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The Georgicks of Virgil, with an English Translation and Notes Virgil, John Martyn Ipsi in defossis specubus secura sub alta Otia agunt terra, congestaque robora, Pierius says it is confecto in the Roman manuscript. And Tacitus also says the Germans used to make caves to defend them from the severity of winter, .

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The passages just cited and others like them perhaps imply no more than that Hume thought of ideas as quasi-perceptual experiences a conclusion that Yolton might be able to accept , but the fact that Hume approvingly repeats Berkeley's argument against general ideas Treatise I. This is also suggested by his choice of the word 'impression' to designate the percepts of which ideas are the images or copies.

Clearly the word alludes to the wax impression model of perception and memory that we find in Plato and Aristotle, and although Hume, no doubt, does not intend it to be understood too literally, the fact that he thinks it an appropriate and innocuous metaphor remains telling. Reid is not saying that we do not have quasi-perceptual experiences, but he wants to deny that these are caused by representational mental entities that we experience in lieu of some actually present physical object or scene. However, images still have a significant role to play in his account of how our concepts connect to empirical reality.

The imagination einbildungskraft must synthesize the inchoate deliverances of the senses, the sensory manifold, into a coherent, meaningful image, a true representation that the understanding can grasp and bring under some concept. Unfortunately, Kant was unable to give a satisfactory account of how the imagination, even in concert with the understanding, can achieve this. Unfortunately, however,. Thus Kant, in attempting to grapple with problems about the nature of mental representation that the Empiricists had failed to solve, left the process of image formation, and the nature of the image itself, deeply mysterious.

When psychology first began to emerge as an experimental science, in the philosophy departments of the German universities in the late 19th century, and soon after in the United States, the central role of imagery in mental life was not in question. For these pioneering experimentalists, such as Wilhelm Wundt in Germany and William James in America, mental images often, following the established usage of the Empiricist philosophical tradition, referred to as ideas held just the same central place in the explanation of cognition that they had held for philosophical psychologists of earlier times.

Edward B. Titchener, a student of Wundt who established himself as a leading figure in American psychology, was particularly interested in imagery, and an experiment performed by one of his students, C. Perky, has become particularly well known. It is often assumed that it shows that there is no qualitative experiential difference between mental images and percepts, but further experimental investigations have raised some doubts about this conclusion see Supplement: The Perky Experiment.

However, developments within psychology at the beginning of the 20th century began to cast doubt on this long established consensus. Their results were challenged on several grounds by Wundt, Titchener and others, and were certainly never definitively established. Nevertheless, the bitter dispute that ensued, the so called imageless thought controversy, had a profound effect on the development of scientific psychology and, very arguably, philosophy too.

Most psychologists became, in effect, profoundly disillusioned with the whole notion of mental imagery, and either avoided seriously considering the topic, treated it dismissively, or, in some extreme cases, denied the existence of the phenomenon outright. These attitudes noticeably influenced other disciplines, including philosophy. Although the psychological study of imagery revived with the rise of cognitivism in the s and 70s, when new experimental techniques were developed that enabled a truly experimental study of the phenomenon, current views about, and attitudes towards, mental imagery cannot be properly understood without an awareness of this history, versions of which, of varying degrees of accuracy, have passed into the folklore of psychology.

The following supplements discuss ideas and research about imagery in early late 19th and early 20th century scientific psychology:. Supplement: Edward B. Titchener: The Complete Iconophile. He and his students there developed a direct challenge to the prevalent imagery theory of thought. In , two of these students, Mayer and Orth, performed a word association experiment in which subjects were asked to report everything that had passed through their mind between hearing the stimulus word and giving the response. Note that it was normal practice, in this era of psychology, for experimental subjects, or observers as they were more often called, to be drawn from among fellow researchers within the same laboratory, often including the supervising professor.

Present day psychologists would, with good reason, suspect such subjects of being liable to produce results strongly biased by theoretical preconceptions Orne, ; Intons-Peterson, 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. In however, it was thought that experienced and knowledgeable observers were more likely to produce consistent and meaningful results than the psychologically untrained.

In the case of the Meyer and Orth experiment, two amongst the four subjects were Meyer and Orth themselves. Nevertheless, they professed to be surprised by some of their findings. In particular:. Unsurprisingly, Wundt, and others, refused to accept these new methods and conclusions, and a heated debate, the so called imageless thought controversy, ensued.

Though Wundt was surely skeptical of the existence of imageless thoughts, his primary criticisms were methodological. He was very much concerned with the fact that the experiments were necessarily constructed so that the introspective reports were given after the completion of the experimental task word association, sentence interpretation, or whatever. Such experiments, Wundt argued, were open invitations to suggestion, and, indeed, were. Titchener see supplement also strongly objected to the alleged demonstrations of imageless thought, but for different reasons. Titchener suggested that the purported bewusstseinslagen etc.

Instead, they found the fleeting imagery or the subtle bodily sensations that Professor Titchener's theory predicted Titchener, ; Humphrey, This work of Titchener's like other responses to the imageless thought controversy from America, Britain, and elsewhere had relatively little impact in Germany, which, with some justification at that time, still regarded itself as very much preeminent in psychological science. Nevertheless, on both sides of the Atlantic the controversy was recognized as touching on deep foundational issues in the science of mind.

Although largely forgotten today, it seems to have had a lasting impact on the development not only of psychology, but philosophy as well. Many psychologists and philosophers of this era came, partly for this reason, to feel that thought should be understood in terms of language per se , and that it was a serious mistake ever to have believed that the representational power of language derives from some more fundamental form of representation, such as mental imagery.

But the imageless thought controversy was never satisfactorily resolved, at least in the terms in which it was originally posed. Indeed, philosophers are still arguing over the issues involved e. The irresolvable dispute contributed significantly to a growing sense of intellectual crisis within psychology, leading to a deep loss of confidence persisting to the present — see Schwitzgebel a,b, in the scientific value of introspection.

It also led to a precipitous decline in scientific interest in imagery, especially in the United States after the Behaviorist movement took hold. On the one hand its importance in the cognitive economy or even its very existence was now subject to doubt; on the other hand it had come to seem that it was very difficult, if not impossible, to study it experimentally and objectively. By the early 20th century, particularly in the United States, where it most flourished, psychology had progressively established a disciplinary identity distinct from the parent discipline of philosophy.

However, interest in and attitudes towards imagery amongst philosophers followed a very similar trajectory to that seen in psychology. Images, he pointed out, are subjective and idiosyncratic, whereas word meanings are objective and universal. Today, it is largely thanks to Wittgenstein's efforts that,. Many other remarks and arguments scattered through Wittgenstein's other posthumously published writings, particularly in Zettel , the Remarks on the Philosophy of Psychology a, b , and the Last Writings on the Philosophy of Psychology , demonstrate that he was fascinated by imagery, but deeply skeptical not only about the large cognitive role traditionally assigned to it, but also about the traditional understanding of the image as a sort of inner picture see, e.

No-one could seriously doubt that Wittgenstein himself recognized the experiential reality and philosophical importance of imagery: he expends so much effort wrestling with the concept. Instead, Wittgenstein regarded language itself as the preeminent vehicle of thought, and he held that the meanings of linguistic expressions arise from the various uses to which they are put.

He thus saw no need and no room for language to be semantically grounded in any other form of representation. In support of this position, he strove to show that imagery the only real candidate for the job could not possibly be the semantic ground of language, and he is very widely believed to have succeeded. The two themes of the cognitive unimportance of imagery and its non-pictorial nature were taken up, and argued more fully, by numerous post-Wittgensteinian philosophers in the latter half of the twentieth century. Although there may be some tension between the themes most arguments against the imagery theory of thought and meaning seem to turn upon mental images being, in some sense, picture-like in practice they have rarely, if ever, come into conflict; rather, both have played their part in setting the iconophobic tone of the era.

Philosophers such as Harrison —3 , Goodman , and Fodor have reinforced, restated and extended Wittgenstein's arguments for the irrelevance of imagery to semantics, and have made a powerful and influential case. One point that is often made is that there seems to be no natural way of representing certain linguistically expressible concepts in an image. Logical relations are often mentioned in this context. It is hard to see, for example, how it might be possible to form a mental image of not is any image in which John does not appear an image of John is not here? The image theory of linguistic meaning might seem to be on its strongest ground when it is applied to nouns or, at least, concrete nouns.

On the face of things, it is plausible to think that one understands the meaning of the word 'dog' if and only if as the word is able to arouse an image of a dog in one's mind. Berkeley's argument against general ideas had long brought this simple picture into question, however see section 2. Can my mental picture of a dog represent any dog, or dogs in general, or is it, at best, just a representation of Rover? Twentieth century philosophers, however, would soon point to an even deeper problem.

They assumed, probably often correctly, that the traditional image theory of meaning was based upon the assumption that images themselves get their meaning through resembling their objects: an image of a dog represents a dog because it resembles or looks like a dog, in the same way that a painting of Queen Elizabeth represents Queen Elizabeth because it looks like her.

This resemblance theory of representation is not always explicitly stated by image theorists of thought and language perhaps it is thought to be too obvious to be worth saying, or perhaps not all of them are really committed to it , but Russell , , for one, explicitly takes the view that words represent because they are associated with mental images, and that the images themselves represent because they resemble their objects.

This resemblance theory became the main focus of attack. Consider a photograph of Leo the lion. It would certainly be reasonable to say both that it resembles and that it represents him. But now suppose we have two such photographs. Each photo resembles the other more than either resemble Leo both photos are small, rectangular pieces of card, with a white border around a gray or vari-colored rectangle, and neither is carnivorous or furry , yet we would normally want to say that they each represent Leo, and not that they represent each other.

Of course, a photograph of Leo does resemble him, when the right aspects of resemblance are considered, but in this regard Leo equally resembles the photograph. We are unlikely, however, to want to say that he represents the photo. Resemblance is a symmetrical relationship, and representation is not. None of this necessarily means that resemblance never plays any role in representation, but in order for it to do so, the relevant aspects of resemblance have to be recognized, and the resembling object has to be used or, at least, taken as a representation.

