation of various kinds of private objects. I shall try to show, using a couple of examples of these kinds, why the existence of such objects can seem undeniable, and some ways in which Wittgenstein tried to undermine this impression. And I shall show that this commitment to private objects is not confined to the psychologists of Wittgenstein’s time: if the notion of the private object is confused,then there is still conceptual confusion in psychology.1 What are private objects? They appear in Wittgenstein’s thought as the referents of the names in a so-called ‘private language’. In §243 of Philosophical Investigations he explains the idea of a private language thus: The words of this language are to refer to what can be known only to the speaker; to his immediate, private, sensations. So another cannot understand the language. [My translation.] This is not intended to cover (easily imaginable) cases of recording one’s experiences in a personal code, for such a code, however obscure in fact, could in principle be deciphered. What Wittgenstein had in mind is a language conceived as necessarily comprehensible only to its single originator because the things which define its vocabulary are necessarily inaccessible to others. They are, that is, private objects. 1

I shall not try to show here that the notion is confused. (This large undertaking needs its own occasion; anyone wishing to pursue the matter could start with Candlish 1996/1998.) My concern here is what follows for psychology if it is.

13 August 2002/testwitt/frem3

2

Immediately after introducing the idea, Wittgenstein goes on to argue that there can’t be such a language. The argument is quickly summarized. The conclusion is that a language in principle unintelligible to anyone but its originating user is impossible. The reason for this is that such a so-called language would, necessarily, be unintelligible to its supposed originator too, for he would be unable to establish meanings for its putative signs. The importance of drawing attention to the then largely unheard-of notion of a private language and then arguing that it is unrealizable lies in the fact that an unformulated reliance on the possibility of a such a language is arguably essential to mainstream epistemology, philosophy of mind and metaphysics. Such reliance now extends from Descartes to versions of the representational theory of mind which have been prominent in late twentieth century cognitive science. My focus here, however, will be more restricted than this. 1. Private Objects But what exactly is Wittgenstein’s notion of a private object? One problem with this question is that, because he uses the phrase ‘private object’ to capture a confusion, a fully specified account of the notion is unavailable (in much the same way that one cannot fully specify a method for an impossible mathematical construction). This makes even the suggestion that there are no private objects fraught with difficulty. Still, the phrase captures an inclination, which all of us feel on occasion, to think of oneself as having sole access to inner objects through introspection — the immediate contents of consciousness — with each person’s set of objects hidden from every other person. One of the passages which best displays Wittgenstein’s reaction to this inclination is in Part Two of the Investigations (p. 196). He has been talking about the change in visual experience that results from seeing the solution of a puzzle picture in which the outline of a human being is concealed in a drawing of tree branches. He points out that this solution can’t be represented by the production of an exactly drawn copy, which of course would be invariant between both seeing and failing to see the solution of the puzzle. He goes on: And above all do not say “After all my visual impression isn’t the drawing; it is this—— which I can’t shew to anyone.” — Of course it is not the drawing, but neither is it anything of the same category, which I carry within myself. The concept of the ‘inner picture’ is misleading, for this concept uses the ‘outer picture’ as a model; and yet the uses of the words for these concepts are no more like one another than the uses of ‘numeral’ and ‘number’. If you put the ‘organization’ of a visual impression on a level with colours and shapes, you are proceeding from the idea of the visual impression as an inner object. If something is an ‘inner picture’, then, I can’t show it to anyone; and this isn’t a contingent inability, like having it locked in box to which one has lost the key. The socalled ‘inner picture’ is accordingly a private object. I’m going to suggest that the notion of the private object has been playing a hidden role in experimental psychology right through the twentieth century, and continues to do so. Wittgenstein’s reflections on these matters are as apt now as they ever were.