But surely, before a cognitive system can recognize or use the relevant aspects of resemblance between a photograph or an inner quasi-picture and an object or a percept , it must already be able to represent the picture and its object, and their various features, to itself. The mind's power to recognize resemblance seemingly depends on its power to represent things, rather than vice-versa. On grounds such as this, Goodman argued that even physical pictures — paintings drawings, photographs, etc.

Clearly the argument applies to mental pictures quite as much as to physical ones. Goodman, A mental image of John, who is a tall fat man, might mean John , it might mean fat man or John is a fat man , or tall man , or just man , human being , or even physical object. On the other hand it might mean John in just the particular pose and situation in which he is imagined.

After all, it resembles all those things and indefinitely many more. What an image means, according to Fodor, what it is an image of , will necessarily remain radically indeterminate unless it is pinned down by an associated linguistic description. On either view, though, the traditional semantic dependency is inverted. Instead of the meaningfulness of language being grounded in imagery, the meaningfulness of imagery seems to need grounding in some sort of language. Arguments against the pictorial nature of imagery, which are scarcely more than hinted at in Wittgenstein's published works, were developed much more explicitly by Ryle Other philosophers influenced by both Wittgenstein and Ryle soon carried forward this critique of the inner picture: Shorter and Dennett in some respects anticipating the work of Pylyshyn — see section 4.

Although expressed in very different terms, Ishiguro's position on imagery is not altogether unlike the view developed earlier in the century by Sartre See Ryle for an interesting comparison of his own views about the mental, including mental imagery, to views in the phenomenological tradition, to which Sartre belonged. Under the influence of Husserl rather than Wittgenstein, Sartre also stressed the intentionality of imagery and denied that mental images conceived as entities exist:.

It is important to be clear that just because Sartre and Ryle, Shorter, Ishiguro, and others hold that mental images are not inner pictures, nor even, indeed, any sort of entity, they are not thereby denying that people have quasi-perceptual experiences, or even that these may sometimes be very vivid. Unfortunately, perhaps because the notion that such experiences are caused by inner pictures is so entrenched in our folk psychology, this point does not always seem to have been clear to critics of such views, and it has even been occasionally suggested that they could not possibly be held by anyone personally familiar with the experience of imagery.

By contrast, in his Mental Images — A Defence , Hannay vigorously championed the reality of inner pictures see also Hannay, , and for a counterargument see Candlish, But, despite the fact that he had no thought of reinstating imagery to its traditional importance in cognitive and semantic theory, Hannay clearly saw himself in as a lonely dissenter, a voice crying in the wilderness against philosophy's virtually monolithic iconophobic consensus.

In the subsequent decades that consensus has been fractured, but by no means shattered, by developments in cognitive psychology and cognitive science discussed below. In particular, in the wake of Kosslyn's , seminal work on the cognitive psychology of imagery, a growing number of philosophers are now ready to defend the reality of mental pictures, and show no sign whatsoever of feeling embattled e. Many other philosophers, even if not entirely convinced about pictures, now take a serious interest in the cognitive science of imagery.

Nonetheless, the post-Wittgensteinian consensus that imagery cannot be as important as it once seemed to be, that it cannot be the ground of linguistic meaning or the prime vehicle of thought, remains strong. Despite all that has happened in cognitive science, imagery has by no means regained its former prominence in philosophy. A revival of interest in imagery was an important component of the so called cognitive revolution in psychology during the s and early s, a period when the Behaviorist intellectual hegemony over the field was broken and the concept of mental representation was established as central and vital to psychological theorizing Baars, ; Gardner, ; but see also Leahey, Although the emergence of computational models of mental processes probably played the leading role in the rise of cognitive psychology and cognitive science, the new interest in imagery was independently motivated, and contributed significantly to the growing feeling, amongst psychologists, that both the ontology and methodology of Behaviorism were excessively restrictive, and that inner mental processes and representations could, after all, be useful, or even indispensible, scientific concepts.

Quite apart from the broader talk of revolution in psychology in this era e. Holt indicates a number of developments that began to lead some psychologists, in the s, to begin to pay significant attention to imagery again. These include research on hallucinogenic drugs, developments in electroencephalography, the discovery of REM sleep and its correlation with dreaming, and Penfield's finding that direct electrical stimulation of certain brain areas can give rise to vivid memory or pseudo-memory imagery. More significant, however, according to Holt was a line of psychological research that was originally inspired by practical, rather than theoretical, concerns: by the perceptual problems experienced by people such as radar operators, long-distance truck drivers, and jet pilots, whose work requires them to remain perceptually alert whilst watching monotonous, impoverished, and barely changing visual stimuli over extended periods of time.

Despite the introspective nature of the evidence, the practical implications of these findings for such things as road and air safety made them hard to dismiss. Beginning in the s, and perhaps stimulated by some of the research mentioned by Holt, there was also a growing interest in the application of imagery based techniques in psychotherapy and psychosomatic medicine see, e. A journal dedicated to the subject, the Journal of Imagery Research in Sport and Physical Activity commenced online publication in Great claims are also made, by some, for the healing powers of guided imagery , whereby clients or patients are encouraged to visualize particular scenes or scenarios thought to have therapeutic value e.

Guided imagery techniques have been claimed to be effective for purposes ranging from chronic pain relief and the preparation of patients for surgery Fontaine, ; Tusek et al. It is sometimes claimed or implied that these sorts of techniques are based upon ancient oriental, and particularly Indian, spiritual practices e. The journal publishes articles on imagery from a wide range of psychological perspectives, including the cognitive.

Its journal, Imagination, Cognition and Personality , commenced publication in the early s. The Association may now be defunct — its web site has disappeared — but the journal continues to be published. Despite the developments outlined above, interest in imagery amongst experimental psychologists remained at a fairly low level until the mid to late s.

It was the recognition, in that period, of the powerful mnemonic effects of imagery that changed the situation, leading to a thriving tradition of experimental research, and securing imagery a firm place in cognitive theory. These mnemonic effects, it turned out, could be clearly demonstrated in readily repeatable experiments that did not rely in any way upon introspective reports. According to Bugelski , , an important stimulus to the flowering of experimental research on imagery and memory [ 23 ] was the publication of Frances Yates' celebrated and widely read historical study, The Art of Memory.

Yates details how imagery based mnemonic techniques, particularly versions of the so-called method of loci , were in widespread use amongst European intellectuals, educators, and orators from classical Greek through to early modern times, and she argues that the knowledge and use of these techniques may have had quite significant effects on the development of Western philosophical, theological, and early scientific thought. Shereshevskii's truly prodigious feats of memory were apparently made possible by an abnormally vivid visual imagination, often harnessed to his own version of the method of loci.

Turner had formerly worked as a stage magician and memory man, and suggested that the subjects be taught an imagery mnemonic technique to help them to realize the full potential of their memories. As a result, however, the experiment was deemed a failure; when the subjects used the mnemonic technique, there seemed to be no practicably measurable limits to their information-storage capacity! Because of this, the study was never published, but word of the findings does seem to have got out, particularly via Eugene Galanter, who had also been at the University of Pennsylvania at the time.

This book is considered one of the key, foundational works of the cognitive revolution in psychology, and was enormously influential in the field although it is better known for its introduction of concepts from computing and Artificial Intelligence research into psychology, rather than for its account of imagery mnemonics Gardner, ; Hirst, ; Galanter, ; Neisser, p.


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But, almost certainly, the most important figure in the study of the mnemonic effects of imagery was the Canadian psychologist Allan Paivio, whose interest in the subject seems to have originated quite independently of any of the influences mentioned so far, going right back to , when he witnessed an impressive demonstration of the power of an imagery mnemonic, and was taught how to use it, as part of a course on public speaking that he attended Paivio, c, pp. The connection between imagery mnemonics and public speaking goes right back to their origins in ancient times: see Supplement: Ancient Imagery Mnemonics.

Despite this, perhaps because of the still generally iconophobic character of North American psychology through the s see Supplement: The American Response: Behaviorist Iconophobia and Motor Theories of Imagery , his first publication to very tentatively suggest a role for imagery in memory did not appear until Paivio, The former debate is about the function of imagery in cognition, the latter is about the nature and mechanism of imagery itself.

The findings of this extensive experimental research program on the mnemonic effects of imagery, can be crudely summarized as the discovery of two principal effects. Secondly, and somewhat more controversially, Paivio and others claim to have shown that imagery plays a large role in verbal memory even when the experimental subjects are not given explicit instructions to form imagery, and make no deliberate effort to do so. Once these quantitative imagery values were established, Paivio was able to show, in various experimental designs, that words with high imagery values were consistently remembered significantly better than those with lower ones, quite regardless of any conscious intent on the subjects' part to form relevant images Paivio, , , a.

By the end of the s, the work of Paivio and others on the mnemonic properties of imagery had established a strong empirical case for the functional importance of imagery in cognition. The phenomenon could no longer be ignored by psychologists, or treated as a mere subjective epiphenomenon of no scientific interest, as it had been in the Behaviorist era. However, this work had done very little to illuminate the nature of imagery itself, or of the cognitive mechanisms that generate it. Kosslyn also demonstrated that the subjective sizes of visual mental images and the relative sizes of their sub-parts measurably affect the times it takes to inspect and report on particular details of imagined objects.

The presence of larger features of an object could be reported more quickly from an image of the object than smaller features. As this size-time relation, did not appear unless the subjects used imagery to do the task i. It should be noted that the methodology of many of these experiments leaves them vulnerable to the charge, pressed by several critics, that the results reflect not so much the normal workings of cognition, and the properties of the representational structures such as mental images that enable them, but, rather, what psychologists call the demand characteristics of the experimental situation Orne, ; Rosnow, see supplement.

This is a well-known pitfall of psychological experimentation with human subjects, and experimenters are, for the most part, well aware of it, and take what precautions they can to rule out the possibility that demand characteristics might significantly influence their findings. Nevertheless, certain types of imagery experiment, including most of those discussed in this section, appear to be particularly susceptible to such influence Intons-Peterson, , and it may sometimes be effectively impossible to rule out the possibility that demand characteristics have played a large, or even predominant, role in determining the results.

Thus, some of the results obtained in this area of research remain open to question. On the other hand, converging evidence from several different types of experiment seems to have been enough to establish a consensus amongst most cognitive scientists that the processes of mental scanning, mental rotation, and the size effects in image inspection are real and significant components of cognition.

A lively and high-profile theoretical debate ensued, about the nature of mental imagery and of mental representation in general. The analog-propositional debate , occasionally also called the picture-description debate , or sometimes just the imagery debate as if there were no other debatable or hotly debated issues about imagery is an ongoing and notoriously irreconcilable dispute within cognitive science about the representational format of visual mental imagery. The huge impact it had on the early development of the field appears to have resulted in a widespread belief, amongst both philosophers and cognitive scientists, that analog and propositional theories those terms being understood in the rather special senses that they have acquired in this context , together, perhaps, with hybrid theories that claim to incorporate elements of both e.

That is not the case, as we shall see in section 4. To a first approximation, the analog side of the debate holds that the mental representations that we experience as imagery are, in some important sense, like pictures, with intrinsically spatial representational properties of the sort that pictures have i.

The propositional side, by contrast, holds the relevant mental representations to be more like linguistic descriptions of visual scenes , without inherently spatial properties of their own. Although it began as a dispute amongst scientists, the debate clearly touches on fundamental issues about the nature of mind and thought, and perhaps the nature of science too, so it soon attracted a good deal of interest from philosophers as well. It is good to be aware that the terms analog and propositional, although they have become entrenched usage in this context, are both potentially misleading.

On the one hand the propositions which are supposed by some to constitute the descriptions that constitute imagery, are not really propositions at all in the established philosophical sense of the word: rather they are a sort of sentence albeit not sentences natural language, but of mentalese. Although the debate began, and was at its fiercest, during the formative years of the discipline of cognitive science in the s, it has yet to reach a generally accepted resolution.

However, it may be difficult to understand the scientific and philosophical issues at stake unless one has a sense of the historical and intellectual context in which the dispute originated. Matters became so hotly contested during the s that some participants, most notably Anderson and Palmer b, , came to the conclusion that the disagreement was quite impossible to resolve by the methods of scientific psychology, or perhaps at all. Indeed, Anderson offered a formal proof purporting to show that the two main contending theories are empirically equivalent.

Anderson's arguments in particular aroused much interest at the time, and were themselves vigorously disputed Hayes-Roth, ; Pylyshyn, b; Cohen, and defended Anderson, However, the main debate continued, and it is probably fair to say that most observers have come to the conclusion that the empirical equivalence claimed by Anderson is ultimately not particularly interesting or important. It can probably be regarded as just a special case of the well known Duhem-Quine underdetermination of theory by evidence: many philosophers of science hold that any theory can be made to fit any evidence provided one is allowed freely to supplement the theory with arbitrary and perhaps ad hoc, complex, and implausible auxiliary hypotheses, which is essentially what Anderson was doing.

Nevertheless, the fact that such claims could be seriously proposed and discussed is testament to just how acrimonious and intractable this debate about imagery had come to seem at the time, and how important it was to those involved. The very possibility of a science of cognition seemed to be under threat. Despite this, the debate's focus has, in practice, been quite narrow. Although it is often understood to be a debate about the nature of imagery per se , it may more truly be seen as about what theory of imagery will best account for the facts within the parameters of a computational functionalist theory of the mind , i.

Although this computational functionalism still has many adherents, it no longer dominates the philosophy of mind and cognition to the extent that it once did. However, in the early s it was new and exciting, and the computational approach to cognitive theory that it sanctioned was being taken up with great enthusiasm by many psychologists Baars, ; Gardner, Initially, the concurrent rises of imagery research and computational psychology, through the s and into the s, played mutually reinforcing roles within the cognitivist revolution against Behaviorism, because they both implied that the concept of mental representation should play a central role in the science of the mind.

However, a tension soon became apparent between the symbolic and syntactic concept of mental representation that came from Artificial Intelligence and the, on the face of it, very different concept of representation implicit in the work of the imagery researchers. The analog-propositional debate, and much of the passion and partisanship it aroused, grew out of that tension, and, more particularly, the desire to bring imagery within the fold of computational functionalism. The analog-propositional debate may be said to have begun when this tension found its first clear expression, in a very influential article by Zenon Pylyshyn Although a number of other cognitive scientists and philosophers have taken positions, and made empirical and theoretical arguments, similar to and supportive of those of Pylyshyn e.

In his article he raised a number of objections to this notion, some of which have withstood criticism better than others, but the underlying worry was clearly that the inner-picture theory of imagery inevitably commits the homunculus fallacy: it implicitly relies on the assumption that there is a little man or rather, something that is the functional equivalent of a full-fledged visual system, including eyes , or, at the very least, something with inexplicable mental powers, inside the head to reperceive, experience, and interpret the image. The broad functional architecture of Kosslyn's theory, in fact, closely parallels that of Descartes' account of imagery see section 2.

However, their critics remain unconvinced that they have truly even recognized this pitfall, let alone successfully avoided it Slezak, , ; Thomas, b, , , ; Pylyshyn, a,b, a,b,c, , What the program actually does is construct and display a picture on the computer's screen, on the basis of a stored file, and then move it about on the screen in various ways, in order to model some of the ways in which people can supposedly manipulate their mental images such as in mental rotation and mental scanning.

At the time when the program was written, when computer graphics were in their infancy, and when few people had ever even seen a computer, it may not have been an entirely unimpressive achievement. However, nothing in the program nor, so far as I am aware, in any computer simulation of a pictorial theory of imagery written since implements, or even attempts in any way to simulate or model, a conscious awareness of the pictures. Only the human onlooker consciously experiences the pictures, knows that they are pictures, and can tell what they might be pictures of Thomas, If quasi-pictorial theory were capable of accounting for the representational and conscious nature of imagery without appealing to a homunculus, then the Kosslyn-Shwartz program might constitute a heuristically useful if crude and preliminary model of how images might be built up and transformed.

However, despite vehement claims to the contrary e. In a subsequent paper, Pylyshyn introduced an important new argument against pictorialism, based on the concepts which he introduced of cognitive penetrability and impenetrability. Cognitive processes are said to be cognitively penetrable if their workings can be affected by the beliefs and goals of the person, and cognitively impenetrable if they cannot be.

Figure 4. In both cases, the two horizontal lines are the same length, but appear to be different lengths. If that were the case, imagery should be a cognitively impenetrable phenomenon, but it is not. Not only do we have a large degree of voluntary control over the content of our imagery experiences, but it has also been experimentally demonstrated that extra-visual beliefs can influence the course of supposed imagery processes. For instance, he holds that if subjects are asked to scan their mental gaze from one point to another on a mental image of a map, what they interpret these instructions to be asking them to do is to behave as if they were actually looking at the relevant map and scanning their gaze between the points.

Because they know from their history of ordinary visual experience that it takes longer to scan between points that are further apart, this will be reflected in their performance. Thus, the fact that people instructed to scan across their images take longer to scan longer distances is not evidence of the existence of some inner, mental, image-space.

Rather, it is a reflection of people's implicit understanding which they may not necessarily always be able to articulate of the visual properties of the actual space around them cf, Morgan, Pylyshyn's critics have often been inclined to conflate his tacit knowledge theory with the view that the results of imagery experiments may be fatally contaminated by the effects of experimental demand characteristics see supplement.

However, although he clearly does think experimental demand plays a large role in determining many of the results on imagery, he resists this interpretation of his position. He is not saying as is sometimes implied that experimental subjects are, as it were, consciously faking their performances in order to please the experimenter.

Rather they are doing their best to comply with experimental instructions that turn upon the slippery concept of mental imagery. It is generally assumed that problems caused by demand characteristics can be avoided or minimized by careful and ingenious experimental design, or by such tactics as post-experimental questioning of subjects to see if they have guessed the experimental hypothesis Kosslyn, for one, routinely throws out data from subjects who guess this correctly.

Rather, the problem lies with the basic conceptualization of the phenomena and the experimental tasks by experimenter and subject alike. Of course, Pylyshyn was far from the first person to raise objections to the idea of inner pictures, or to criticize the standard interpretations of imagery experiments. What made his critique particularly effective was that he began, both in his article and in subsequent writings e.

At last, there seemed to be a viable alternative to the pictorial conception of imagery that had dominated folk, philosophical, and psychological thinking about imagery since ancient times. Particularly important for Pylyshyn was the work of Simon and Newell , and their students Baylor and Moran , who had already made some progress in devising symbol systems suitable for the computational representation of the spatial structure of simple layouts or objects such as rectangular blocks.

They explicitly presented these representations as models of the image representations that people use in doing certain visuo-spatial cognitive tasks. In his original article, Pylyshyn alludes to a number of disparate schemes developed by various computer scientists, for the computational representation of visual information, and it is perhaps not altogether clear what these have in common as alternatives to a pictorial conception of imagery. The vocabulary and syntax of mentalese if it exists remain unknown, but they are likely to be very different from those of English or any other natural actually spoken language.

Nevertheless, Fodor holds that any cognitive theory capable of accounting for the full range of human mental capacities is bound to make appeal to some such inner language. This means, of course, that Pylyshyn's positive view of imagery — description theory — is viable only if the controversial language of thought hypothesis is true. However, many of Pylyshyn's objections to pictorial theories of imagery might still stand even if this were not the case. Fodor did not , however, embrace Pylyshyn's objections to pictorial mental imagery. Although he holds that pictorial representations are not sufficient to support cognition on their own, and are probably dependent on associated mentalese representations for playing any cognitive roles that they do play, he nevertheless argues against some philosophical objections to mental pictures, [ 33 ] and thinks that the empirical evidence from psychologists such as Paivio and Shepard suggests that images do in fact play a real role in our cognitive processes Fodor, pp.

It is sometimes objected that a description theory, like Pylyshyn's, is incompatible with the phenomenology of imagery e. After all, having a mental image of a cat does not seem anything like reciting a description of a cat to oneself. However, this seems to be based on having drawn too close an analogy between the mentalese descriptions intended by the theory and descriptions in English or other natural languages. In the first place, although we can be conscious of English sentences as such, we are pretty much ex hypothesis never conscious of our mentalese representations as such, but only at most of what they represent.