13 August 2002/testwitt/frem3

3

I’m going to focus on two examples for illustration. The first is directly connected with the kind of thinking Wittgenstein identifies in the passage I have just quoted. It is the investigation of mental, specifically visual, imagery. 2. Mental Imagery in Psychology The pioneer in mental imagery studies, Roger Shepard, conducted experiments concerning subjects’ reaction times in visualizing rotation of complex pictures with a view to deciding which pictures were of the same object and which weren’t. These studies are conceptually unimpeachable. But others were less careful than Shepard himself; it wasn’t long before his experiments were regularly referred to in terms of ‘image rotation’, even by those sceptical that there was any such phenomenon.2 The private object, once banished by behaviourism, was scientifically respectable again. Let’s look at a typical case. Perhaps the best-known psychologist working on mental imagery in recent years is Stephen Kosslyn. Taking his inspiration from a careless interpretation of Shepard’s experiments, Kosslyn defends a so-called pictorialist theory of how mental images are represented in the brain. This theory describes visualizing in terms of inspection of conceptually uninterpreted items held in a visual buffer. This is how Kosslyn and his collaborators describe an experimental procedure whose results are meant to count as evidence in favour of his theory (italics mine): In another experiment, people first learned to draw a map with a mythical island that contained seven objects (e.g., a hut, tree, rock). These objects were located so that each of the 21 interobject distances was at least 1/2 cm. longer than the next shortest [sc. ‘longest’]. After learning to draw the map, subjects were asked to image it and to focus mentally on a given location (each location was used as a focus point equally often). Following this, a probe word was presented; half the time this word named an object on the map, and half the time it did not. On hearing the word, the subjects were to look for the object on their images. If it was present, they were to scan to it and push a button upon arriving at it. If it was not found on the imaged map, they were to push another button. As before, the longer the distance, the more scanning time was needed.3 Here, the experimenters give the impression that their theoretical expectations have been built into the experimental instructions. As we just saw, Kosslyn says that subjects were instructed to ‘look for the object on their images’. This is priming the subjects to report their experiences in question-begging ways. The summary they give here does not of course give the exact words of those instructions, and one might think that perhaps it doesn’t do justice to their own procedures. But the original report inspires no more confidence than this summary (see Kosslyn et al. 1978, pp. 51-2). The point may be put like this. Kosslyn says that subjects reported in their own words experience of ‘a quasi-pictorial image’. But where did they learn to speak in this way? Psychologists’ experimental subjects are very often students of psychology, who, as they tell me themselves, are trained to respond in accepted formats with the threat of 2

3

For example, Nigel Thomas describes Shepard, Cooper et al.’s rather unfortunately titled Mental Images and their Transformations in terms of ‘image rotation’ (Thomas 1997/2001, bibliography), and Peter Slezak follows suit when discussing Kosslyn’s work (Slezak 1995, p. 240 et passim). Kosslyn et al., 1979, p. 136.

13 August 2002/testwitt/frem3

4

academic sanction if they do not comply. We must remember that the aim of Kosslyn et al. was to provide evidence in favour of a pictorial account of visual imagery in which the images are conceptually uninterpreted items held in a visual buffer. For them even to give the impression of having given their subjects the tendentious instruction ‘to look for the object on their images’ and then, if they found it, ‘to scan to it’ is to invite scepticism about Kosslyn’s description of the outcome as ‘the quasi-pictorial image people report experiencing’ (Kosslyn et al. 1979, p. 133). For if these are the instructions the subjects get, it’s not surprising that they report quasi-pictorial images.4 ‘Great pains are usually taken, today, to ensure that subjects in psychological experiments have no idea what hypothesis the experiment is supposed to be testing’, says Nigel Thomas in his article on mental imagery in The Stanford Encyclopedia of Philosophy. Doubtless this is true. But if the hypothesis is built into the language of instruction, the pains will be insufficient. This is just the sort of problem which infected Galton’s imagery questionnaires of 1880, where he asked, for instance, ‘Is the image dim or clear? Is its brightness comparable to that of the actual scene?’5 To sum up: Kosslyn’s instructions work in terms of images which their possessors can study and scan. These instructions present the image implicitly to the subjects, and explicitly to us, as an inner picture, a “conceptually uninterpreted” item which possesses its own geometrical and non-representational properties; in other words, as a kind of object. The subjects are to take a standpoint of observation towards this object and its properties, a standpoint which allows for discovery and surprise at what they find. But this is to beg the question in favour of Kosslyn’s own pictorialist theory. To see that this summary doesn’t reflect an idiosyncratic aberration on Kosslyn’s part but is in the important respects typical of the pictorialist view of imagery, look at these remarks from another prominent pictorialist (Finke 1980, pp. 113, 130): One can think of mental images as being functionally equivalent to physical objects or events. . . . [M]ental images can stimulate visual process mechanisms directly. Thus, when mental images are formed, these mechanisms . . . respond in much the same way as they do when objects and events are observed, resulting in the sensation that an image can be “seen” as if it were an actual object or event. But what if Kosslyn’s experiments had been more carefully conducted and reported, yet the crucial reaction-time data had been the same?6 Then, I think, it would be clearer than it has been that his theory is just one possible explanation among others (such as Pylyshyn’s), and it would be correspondingly harder for pictorialists to pretend that the issue is ‘strictly empirical’ and to condemn rival views as ‘no imagery’ accounts (see, e.g., Finke et al. 1989, p. 54, Kosslyn 1980, p. 35). The impression that the theory is the sole reasonable explanation of the data might never have arisen. But now it is too late: through their uncritical acceptance in Steven Pinker’s book How the Mind Works, Kosslyn’s views have attained the popular status of established scientific results, free from any hint of controversy. Now part of my criticism is that Kosslyn’s procedures suffer from methodological flaws which can be recognized and acknowledged whether 4

5

6

One might have thought that if they had indeed looked for and found it they would already have done any scanning involved. And if they had not, so that scanning was performed as a subsequent exercise, then the differences in reaction times are all too predictable. Quoted by James (1890, p. 51). In case it’s not obvious: Galton is not asking his respondents to compare like with like; one might as well ask whether a small teapot holds less tea than a large picture of a teapot. Tim Crane raised this question in discussion.

13 August 2002/testwitt/frem3

5

or not one agrees with Wittgenstein. But those who do so agree can recognize further that there is a deeper difficulty, one which perhaps disposes experimentalists to be careless with their instructions. It is that, on the pictorialist conception, the mental image is, par excellence, a private object; in the words of Philosophical Investigations page 196, a ‘this—— which I can’t shew to anyone’. That is, even if the methodological flaws had not been present, the pictorialist conception of the image is still vulnerable to the range of difficulties which Wittgenstein assembles in Philosophical Investigations and other works. 3. Introspection, a priori Conviction, and Kinaesthesis Of the various sources of the idea of the private object, the one on which Wittgenstein lays most stress is introspection. It’s this which suggests that the mental image is a sort of inner picture, for instance. But sometimes there’s a conviction that these things just have to be there even when introspection reveals nothing. The conviction is evident in Russell’s famous book Our Knowledge of the External World, in which he sketched his philosophical programme of the logical construction of the external world out of sensedata. Here’s a passage (pp. 84-5) which exhibits the kind of thing Russell’s project involves (italics mine): A table viewed from one place presents a different appearance from that which it presents from another place. This is the language of common sense, but this language already assumes that there is a real table of which we see the appearances. Let us try to state what is known in terms of sensible objects alone, without any element of hypothesis. . . . What we ought to say is that, while we have those muscular and other sensations which make us say we are walking, our visual sensations change in a continuous way . . .. What is really known is a correlation of muscular and other bodily sensations with changes in visual sensations. According to Russell, then, we have primary access to tactile and kinaesthetic data, on the basis of which we can not only say that we are walking but can also begin to construct public space with its real tables from the private spaces, with their visual and tactile tables, of individual perceivers. In view of this metaphysical commitment it’s very striking that Russell doesn’t offer even a tentative way of identifying the ‘muscular and other sensations which make us say we are walking’. He’s convinced, a priori, that they exist in the full diversity and richness required for the logical construction programme. This conviction that kinaesthesis has a rich phenomenology of sensations was shared by William James. Look at what he says: [W]e have, whenever we perform a movement ourselves, . . . kinaesthetic impressions [which] are so many resident effects of the motion. Not only are our muscles supplied with afferent as well as with efferent nerves, but the tendons, the ligaments, the articular surfaces, and the skin about the joints are all sensitive, and, being stretched and squeezed in ways characteristic of each particular movement, give us as many distinctive feelings as there are movements possible to perform.7 (James 1890., p. 488; italics James’s, bold mine) 7