Thus there is no reason to expect that entertaining a mentalese description would subjectively seem anything at all like reciting, or reading, or otherwise thinking of a description in English. Thus his theory readily accounts for the phenomenological similarity between imagery and perceptual experience. If, as seems likely, the perceptual descriptions are typically more detailed than those of imagery, this might also account for any phenomenological differences between imagery and perception.

This introspectively based argument against description theory, weak though it is, is often prelude to the even stronger claim that the phenomenology of imagery directly supports the view that mental images are inner pictures. After all, it is said, in contrast to reciting a description to oneself, having a mental image of say a cat does seem very much like seeing a picture of a cat.

Although some people seem to find this argument tempting e. There is little or nothing to the alleged similarity between the experience of having a mental image of a cat and that of seeing a picture of a cat, apart from the fact that both these experiences in some ways resemble the experience of actually seeing a cat, and both differ from it in that no cat need actually be present.

Pictures and mental images also differ in important ways. It is generally possible, for instance, to turn over a picture and look at its blank backside, to examine its surface for marks such as scratches or dirt that do not have a depictive role, or to look at its flat surface from an oblique angle so that what it depicts appears distorted.

You cannot do such things with a mental image. It is true that pictures paintings, drawings, photographs, videos, etc. Indeed, pictures and sculptures may be our only familiar example of this, apart from mental imagery itself. However, it does not follow that mental images must therefore be a species of picture. The easy analogy may be a false one. In fact, neither Paivio nor Shepard, who were undoubtedly the best known imagery researchers at the time Pylyshyn published his initial critique, were committed to the straightforward picture theory of imagery that he seemed to be criticizing.

Cooper, Neisser developed the notion of imagery as perceptual readiness or anticipation into a theory of imagery explicitly opposed to both the picture and description theories Neisser, , a, b; — see section 4. Finke's experimental work on visual illusions and aftereffects induced by imagery Finke, , ch.

Gibson , However, Stephen Kosslyn soon intervened in the debate, proposing a theory of visual imagery that was both explicitly computational and overtly pictorialist or, as he prefers, quasi-pictorial , based on an analogy with computer graphics programs which were a fairly new thing back then Kosslyn, As the leading figures on each side were now both firmly wedded to the theoretical framework of computational functionalism, [ 39 ] the debate's scope was, in practice, greatly narrowed by this development, even as its intensity and contentiousness and notoriety grew.

It developed not into an open ended inquiry into the nature and causes of imagery, but a manichean struggle between the computational pictorialism championed by Kosslyn and his supporters, and the computational description theory still most ably and enthusiastically represented by Pylyshyn. It ought to be noted, however, that this discussion largely depends on the speculative ascription of straw-man accounts of these, at the time newly discovered, effects to Pylyshyn, or to description theorists in general. Pictorial theories had shown themselves to be scientifically fruitful in a way that description theories had not.

On the face of things, description theory predicts that imagery should depend upon the mechanisms and brain structures that subserve conceptual, non-imaginal thought, and not those that subserve perception. Incidentally, although it was once widely believed that visual imagery in humans was primarily a function of the right hemisphere of the brain e. He calls the theory quasi -pictorial, to avoid the implication that he thinks images are pictures in too literal and implausible a sense. Quasi-pictures are not the sort of thing that can be hung on a wall Kosslyn, b , and you do not need actual eyes inside the head looking at them in order to experience them.

Nevertheless, they remain like pictures in many important respects. It remains controversial whether there can be a coherent notion of a quasi-picture that both retains the explanatorily useful properties of true pictures such as their inherent spatiality, and their capacity to cause visual experiences as of what they represent and, at the same time, lacks those properties that make it impossible for true pictures to be mental, or even neural, representations such as needing to be illuminated and before our eyes in order to be experienced.

It is clearly Pylyshyn's opinion that there is no such notion, and that much of the superficial plausibility of quasi-pictorial theory depends upon an equivocation between the relatively well understood concept of a picture in the everyday sense, and the essentially non-pictorial notion of an array data structure Pylyshyn, , a, b. The literal picture in the head theory appeals to our folk-theoretical intuitions, makes interesting predictions, and has the resources to be genuinely explanatory, but it is demonstrably false. On the other hand, the data-structure theory to which quasi-pictorialists retreat when literal pictorialism is challenged is really just a version of Pylyshyn's own description theory, and, properly understood, has none of the special intuitive, explanatory, or predictive advantages that picture theorists claim for their views.

Any apparent similarity between pictures and two-dimensional array data structures is, according to Pylyshyn, no more than an artifact of the way we customarily present such arrays on paper or screen for the benefit of human eyes. It has nothing to do with their actual mathematical properties, or with how they might function in cognition.

Despite Pylyshyn's criticisms, however, many philosophers have clearly been impressed by Kosslyn's work. Some have directly defended the quasi-pictorial theory of imagery, attempting to clarify the notion of a quasi-picture, and to show that it has real content von Eckardt, , , ; Tye, , ; Cohen, Others are more circumspect, or less committed to the specifics of Kosslyn's theory, but are now persuaded to countenance the possibility of picture-like mental representations of some sort e.

Sober, ; Block, a, b, a, b; Bower, ; Sterelny, ; Rollins, , ; Mortensen, ; Dennett, ; Brann, Yet others, however, for reasons discussed in the previous section and the following supplement , remain entirely unpersuaded e. Reading most of the recent philosophical literature on imagery and, it must be admitted, most of the broader cognitive science literature, especially textbooks one might easily form the impression that quasi-pictures and "propositional" descriptions are the only possible theoretical models for imagery, or, at least, the only ones ever seriously proposed or considered. This is not the case, however.

Even in the 70s, however, a number of alternative, non-computational accounts of imagery were being put forward. On the one hand, Taylor and Skinner looked for ways to assimilate imagery into Behaviorism. Enactive theories of imagery may be seen as modern successors to the motor theories of the early twentieth century see Supplement: The American Response: Behaviorist Iconophobia and Motor Theories of Imagery. The perceiving organism is not merely registering but exploring and asking questions of its environment Ellis, , actively and intentionally though not necessarily with conscious volition seeking out the answers in the sensory stimuli that surround it.

We have imagery of, say, a cat, when we go through some of the motions of looking at something and determining that it is a cat, even though there is no cat and perhaps nothing relevant at all there to be seen. Visually imagining a cat is seeing nothing-in-particular as a cat Thomas, b, , ; cf.

Ishiguro, However, with those exceptions, in the s and 80s the enactive approach to imagery attracted very little attention. It was not just that these non-computational theories seemed irrelevant to psychologists and philosophers whose focus was on integrating imagery into the prevalent symbolic, GOFAI Haugeland, computational model of the mind. More specifically, the enactive theories do not fit comfortably, if at all, into the framework of computational information processing theory that shaped most scientists' thinking about perception and perceptual experience.

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Information processing theories come in many varieties, but they all, broadly speaking, depict the sense organs as passive transducers of stimulus energies light, sound, etc. They differ merely in that Kosslyn holds that the representations comprising imagery are formed at an early stage of visual processing, whereas Pylyshyn holds that they are formed at a late stage.

This difference, however, gave rise to the impassioned analog-propositional debate, whose sound and fury only served to further distract attention from theoretical alternatives that did not fit the information processing paradigm. Since the mid s its hegemony has been repeatedly challenged, first by connectionism e. The robotic system Murphy , designed by Mel , has some interesting features in that it combines such a connectionist model of visual imagery with a model of trial-and-error learning of motor control, wherein information in the putative image is used to control the reaching behavior of a robotic arm although it is not obvious that imagery, as distinct from visual perception, plays any such role in human reaching.

Nevertheless, Mel and Grush continue to conceive of the image itself as being a two dimensional array of elements, just as the quasi-pictorial theory of Kosslyn does, and, indeed, in support of their models both Mel and Grush follow Kosslyn in appealing to evidence about the spatial properties of imagery and about the involvement of visual areas of the brain in imagery. Thus, despite the fact that Mel and Grush situate their accounts of imagery in the context of motor control rather than of visual cognition, they remain quasi-pictorial accounts, and are, in most respects, considerably less developed than though perhaps consistent with the version of quasi-pictorial theory developed by Kosslyn.

As such, they share most of the virtues of Kosslyn's version, and are subject to the same objections see supplement: The Quasi-Pictorial Theory of Imagery, and its Problems. Dynamical systems theory has also had relatively little to say about imagery, although Freeman has sketched an account of olfactory imagery in terms of neural dynamics.

He explicitly distances himself from both sides of the analog-propositional debate, and makes appeal instead to the concept of search image as used in the science of Behavioral Ecology. A search image is to a first approximation a specific, learned recognitional capacity, or a form of selective attention, that leads a predator species to recognize and preferentially prey upon members of the more abundant prey species in its environment, whilst largely failing to notice less abundant types of potential prey Tinbergen, ; Atema et al.

However, it is less than clear that Freeman is justified in conflating this concept of search image with that of mental image, as used in folk psychology and cognitive science. It is mainly the rise of situated and embodied approaches to cognition that has challenged the information processing approach to perception, and enabled the re-emergence and further development of enactive imagery theory.

During the s, robotics researchers interested in creating robots to operate in real wold environments were finding that getting a machine to process information from sensory transducers into an internal representation of its surroundings that would provide a suitable basis for action planning was a very difficult computational problem. Indeed, some became convinced that, even if it could be done in principle, in practice the process would be unacceptably slow, unreliable, and computationally expensive by the time the robot knew what was going on, things would have changed.

Instead of attempting to build up detailed internal representations of their environment, robots began to be designed to deploy their sensors purposively, to actively seek out just the specific information needed at that particular moment for making an impending behavioral decision e. At around the same time, a number of neuroscientists, perceptual psychologists, and philosophers began, for diverse reasons, to converge on a similar view of human vision Ramachandran, ; O'Regan, ; Churchland et al.