This is a direct parallel of remarks made by Taine about visual perception, quoted with approval by James (1890 p. 48).

13 August 2002/testwitt/frem3

6

And he too thought that these sensations have a kind of priority; not Russell’s metaphysical priority, but an epistemological priority in judgment. We can see this in these remarks on the significance for kinaesthesis of cases like that of Landry’s patient: All these cases, whether spontaneous or experimental, show the absolute need of guiding sensations of some kind for the successful carrying out of a concatenated series of movements. It is, in fact, easy to see that . . . we need to know at each movement just where we are in it, if we are to will intelligently what the next link shall be. (ibid., p. 492; italics James’s) This might be based on introspection. If so, it’s amazing James ever got anything done. But the telling phrase ‘easy to see’ indicates not that he was of an unusually languid disposition but rather that he too was under the compulsion of an a priori conviction. Where does this conviction come from? A major source is something identified by Wittgenstein (Philosophical Investigations, II, viii): “But after all, you must feel it, otherwise you wouldn’t know (without looking) how your finger was moving.” This “quotation” from one of Wittgenstein’s imagined interlocutors condenses what I’ll call the a priori argument: kinaesthetic sensations must exist, because otherwise we wouldn’t possess kinaesthetic ability, that is, the ability to do various things such as describe one’s own posture and movements, obey instructions concerning them, or adopt postures and make movements which are appropriate to one’s situation, all of these without getting outside help or looking. While the possession of this ability by people and animals is undeniable, its explanation in terms of sensations is not. In both the metaphysical and the psychological cases, kinaesthetic sensations are assumed to have two kinds of priority. First, they’re ontologically and epistemically prior to the objects of public space. Secondly, they’re prior to kinaesthetic ability, since they’re supposed to explain it. Both priorities are condensed in another mock-quotation with which Wittgenstein opens his critical discussion of the topic in section viii of Part II of Philosophical Investigations: “My kinaesthetic sensations advise me of the movement and position of my limbs.” Call this the doctrine of kinaesthetic sensations. It isn’t merely the weak claim that there are bodily sensations associated with postures and movements, nor the stronger claim that there are sensations of postures and movements. It’s the very strong claim that these sensations play the two roles specified in the doctrine; that is, that they underpin our kinaesthetic ability and give us private information concerning the state of objects in public space. From now on I’ll use the phrase ‘kinaesthetic sensations’ as definitionally connected with the occupation of these two roles. The view that kinaesthesis has a rich phenomenology is a curious one for those who use the a priori argument; one would think that such a phenomenology renders the argument superfluous. How do we explain this odd combination? The explanation lies in an empiricist assumption which James and Russell shared with Wilhelm Wundt, who had this to say about kinaesthesis (italics mine):

13 August 2002/testwitt/frem3

7

For sensations are, as we know, the only means by which we receive intimation of changes, whether outside of us or within our own body. Now, if we attend closely to our movements, we become aware that they are, in fact, always attended by sensations from the muscles.8 (Wundt 1892, pp. 134-5) The first sentence’s empiricist assumption — that all empirical knowledge rests on sensation — too looks as though it may render superfluous the a priori argument, which is concerned with the basis of kinaesthetic ability. But the second sentence shows why the argument is not superfluous: Wundt, like many later psychologists, holds that in the case of kinaesthesis the sensations must be searched for. The reason Wundt is forced into invoking an a priori argument to boost the empiricist assumption is the notorious recessiveness of kinaesthetic awareness, a recessiveness which might otherwise lead one to question the assumption; and the a priori argument in turn is plausible only given the assumption that the sensations are merely elusive, not absent, and can be found. Look how he goes on: As a rule, it is true, these sensations are so weak that they escape our notice. . . . [W]e require special experimental methods, or an unusual intensity of sensation, if we are to become conscious of it as such. (loc.cit.) Such appeals to ‘special experimental methods’ can be found in textbooks of psychology spanning eight or nine decades. They usually involve the deprivation argument, which is wheeled on whenever uneasiness is felt about the unnoticeability of the supposed rich phenomenology of kinaesthesis. The deprivation argument is simply this: any scepticism about kinaesthetic sensations can be allayed by pointing out that subjects’ kinaesthetic abilities are badly affected when the sensations are missing. There are two versions of this argument in the literature: since things go badly wrong when they are missing, kinaesthetic sensations must (1) exist or (2) be important.9 Version 1 is clearly question-begging, and hence is usually merely gestured at rather than made explicit. Such gestures are common in a wide range of references to experiments and pathology in the literature. Version 2 isn’t question-begging. But how can experimenters be sure that they’re dealing with cases where kinaesthetic sensations are missing? Well, they do it by examining cases where either there’s known physiological damage or temporary damage is induced by blocks applied to the afferent nerves. But for these investigations to be relevant to a conclusion about the role of kinaesthetic sensations, one needs a further assumption. This is that the function of the relevant afferent neural structures in muscles, joints etc. is the transmission of kinaesthetic sensations; and it plays a part in assessing the experimental outcomes by its underpinning a related and directly relevant argument. This argument, in contrast to the near-ubiquitous deprivation argument which relies on it, is almost never formulated but lurks behind the text. It says: despite 8

9

This is not the only matter in which the empiricist assumption influences Wundt’s thinking. It explains, too, his idea that in voluntary action there is a feeling of innervation. For Wittgenstein’s comments on this, see, e.g., Zettel §597, and page 35 of Geach’s notes, pages 157 and 202-3 of Shah’s, and page 278 of Jackson’s, in Geach, Shah, and Jackson 1988. The deprivation argument, usually in its second version, is abundant in the literature. Examples include James 1890 p. 490, Külpe 1893 p. 141, Royce 1903 pp. 126-7, Krech and Crutchfield 1958 p. 73, Darley et al. 1984 p. 96, and Coon 1986 p. 101.