We do not have our sense of the immediate perceptual presence of the world because we have a representation of it in our heads, but rather because these routines operate for the most part so quickly and effortlessly that virtually as soon as we want to know some perceptually available fact, we are able to discover it. Thomas b argues that enactive theory can explain experimental cognitive psychology's findings about imagery see sections 4. It has also been argued that enactive theory can provide a more satisfactory explanation of the neurological evidence about imagery i.

Other relevant evidence comes from studies of eye movements during imagery. Saccades are quick, mostly unconscious, flicks of the eyes, which are now known to play an important role not only in vision, but in visual imagery as well. It has also become apparent that saccades and perhaps other types of eye movement too play a significant role in visual mental imagery. Furthermore, imagery is disrupted to a greater or lesser degree if someone who is holding an image in their mind either restrains themselves to the limited degree that this is possible from making eye movements, or else deliberately moves their eyes in an image-irrelevant way, thus disrupting the spontaneous saccadic pattern Antrobus et al.

This issue has been much researched lately, not so much because of its significance for our understanding of imagery, but because of its possible relevance to the understanding of the psychotherapeutic technique known as EMDR Eye Movement Desensitization and Reprocessing , which is widely used in the treatment of Post-Traumatic Stress Disorder PTSD , and which may perhaps owe its effectiveness largely to the fact that deliberate eye movements tend to disrupt any concurrent imagery.

Although the mechanisms and real therapeutic effectiveness of EMDR remain controversial for negative opinions, see: Lohr et al. Although all subjects formed images of the same figures, some originally formed them on the basis of verbal descriptions, whereas others were shown separate segments of the entire structure to be visualized, and asked to assemble them mentally into the complete figure.

The PET scan was not taken at the time the images were originally formed in one or other of these ways, but when they were later recalled. According to the experimenters, enactive theory holds that when someone recalls a mental image they re-enact what they did at the time of its original formation, and since the two subject groups originally formed their images in very different ways, the theory predicts that the two groups should display radically different patterns of brain activation at the time of recall.

In fact, however, no marked differences were seen. This is claimed to constitute a refutation of the enactive theory. It rests, however, on a demonstrable misunderstanding of the theory. No version of enactive imagery theory holds either explicitly or implicitly what these experimenters claim it holds: that recall of mental imagery is constituted by re-enactment of whatever was the original act of image formation.

What enactive theory in fact holds is that imagery recalled or otherwise is constituted by partial enactment of the perceptual acts that would be carried out if one were actually perceiving whatever is being imagined Johansson et al. It is true that in the most straightforward and paradigmatic case of mental image formation — the direct recall of an earlier perceptual experience of something — enactment of what one would be doing if actually perceiving that thing is equivalent to re -enactment of what one did during the original perceptual episode.

However, this equivalence clearly breaks down in most other circumstances, including those of the experiment in question. Since both groups of subjects in the experiment under discussion were supposed to be recalling an image of the same geometrical pattern when their brains were scanned, enactive theory actually predicts that the neural activity due to the recalled image should be much the same in each group, just as was found. Quite apart from empirical evidence, certain distinctively philosophical advantages have been claimed for enactive theory.

It has been suggested that it is better able than its rivals to explain imaginal consciousness Ellis, ; Thomas, b, , ; Bartolomeo, , and Thomas , a, b, argues that enactive theory can provide the basis for an understanding of the concept of imagination , whereas quasi-pictorial theory and description theory cannot see also: Blain, ; Agnati et al. Traditionally, both philosophers and the folk have thought of the imagination as a mental faculty responsible both for mental imagery, and for the most admired forms of artistic and other creativity.

It has also been suggested Newton, , ; Thomas, b, , ; see also Heil, ch. However, if mental images are as just about everybody believes a species of mental representation, these latter claims are at odds with the idea that mental representations are token identical to brain states. It seems likely that mental imagery has been discussed for as long as humans have been trying to understand their own cognitive processes.

It receives attention in the oldest extended writings about cognition that have come down to us — the works of Plato and Aristotle — and there is reason to believe it was discussed by yet earlier Greek thinkers. Plato's and particularly Aristotle's writings have undoubtedly had an enormous and continuing influence on how cognition in general and imagery in particular are conceptualized within both the Western and the Muslim cultural traditions.

However, there is reason to think that the phenomenon of imagery, if not this tradition of theorizing about it, is not culture bound. Thus, of necessity, what follows will focus on the Western philosophical and scientific tradition. In any case, the seeds of the controversies about imagery that erupted in the 20 th century were sown not in Africa or the Orient, but in Greece. The following supplements discuss Greek conceptions of imagery prior to the work of Aristotle:.

Supplement: Ancient Imagery Mnemonics. Supplement: Plato and his Predecessors. Where Plato regarded images as irremediably deceptive, Aristotle, although he certainly recognized their potential for leading us astray De Anima a-b , saw them as playing an essential and central role in human cognition, one closely akin to that played by the more generic notion of mental representation in contemporary cognitive science.

Indeed, he developed what amounts to the first comprehensive cognitive theory, a theory that has been enormously influential over the subsequent ages, and continues mostly indirectly to shape much scientific and philosophical thought about the mind even today. He was clearly aware of, and very possibly influenced by, the mnemonic imagery techniques in use in Greece see supplement , to which he alludes in at least four passages in his extant writings Topica b28, De Anima b18, De Memoria a12—16, De Insomniis b20— Some modern scholars, it should be noted, have questioned the translation of " phantasma " as "image," in part because Aristotle does not always seem to think of phantasmata as inner pictures, and also because he seems to think of them as playing a role in perception itself Nussbaum, ; Schofield, ; Birondo, As Hume distinguished impressions from ideas , contemporary colloquial English distinguishes between percepts and the mental images that we experience when we fantasize, daydream, or recall some experience from memory.

Aristotle's concept of phantasma seems to collapse this distinction. It has thus been suggested that "phantasma" would be better translated as "appearance" Lycos, or "presentation" Beare, rather than as "image". However, contemporary scientific theories of imagery see sections 4.

In any case, it is abundantly clear that, in many even if not all cases, Aristotle uses " phantasma " to refer to what we now call a mental image. Phantasmata have several functions paralleling those ascribed to imagery by modern folk psychology and some scientific psychology. In particular, they are central to Aristotle's theory of memory De Memoria et Reminiscentia ; see Sorabji, and to his theory of thought.

Not only does remembering essentially involve the recall of imagery of past experiences, but, he tells us, "It is impossible to think without an image [ phantasma ]," De Memoria a 1; cf. Phantasmata also play a key role in his account of desire and motivation e. De Anima a — see Nussbaum, : When some desirable object is not actually present to our senses, exerting its pull on us directly, our motivation to strive to obtain it is driven by our awareness of its memory or fantasy image. This idea is still found in modern, scientific theories of desire McMahon ; Kavanagh et al. Aristotle also apparently held that linguistic meaning derives from imagery, spoken words being but the symbols of the inner images De Interpretatione 16a 5—9; De Anima b 29—32; see Modrak, Today, few theorists of language take this notion seriously but see Paivio, , ; Prinz, , but it was almost universally accepted until relatively recent times Wollock, ; and see section 3.

Aristotle has been accredited with the very invention of the concept of imagination Schofield, , and certainly it seems fair to say that the roots of most subsequent discussions of the concept can be traced back to his work even though, for him, it did not have the strong association with creativity and aesthetic insight that it has since acquired, mostly through the influence of the Romantic movement Watson, ; White, ; Thomas, a. Unfortunately, however, Aristotle's remarks about phantasia , suggestive and influential though they are, are scattered widely amongst the surviving texts, and the only extended discussion of the concept in De Anima III.

After over two millennia of discussion, scholars still do not agree about crucial aspects of Aristotle's conception of phantasia , and thus about his view of the fundamental nature of imagery. It can hardly be denied that the concept of the idea was central to much of modern philosophy. Ideas were mental representations, and very frequently, though not necessarily always, they were explicitly or implicitly conceived of as mental images.

Even if some authors did not themselves take ideas to be images, it is likely that many of their readers would have taken them to be doing so.

Classics in the History of Psychology -- Galton ()

Thus, claims about the nature of ideas, and the cognitive and epistemological roles they could or could not play, were often conditioned by whether or not a philosopher did conceive of ideas as images, and by what imagery was taken to be. We are told that we can attain clear and distinct ideas of such things as God and the human mind Meditation 4 , Neither of these are things of which we have perceptual, let alone quasi-perceptual, experience.

But Descartes insists that even our ideas of perceptible things are, inasmuch as they are clear and distinct, not perceptual or imaginative. His perceptual and imaginative grasp of the nature of a piece of wax, he tells us, can never match the clarity and distinctness of the idea of the wax that can potentially be attained by purely mental scrutiny Meditation 2 , However, we also find in Descartes' work another conception of idea as something that is quasi-perceptual and, indeed, pictorial and is formed in the imagination.

These ideas may not be capable of providing the sure epistemological foundation that Descartes thinks the clear and distinct ideas of the intellect can give us, but they are real nonetheless, and probably play a larger role in ordinary, non-philosophic thinking. Although they are alluded to in many of Descartes works, these imagistic ideas are explained most fully in the Treatise of Man , where he propounds his speculative physiological theory of visual perception in some detail.

Figure 2. The tracing of the image on its surface causes the gland to move in a subtle and complex fashion that in some unexplained way causes a conscious visual experience of the arrow in the soul Descartes — see particularly pp. At the same time that the flow of animal spirits is causing visual experiences by moving the pineal, elsewhere in the brain it is causing visual memories to be laid down by its action upon the nerve fibres themselves.

These changes to hydraulic structure of the brain allow for mental images of memory and imagination to arise by the recreation of formerly experienced flow patterns of spirits at the pineal surface. However, this was clearly not Descartes' own practice. The thought here seems to be that all ideas as such are in our minds, although some of them are caused or occasioned by the presence of an image on the pineal surface.

It is beyond the scope of this entry to determine what was truly Descartes' considered view. What is clear, however, is that Descartes' readers would have readily been able to find a concept of the idea as a picture-like image in his writings. It is notable, however, that this comparison is made in the course of an argument to the effect that the representations in the brain that cause our perceptual and imaginative experiences need not actually resemble their objects: the resemblance between an engraving and what it depicts is, after all, very partial and imperfect.

What matters, for Descartes, is that the conscious soul is appropriately affected by the movements that the process of image formation causes in the pineal gland. Thus it is the functional role of the image, not its actual physical nature, that is important. As a materialist, Hobbes, unlike Descartes, does not distinguish between images formed in the brain and ideas in the mind. In fact, although Hobbes sometimes uses the word 'idea' as a synonym for 'image,' it occurs rather infrequently in his writings, and he prefers to use 'image' or 'imagination' or other synonyms such as 'phantasm' or 'appearance.

Images, however, are undoubtedly central to his cognitive theory. However, it is not necessarily the case that Hobbes thought of his images, even those of visual appearances, as being picture-like. Rather, it is that of a movement gradually running out of impetus, a pendulum swing gradually decreasing in amplitude, or a gas under pressure gradually leaking away. Furthermore, Hobbes, unlike Descartes, did not think of memory as being the result of structural changes in the brain, but rather as arising from the persistence, the very slow dying away, of the internal motions that were originally set going by sense experience Leviathan I.

Although they are undoubtedly quasi-perceptual experiences presumably, in the absence of an immaterial soul, we are to suppose that they are experienced merely in virtue of their occurring within the brain they may not be mental pictures in any very robust sense. Unlike his predecessors, Locke did not concern himself with the nature or underlying mechanisms of mental imagery.

Henceforth, at least until the rise of cognitive science in the late 20th century, that would be seen as the concern of scientists rather than philosophers [ 13 ] and as it turned out, the scientists did not have much to say about the matter either, until, once again, the era of cognitive science. Furthermore, Locke's Essay Concerning Human Understanding uses the words 'image' and 'imagination' only rarely White, ; Ayers, p.

It is thus hardly surprising that, according to Lowe p. This orthodoxy is defended by Ayers , and White amongst others, but other recent Locke scholars, notably Yolton , , , , , Chappell , and, more tentatively, Lowe , challenge it, arguing that the explicit comparisons of ideas with pictures are all limited merely to bringing out some or other specific aspect of the nature of ideas, and should not be read as identifying them with pictures. According to Yolton, there is no evidence that Locke thought of ideas as entities of any sort Yolton p. Enactive theories of imagery see section 4.

He certainly held that they arise from perception, [ 15 ] and that we are conscious of them when we employ them in our thinking Essay II. Whatever Locke's true intentions may have been, many of his leading successors and critics, such as Berkeley and Reid, seem to have understood him as believing that ideas are inner representational entities, and, when visual, are like inner pictures.

Few seem to doubt that Berkeley thought of ideas as being images but see Pitcher, ; Kasem, Indeed, his famous and influential attack in The Principles of Human Knowledge on the possibility of abstract or general ideas clearly derives most of its persuasiveness from the assumption that ideas are like pictures:. In effect, Berkeley is arguing that we can form ideas of things that we have never actually seen just inasmuch as we can form new mental pictures by the sort of cutting and pasting operations we could perform with pictures on paper — sticking the picture of a man's head onto a picture of the body of a horse, for example — but that, just as there is no way of drawing or creating a picture that inherently depicts the general man or the general triangle, we can form no such general ideas in our minds.

If they are not images at all, it makes little sense and if mental images are not much like pictures, it is probably invalid. As with Locke, Yolton argues that Hume did not understand the ideas of his cognitive theory to be mental images. However, there is a great deal in Hume's writings much more than in Locke's to suggest otherwise.

It is conceivable that 'image' might mean nothing more than 'copy' here, but many other passages in both the Treatise and the Enquiry Concerning Human Understanding suggest that Hume intended it in a much stronger sense. The passages just cited and others like them perhaps imply no more than that Hume thought of ideas as quasi-perceptual experiences a conclusion that Yolton might be able to accept , but the fact that Hume approvingly repeats Berkeley's argument against general ideas Treatise I. This is also suggested by his choice of the word 'impression' to designate the percepts of which ideas are the images or copies.

Clearly the word alludes to the wax impression model of perception and memory that we find in Plato and Aristotle, and although Hume, no doubt, does not intend it to be understood too literally, the fact that he thinks it an appropriate and innocuous metaphor remains telling. Reid is not saying that we do not have quasi-perceptual experiences, but he wants to deny that these are caused by representational mental entities that we experience in lieu of some actually present physical object or scene.

However, images still have a significant role to play in his account of how our concepts connect to empirical reality. The imagination einbildungskraft must synthesize the inchoate deliverances of the senses, the sensory manifold, into a coherent, meaningful image, a true representation that the understanding can grasp and bring under some concept.

Unfortunately, Kant was unable to give a satisfactory account of how the imagination, even in concert with the understanding, can achieve this. Unfortunately, however,. Thus Kant, in attempting to grapple with problems about the nature of mental representation that the Empiricists had failed to solve, left the process of image formation, and the nature of the image itself, deeply mysterious. When psychology first began to emerge as an experimental science, in the philosophy departments of the German universities in the late 19th century, and soon after in the United States, the central role of imagery in mental life was not in question.

For these pioneering experimentalists, such as Wilhelm Wundt in Germany and William James in America, mental images often, following the established usage of the Empiricist philosophical tradition, referred to as ideas held just the same central place in the explanation of cognition that they had held for philosophical psychologists of earlier times. Edward B. Titchener, a student of Wundt who established himself as a leading figure in American psychology, was particularly interested in imagery, and an experiment performed by one of his students, C.

Perky, has become particularly well known. It is often assumed that it shows that there is no qualitative experiential difference between mental images and percepts, but further experimental investigations have raised some doubts about this conclusion see Supplement: The Perky Experiment. However, developments within psychology at the beginning of the 20th century began to cast doubt on this long established consensus.

Their results were challenged on several grounds by Wundt, Titchener and others, and were certainly never definitively established. Nevertheless, the bitter dispute that ensued, the so called imageless thought controversy, had a profound effect on the development of scientific psychology and, very arguably, philosophy too. Most psychologists became, in effect, profoundly disillusioned with the whole notion of mental imagery, and either avoided seriously considering the topic, treated it dismissively, or, in some extreme cases, denied the existence of the phenomenon outright.

These attitudes noticeably influenced other disciplines, including philosophy. Although the psychological study of imagery revived with the rise of cognitivism in the s and 70s, when new experimental techniques were developed that enabled a truly experimental study of the phenomenon, current views about, and attitudes towards, mental imagery cannot be properly understood without an awareness of this history, versions of which, of varying degrees of accuracy, have passed into the folklore of psychology.


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  • The following supplements discuss ideas and research about imagery in early late 19th and early 20th century scientific psychology:. Supplement: Edward B. Titchener: The Complete Iconophile. He and his students there developed a direct challenge to the prevalent imagery theory of thought. In , two of these students, Mayer and Orth, performed a word association experiment in which subjects were asked to report everything that had passed through their mind between hearing the stimulus word and giving the response.

    Note that it was normal practice, in this era of psychology, for experimental subjects, or observers as they were more often called, to be drawn from among fellow researchers within the same laboratory, often including the supervising professor. Present day psychologists would, with good reason, suspect such subjects of being liable to produce results strongly biased by theoretical preconceptions Orne, ; Intons-Peterson, 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.

    In however, it was thought that experienced and knowledgeable observers were more likely to produce consistent and meaningful results than the psychologically untrained. In the case of the Meyer and Orth experiment, two amongst the four subjects were Meyer and Orth themselves. Nevertheless, they professed to be surprised by some of their findings. In particular:. Unsurprisingly, Wundt, and others, refused to accept these new methods and conclusions, and a heated debate, the so called imageless thought controversy, ensued.

    Though Wundt was surely skeptical of the existence of imageless thoughts, his primary criticisms were methodological. He was very much concerned with the fact that the experiments were necessarily constructed so that the introspective reports were given after the completion of the experimental task word association, sentence interpretation, or whatever. Such experiments, Wundt argued, were open invitations to suggestion, and, indeed, were. Titchener see supplement also strongly objected to the alleged demonstrations of imageless thought, but for different reasons.

    Titchener suggested that the purported bewusstseinslagen etc. Instead, they found the fleeting imagery or the subtle bodily sensations that Professor Titchener's theory predicted Titchener, ; Humphrey, This work of Titchener's like other responses to the imageless thought controversy from America, Britain, and elsewhere had relatively little impact in Germany, which, with some justification at that time, still regarded itself as very much preeminent in psychological science.

    Nevertheless, on both sides of the Atlantic the controversy was recognized as touching on deep foundational issues in the science of mind. Although largely forgotten today, it seems to have had a lasting impact on the development not only of psychology, but philosophy as well. Many psychologists and philosophers of this era came, partly for this reason, to feel that thought should be understood in terms of language per se , and that it was a serious mistake ever to have believed that the representational power of language derives from some more fundamental form of representation, such as mental imagery.

    But the imageless thought controversy was never satisfactorily resolved, at least in the terms in which it was originally posed. Indeed, philosophers are still arguing over the issues involved e. The irresolvable dispute contributed significantly to a growing sense of intellectual crisis within psychology, leading to a deep loss of confidence persisting to the present — see Schwitzgebel a,b, in the scientific value of introspection.

    It also led to a precipitous decline in scientific interest in imagery, especially in the United States after the Behaviorist movement took hold. On the one hand its importance in the cognitive economy or even its very existence was now subject to doubt; on the other hand it had come to seem that it was very difficult, if not impossible, to study it experimentally and objectively. By the early 20th century, particularly in the United States, where it most flourished, psychology had progressively established a disciplinary identity distinct from the parent discipline of philosophy.

    However, interest in and attitudes towards imagery amongst philosophers followed a very similar trajectory to that seen in psychology. Images, he pointed out, are subjective and idiosyncratic, whereas word meanings are objective and universal. Today, it is largely thanks to Wittgenstein's efforts that,. Many other remarks and arguments scattered through Wittgenstein's other posthumously published writings, particularly in Zettel , the Remarks on the Philosophy of Psychology a, b , and the Last Writings on the Philosophy of Psychology , demonstrate that he was fascinated by imagery, but deeply skeptical not only about the large cognitive role traditionally assigned to it, but also about the traditional understanding of the image as a sort of inner picture see, e.