13 August 2002/testwitt/frem3

8

their elusiveness in consciousness, kinaesthetic sensations must exist because the appropriate physiological apparatus is present.10 Let me sum up what I’ve been saying about the sources of the idea that our kinaesthetic ability rests upon our monitoring of our kinaesthetic sensations. The crucial propositions which underpin the doctrine of kinaesthetic sensations are essentially a priori dogmas, not empirical discoveries. No wonder that the doctrine seemed obvious. And again, no wonder that these dogmas provide much of the material for Wittgenstein’s two extended discussions, the enigmatic section viii of Part II of Philosophical Investigations and the more approachable §§382-407 of Remarks on the Philosophy of Psychology Volume I (hereafter referred to as ‘RPP’). Both these contain more or less direct criticisms of the various arguments and assumptions I’ve identified here, and others that I’ve omitted. 4. Kinaesthetic Sensations in Wittgenstein’s Writings But what has this to do with private objects? Everything. Wittgenstein himself makes the connection most explicitly in RPP, I, §393, which begins: But isn’t there such a thing as a kind of private ostensive definition for feelings of movement and the like? E.g. I crook a finger and note the sensation. And much of his discussion of kinaesthesis in RPP is concerned with the kind of ontological and epistemic priority that I identified as presupposed in the treatment of kinaesthesis by Russell and by James and other psychologists both of that era and later. He is, for instance, especially critical of the idea that kinaesthesis has the rich phenomenology which is required to make the priority claims even plausible. The connection with privacy is characteristically obscured in Wittgenstein’s far more elusive discussion in Philosophical Investigations, where the explicit discursiveness characteristic of RPP has disappeared in the process of selection from and refinement of his earlier manuscripts. Nevertheless, it emerges in the middle of his discussion when he suddenly asks the surprising question, What is the criterion for my learning the shape and colour of an object from a sense-impression? [The original German has no explicit counterpart to the phrase ‘of an object’.] The general theme of the discussion which follows is that where a sensation offers a genuine basis for a judgment about how things are in the world, the sensation must be characterizable independently of the things the world contains. This condenses a good deal of fairly rambling material from RPP. The point of it is not so much that kinaesthesis is not a matter of sensations; rather it is that, even if it were, it would still be the wreck of Russell’s logical construction programme, since those sensations couldn’t serve as the programme’s data, that is, in the way required by the doctrine of kinaesthetic sensations.11 Incidentally, and in the light of Russell’s insouciant assumption that the kinaesthetic data exist in the required form, it is a striking fact that those philosophers prominent in the recent debates over consciousness, who argue for the existence of qualia, never consider kinaesthetic qualia. When detail is called for, they 10

11

This “physiological” argument is usually found in company with the deprivation argument. For some sources, see footnote 9. Wittgenstein brings this out very clearly at RPP, I, §§401-2.

13 August 2002/testwitt/frem3

9

confine themselves almost exclusively to vision. It would be interesting to see an attempt to reproduce, in the modes of perception appropriate to human movement, the arguments depending on absent or inverted qualia. We know that Wittgenstein was interested enough in psychology to pursue experimental research in it at one stage; and we know too that he was interested enough in Russell’s metaphysics and James’s philosophy of mind to make them constant targets of his critical scrutiny. With this topic, the various interests converge, and connect with his running discussion of privacy. 5. Private Objects Again This brings us back to the notion of the private object. Prominent among Wittgenstein’s targets of criticism is the idea that the kinaesthetic sensation is somehow prior in the ways that Russell and various psychologists have supposed. This is the idea that they are among the building blocks in a logical construction of the external world; or they provide a basis from which we can tell the position and movements of our own bodies. Both these ways require the sensations to be identifiable independently of the bodily states for which they are supposed to be evidence or criteria. Likewise, visual images, on the pictorialist account favoured by some experimental psychologists, should be identifiable independently of what they are images of. And Wittgenstein is constantly querying this independent identifiability of the supposed inner objects. Yet without it they cannot be said to be private objects, things which I can observe for myself but cannot show to anyone else. There is, however, a curious contrast between the ways in which these two kinds of private objects now figure in experimental psychology. Although I haven’t demonstrated it here, it’s clear from the literature that the doctrine of kinaesthetic sensations is nowadays a shadow of its former vigorous self: experimenters now rarely appeal to it, and it lingers mainly in the text books. But the decline of the doctrine of kinaesthetic sensations has been paralleled by the rise of the pictorialist account of visual imagery. It’s as though psychology, like philosophy, can never entirely resist the appeal of the idea of the immediate contents of consciousness. Stewart Candlish The University of Western Australia [email protected]

13 August 2002/testwitt/frem3

10

REFERENCES The cited date is that of original publication. Where this differs from the cited edition, a separate date for the latter is shown. Block, N. (ed.) 1981

Imagery (Cambridge, MA & London: MIT)

Candlish, S. 1996/1998

‘Private Language’, The Stanford Encyclopedia of Philosophy, ed. Edward N. Zalta (Stanford, CA: CSLI, Stanford University). [http://plato.stanford.edu/entries/private-language/]

Coon, D. 1986

Introduction to Psychology, 5th edition (St Paul: West Publishing Company)

Darley, J., Glucksberg, S.,Kamin, L. & Kinchla, R. 1984 Psychology, 2nd edition (Englewood Cliffs, NJ: Prentice-Hall) Finke, R. 1980 Finke, R., Pinker, S. & Farah, M. 1989 Geach, P., Shah, K. & Jackson, A.C., 1988

‘Levels of equivalence in imagery and perception’, Psychological Review, 87: 113-32 ‘Reinterpreting visual patterns in mental imagery’, Cognitive Science, 13: 51-78 Wittgenstein’s Lectures on Philosophical Psychology 1946-47, (Hertfordshire: Harvester)

James, W. 1890

The Principles of Psychology (New York: Henry Holt), Vol. 2

Kosslyn, S. 1980

Image and Mind (Cambridge, MA: Harvard University Press)

Kosslyn, S., Ball T. & Reiser, B. 1978

‘Visual images preserve metric spatial information: evidence from studies of image scanning’, Journal of Experimental Psychology: Human Perception and Performance, 4: 47-60

Kosslyn, S., Pinker, S., Smith, G. & Schwartz, S. 1979 ‘On the demystification of mental imagery’, The Behavioral and Brain Sciences, 2, 535-48, partly reprinted in Block (ed.), 1981: 131-50; page references here are to the reprint Krech, D. and Crutchfield R. 1958

Elements of Psychology (New York: Knopf)

Külpe, O. 1893

Outlines of Psychology, trans. Titchener (London: Swan Sonnenschein, 1909; original German publication 1893)

Morgan, C. 1961

Introduction to Psychology, 2nd edition (New York: McGrawHill)

Pinker, S. 1997

How the Mind Works (London: Allen Lane)

Pylyshyn, Z. 1981

‘The imagery debate: analog media versus tacit knowledge’, Psychological Review, 88: 16-45

——, Z. 1984

Computation and Cognition (Cambridge, MA: MIT)

Royce, J. 1903

Outlines of Psychology (London: Macmillan)

13 August 2002/testwitt/frem3

11

Russell, B. 1914

Our Knowledge of the External World (London: Allen and Unwin)

Shepard, R. 1978

‘The mental image’, American Psychologist, 33: 125-37

Shepard, R.N., Cooper, L.A., et al. 1982

Mental Images and Their Transformations (Cambridge, MA: MIT)

Shepard, R. & Metzler, J. 1971

‘Mental rotation of three-dimensional objects’, Science, 171: 701-3

Slezak, P. 1992

‘When can visual images be re-interpreted? Non-chronometric tests of pictorialism.’, Proceedings of the Fourteenth Annual Conference of the Cognitive Science Society (Hillsdale, N.J.: Laurence Erlbaum Associates)

—— 1995

‘The “philosophical” case against visual imagery’, Perspectives on Cognitive Science, ed. P. Slezak, T. Caelli and R. Clark (Norwood, NJ: Ablex)

Thomas, N. 1997/2001

‘Mental imagery’, The Stanford Encyclopedia of Philosophy, ed. Edward N. Zalta (Stanford, CA: CSLI, Stanford University). [http://plato.stanford.edu/entries/mental-imagery/]

Tye, M. 1991

The Imagery Debate (Cambridge, MA: MIT)

Wittgenstein, L. 1953

Philosophical Investigations (Oxford: Basil Blackwell)

—— 1967

Zettel (Oxford: Basil Blackwell)

—— 1980

Remarks on the Philosophy of Psychology [RPP] (Oxford: Basil Blackwell), 2 vols

Wundt, W. 1892

Lectures on Human and Animal Psychology, trans. J. E. Creighton and E. B. Titchener (London: George Allen & Co., 1912; original German publication Leipzig, 1892)