    No-one could seriously doubt that Wittgenstein himself recognized the experiential reality and philosophical importance of imagery: he expends so much effort wrestling with the concept. Instead, Wittgenstein regarded language itself as the preeminent vehicle of thought, and he held that the meanings of linguistic expressions arise from the various uses to which they are put. He thus saw no need and no room for language to be semantically grounded in any other form of representation.

    In support of this position, he strove to show that imagery the only real candidate for the job could not possibly be the semantic ground of language, and he is very widely believed to have succeeded. The two themes of the cognitive unimportance of imagery and its non-pictorial nature were taken up, and argued more fully, by numerous post-Wittgensteinian philosophers in the latter half of the twentieth century. Although there may be some tension between the themes most arguments against the imagery theory of thought and meaning seem to turn upon mental images being, in some sense, picture-like in practice they have rarely, if ever, come into conflict; rather, both have played their part in setting the iconophobic tone of the era.

    Philosophers such as Harrison —3 , Goodman , and Fodor have reinforced, restated and extended Wittgenstein's arguments for the irrelevance of imagery to semantics, and have made a powerful and influential case. One point that is often made is that there seems to be no natural way of representing certain linguistically expressible concepts in an image. Logical relations are often mentioned in this context. It is hard to see, for example, how it might be possible to form a mental image of not is any image in which John does not appear an image of John is not here?

    The image theory of linguistic meaning might seem to be on its strongest ground when it is applied to nouns or, at least, concrete nouns. On the face of things, it is plausible to think that one understands the meaning of the word 'dog' if and only if as the word is able to arouse an image of a dog in one's mind. Berkeley's argument against general ideas had long brought this simple picture into question, however see section 2. Can my mental picture of a dog represent any dog, or dogs in general, or is it, at best, just a representation of Rover?

    Twentieth century philosophers, however, would soon point to an even deeper problem. They assumed, probably often correctly, that the traditional image theory of meaning was based upon the assumption that images themselves get their meaning through resembling their objects: an image of a dog represents a dog because it resembles or looks like a dog, in the same way that a painting of Queen Elizabeth represents Queen Elizabeth because it looks like her. This resemblance theory of representation is not always explicitly stated by image theorists of thought and language perhaps it is thought to be too obvious to be worth saying, or perhaps not all of them are really committed to it , but Russell , , for one, explicitly takes the view that words represent because they are associated with mental images, and that the images themselves represent because they resemble their objects.

    This resemblance theory became the main focus of attack. Consider a photograph of Leo the lion. It would certainly be reasonable to say both that it resembles and that it represents him. But now suppose we have two such photographs. Each photo resembles the other more than either resemble Leo both photos are small, rectangular pieces of card, with a white border around a gray or vari-colored rectangle, and neither is carnivorous or furry , yet we would normally want to say that they each represent Leo, and not that they represent each other.

    Of course, a photograph of Leo does resemble him, when the right aspects of resemblance are considered, but in this regard Leo equally resembles the photograph. We are unlikely, however, to want to say that he represents the photo. Resemblance is a symmetrical relationship, and representation is not. None of this necessarily means that resemblance never plays any role in representation, but in order for it to do so, the relevant aspects of resemblance have to be recognized, and the resembling object has to be used or, at least, taken as a representation.

    But surely, before a cognitive system can recognize or use the relevant aspects of resemblance between a photograph or an inner quasi-picture and an object or a percept , it must already be able to represent the picture and its object, and their various features, to itself. The mind's power to recognize resemblance seemingly depends on its power to represent things, rather than vice-versa. On grounds such as this, Goodman argued that even physical pictures — paintings drawings, photographs, etc.

    Clearly the argument applies to mental pictures quite as much as to physical ones. Goodman, A mental image of John, who is a tall fat man, might mean John , it might mean fat man or John is a fat man , or tall man , or just man , human being , or even physical object. On the other hand it might mean John in just the particular pose and situation in which he is imagined. After all, it resembles all those things and indefinitely many more. What an image means, according to Fodor, what it is an image of , will necessarily remain radically indeterminate unless it is pinned down by an associated linguistic description.

    On either view, though, the traditional semantic dependency is inverted. Instead of the meaningfulness of language being grounded in imagery, the meaningfulness of imagery seems to need grounding in some sort of language. Arguments against the pictorial nature of imagery, which are scarcely more than hinted at in Wittgenstein's published works, were developed much more explicitly by Ryle Other philosophers influenced by both Wittgenstein and Ryle soon carried forward this critique of the inner picture: Shorter and Dennett in some respects anticipating the work of Pylyshyn — see section 4.

    Although expressed in very different terms, Ishiguro's position on imagery is not altogether unlike the view developed earlier in the century by Sartre See Ryle for an interesting comparison of his own views about the mental, including mental imagery, to views in the phenomenological tradition, to which Sartre belonged. Under the influence of Husserl rather than Wittgenstein, Sartre also stressed the intentionality of imagery and denied that mental images conceived as entities exist:. It is important to be clear that just because Sartre and Ryle, Shorter, Ishiguro, and others hold that mental images are not inner pictures, nor even, indeed, any sort of entity, they are not thereby denying that people have quasi-perceptual experiences, or even that these may sometimes be very vivid.

    Unfortunately, perhaps because the notion that such experiences are caused by inner pictures is so entrenched in our folk psychology, this point does not always seem to have been clear to critics of such views, and it has even been occasionally suggested that they could not possibly be held by anyone personally familiar with the experience of imagery. By contrast, in his Mental Images — A Defence , Hannay vigorously championed the reality of inner pictures see also Hannay, , and for a counterargument see Candlish, But, despite the fact that he had no thought of reinstating imagery to its traditional importance in cognitive and semantic theory, Hannay clearly saw himself in as a lonely dissenter, a voice crying in the wilderness against philosophy's virtually monolithic iconophobic consensus.

    In the subsequent decades that consensus has been fractured, but by no means shattered, by developments in cognitive psychology and cognitive science discussed below. In particular, in the wake of Kosslyn's , seminal work on the cognitive psychology of imagery, a growing number of philosophers are now ready to defend the reality of mental pictures, and show no sign whatsoever of feeling embattled e.

    Many other philosophers, even if not entirely convinced about pictures, now take a serious interest in the cognitive science of imagery. Nonetheless, the post-Wittgensteinian consensus that imagery cannot be as important as it once seemed to be, that it cannot be the ground of linguistic meaning or the prime vehicle of thought, remains strong. Despite all that has happened in cognitive science, imagery has by no means regained its former prominence in philosophy.

    A revival of interest in imagery was an important component of the so called cognitive revolution in psychology during the s and early s, a period when the Behaviorist intellectual hegemony over the field was broken and the concept of mental representation was established as central and vital to psychological theorizing Baars, ; Gardner, ; but see also Leahey, Although the emergence of computational models of mental processes probably played the leading role in the rise of cognitive psychology and cognitive science, the new interest in imagery was independently motivated, and contributed significantly to the growing feeling, amongst psychologists, that both the ontology and methodology of Behaviorism were excessively restrictive, and that inner mental processes and representations could, after all, be useful, or even indispensible, scientific concepts.

    Quite apart from the broader talk of revolution in psychology in this era e. Holt indicates a number of developments that began to lead some psychologists, in the s, to begin to pay significant attention to imagery again. These include research on hallucinogenic drugs, developments in electroencephalography, the discovery of REM sleep and its correlation with dreaming, and Penfield's finding that direct electrical stimulation of certain brain areas can give rise to vivid memory or pseudo-memory imagery.

    More significant, however, according to Holt was a line of psychological research that was originally inspired by practical, rather than theoretical, concerns: by the perceptual problems experienced by people such as radar operators, long-distance truck drivers, and jet pilots, whose work requires them to remain perceptually alert whilst watching monotonous, impoverished, and barely changing visual stimuli over extended periods of time.

    Despite the introspective nature of the evidence, the practical implications of these findings for such things as road and air safety made them hard to dismiss. Beginning in the s, and perhaps stimulated by some of the research mentioned by Holt, there was also a growing interest in the application of imagery based techniques in psychotherapy and psychosomatic medicine see, e. A journal dedicated to the subject, the Journal of Imagery Research in Sport and Physical Activity commenced online publication in Great claims are also made, by some, for the healing powers of guided imagery , whereby clients or patients are encouraged to visualize particular scenes or scenarios thought to have therapeutic value e.

    Guided imagery techniques have been claimed to be effective for purposes ranging from chronic pain relief and the preparation of patients for surgery Fontaine, ; Tusek et al. It is sometimes claimed or implied that these sorts of techniques are based upon ancient oriental, and particularly Indian, spiritual practices e. The journal publishes articles on imagery from a wide range of psychological perspectives, including the cognitive. Its journal, Imagination, Cognition and Personality , commenced publication in the early s. The Association may now be defunct — its web site has disappeared — but the journal continues to be published.

    Despite the developments outlined above, interest in imagery amongst experimental psychologists remained at a fairly low level until the mid to late s. It was the recognition, in that period, of the powerful mnemonic effects of imagery that changed the situation, leading to a thriving tradition of experimental research, and securing imagery a firm place in cognitive theory.

    These mnemonic effects, it turned out, could be clearly demonstrated in readily repeatable experiments that did not rely in any way upon introspective reports. According to Bugelski , , an important stimulus to the flowering of experimental research on imagery and memory [ 23 ] was the publication of Frances Yates' celebrated and widely read historical study, The Art of Memory.

    Yates details how imagery based mnemonic techniques, particularly versions of the so-called method of loci , were in widespread use amongst European intellectuals, educators, and orators from classical Greek through to early modern times, and she argues that the knowledge and use of these techniques may have had quite significant effects on the development of Western philosophical, theological, and early scientific thought.

    Shereshevskii's truly prodigious feats of memory were apparently made possible by an abnormally vivid visual imagination, often harnessed to his own version of the method of loci. Turner had formerly worked as a stage magician and memory man, and suggested that the subjects be taught an imagery mnemonic technique to help them to realize the full potential of their memories.

    As a result, however, the experiment was deemed a failure; when the subjects used the mnemonic technique, there seemed to be no practicably measurable limits to their information-storage capacity! Because of this, the study was never published, but word of the findings does seem to have got out, particularly via Eugene Galanter, who had also been at the University of Pennsylvania at the time.

    This book is considered one of the key, foundational works of the cognitive revolution in psychology, and was enormously influential in the field although it is better known for its introduction of concepts from computing and Artificial Intelligence research into psychology, rather than for its account of imagery mnemonics Gardner, ; Hirst, ; Galanter, ; Neisser, p.

    But, almost certainly, the most important figure in the study of the mnemonic effects of imagery was the Canadian psychologist Allan Paivio, whose interest in the subject seems to have originated quite independently of any of the influences mentioned so far, going right back to , when he witnessed an impressive demonstration of the power of an imagery mnemonic, and was taught how to use it, as part of a course on public speaking that he attended Paivio, c, pp.

    The connection between imagery mnemonics and public speaking goes right back to their origins in ancient times: see Supplement: Ancient Imagery Mnemonics. Despite this, perhaps because of the still generally iconophobic character of North American psychology through the s see Supplement: The American Response: Behaviorist Iconophobia and Motor Theories of Imagery , his first publication to very tentatively suggest a role for imagery in memory did not appear until Paivio, The former debate is about the function of imagery in cognition, the latter is about the nature and mechanism of imagery itself.

    The findings of this extensive experimental research program on the mnemonic effects of imagery, can be crudely summarized as the discovery of two principal effects. Secondly, and somewhat more controversially, Paivio and others claim to have shown that imagery plays a large role in verbal memory even when the experimental subjects are not given explicit instructions to form imagery, and make no deliberate effort to do so.

    Once these quantitative imagery values were established, Paivio was able to show, in various experimental designs, that words with high imagery values were consistently remembered significantly better than those with lower ones, quite regardless of any conscious intent on the subjects' part to form relevant images Paivio, , , a. By the end of the s, the work of Paivio and others on the mnemonic properties of imagery had established a strong empirical case for the functional importance of imagery in cognition. The phenomenon could no longer be ignored by psychologists, or treated as a mere subjective epiphenomenon of no scientific interest, as it had been in the Behaviorist era.

    However, this work had done very little to illuminate the nature of imagery itself, or of the cognitive mechanisms that generate it. Kosslyn also demonstrated that the subjective sizes of visual mental images and the relative sizes of their sub-parts measurably affect the times it takes to inspect and report on particular details of imagined objects. The presence of larger features of an object could be reported more quickly from an image of the object than smaller features. As this size-time relation, did not appear unless the subjects used imagery to do the task i.

    It should be noted that the methodology of many of these experiments leaves them vulnerable to the charge, pressed by several critics, that the results reflect not so much the normal workings of cognition, and the properties of the representational structures such as mental images that enable them, but, rather, what psychologists call the demand characteristics of the experimental situation Orne, ; Rosnow, see supplement.

    This is a well-known pitfall of psychological experimentation with human subjects, and experimenters are, for the most part, well aware of it, and take what precautions they can to rule out the possibility that demand characteristics might significantly influence their findings. Nevertheless, certain types of imagery experiment, including most of those discussed in this section, appear to be particularly susceptible to such influence Intons-Peterson, , and it may sometimes be effectively impossible to rule out the possibility that demand characteristics have played a large, or even predominant, role in determining the results.

    Thus, some of the results obtained in this area of research remain open to question. On the other hand, converging evidence from several different types of experiment seems to have been enough to establish a consensus amongst most cognitive scientists that the processes of mental scanning, mental rotation, and the size effects in image inspection are real and significant components of cognition. A lively and high-profile theoretical debate ensued, about the nature of mental imagery and of mental representation in general. The analog-propositional debate , occasionally also called the picture-description debate , or sometimes just the imagery debate as if there were no other debatable or hotly debated issues about imagery is an ongoing and notoriously irreconcilable dispute within cognitive science about the representational format of visual mental imagery.

    The huge impact it had on the early development of the field appears to have resulted in a widespread belief, amongst both philosophers and cognitive scientists, that analog and propositional theories those terms being understood in the rather special senses that they have acquired in this context , together, perhaps, with hybrid theories that claim to incorporate elements of both e.

    That is not the case, as we shall see in section 4. To a first approximation, the analog side of the debate holds that the mental representations that we experience as imagery are, in some important sense, like pictures, with intrinsically spatial representational properties of the sort that pictures have i.

    Mental Imagery and Visual Working Memory

    The propositional side, by contrast, holds the relevant mental representations to be more like linguistic descriptions of visual scenes , without inherently spatial properties of their own. Although it began as a dispute amongst scientists, the debate clearly touches on fundamental issues about the nature of mind and thought, and perhaps the nature of science too, so it soon attracted a good deal of interest from philosophers as well. It is good to be aware that the terms analog and propositional, although they have become entrenched usage in this context, are both potentially misleading.

    On the one hand the propositions which are supposed by some to constitute the descriptions that constitute imagery, are not really propositions at all in the established philosophical sense of the word: rather they are a sort of sentence albeit not sentences natural language, but of mentalese. Although the debate began, and was at its fiercest, during the formative years of the discipline of cognitive science in the s, it has yet to reach a generally accepted resolution.

    However, it may be difficult to understand the scientific and philosophical issues at stake unless one has a sense of the historical and intellectual context in which the dispute originated. Matters became so hotly contested during the s that some participants, most notably Anderson and Palmer b, , came to the conclusion that the disagreement was quite impossible to resolve by the methods of scientific psychology, or perhaps at all.

    Indeed, Anderson offered a formal proof purporting to show that the two main contending theories are empirically equivalent. Anderson's arguments in particular aroused much interest at the time, and were themselves vigorously disputed Hayes-Roth, ; Pylyshyn, b; Cohen, and defended Anderson, However, the main debate continued, and it is probably fair to say that most observers have come to the conclusion that the empirical equivalence claimed by Anderson is ultimately not particularly interesting or important.

    It can probably be regarded as just a special case of the well known Duhem-Quine underdetermination of theory by evidence: many philosophers of science hold that any theory can be made to fit any evidence provided one is allowed freely to supplement the theory with arbitrary and perhaps ad hoc, complex, and implausible auxiliary hypotheses, which is essentially what Anderson was doing.

    Nevertheless, the fact that such claims could be seriously proposed and discussed is testament to just how acrimonious and intractable this debate about imagery had come to seem at the time, and how important it was to those involved. The very possibility of a science of cognition seemed to be under threat. Despite this, the debate's focus has, in practice, been quite narrow. Although it is often understood to be a debate about the nature of imagery per se , it may more truly be seen as about what theory of imagery will best account for the facts within the parameters of a computational functionalist theory of the mind , i.

    Although this computational functionalism still has many adherents, it no longer dominates the philosophy of mind and cognition to the extent that it once did. However, in the early s it was new and exciting, and the computational approach to cognitive theory that it sanctioned was being taken up with great enthusiasm by many psychologists Baars, ; Gardner, Initially, the concurrent rises of imagery research and computational psychology, through the s and into the s, played mutually reinforcing roles within the cognitivist revolution against Behaviorism, because they both implied that the concept of mental representation should play a central role in the science of the mind.

    However, a tension soon became apparent between the symbolic and syntactic concept of mental representation that came from Artificial Intelligence and the, on the face of it, very different concept of representation implicit in the work of the imagery researchers. The analog-propositional debate, and much of the passion and partisanship it aroused, grew out of that tension, and, more particularly, the desire to bring imagery within the fold of computational functionalism. The analog-propositional debate may be said to have begun when this tension found its first clear expression, in a very influential article by Zenon Pylyshyn Although a number of other cognitive scientists and philosophers have taken positions, and made empirical and theoretical arguments, similar to and supportive of those of Pylyshyn e.

    In his article he raised a number of objections to this notion, some of which have withstood criticism better than others, but the underlying worry was clearly that the inner-picture theory of imagery inevitably commits the homunculus fallacy: it implicitly relies on the assumption that there is a little man or rather, something that is the functional equivalent of a full-fledged visual system, including eyes , or, at the very least, something with inexplicable mental powers, inside the head to reperceive, experience, and interpret the image.

    The broad functional architecture of Kosslyn's theory, in fact, closely parallels that of Descartes' account of imagery see section 2. However, their critics remain unconvinced that they have truly even recognized this pitfall, let alone successfully avoided it Slezak, , ; Thomas, b, , , ; Pylyshyn, a,b, a,b,c, , What the program actually does is construct and display a picture on the computer's screen, on the basis of a stored file, and then move it about on the screen in various ways, in order to model some of the ways in which people can supposedly manipulate their mental images such as in mental rotation and mental scanning.

    At the time when the program was written, when computer graphics were in their infancy, and when few people had ever even seen a computer, it may not have been an entirely unimpressive achievement. However, nothing in the program nor, so far as I am aware, in any computer simulation of a pictorial theory of imagery written since implements, or even attempts in any way to simulate or model, a conscious awareness of the pictures. Only the human onlooker consciously experiences the pictures, knows that they are pictures, and can tell what they might be pictures of Thomas, If quasi-pictorial theory were capable of accounting for the representational and conscious nature of imagery without appealing to a homunculus, then the Kosslyn-Shwartz program might constitute a heuristically useful if crude and preliminary model of how images might be built up and transformed.

    However, despite vehement claims to the contrary e. In a subsequent paper, Pylyshyn introduced an important new argument against pictorialism, based on the concepts which he introduced of cognitive penetrability and impenetrability. Cognitive processes are said to be cognitively penetrable if their workings can be affected by the beliefs and goals of the person, and cognitively impenetrable if they cannot be.

    Figure 4. In both cases, the two horizontal lines are the same length, but appear to be different lengths. If that were the case, imagery should be a cognitively impenetrable phenomenon, but it is not. Not only do we have a large degree of voluntary control over the content of our imagery experiences, but it has also been experimentally demonstrated that extra-visual beliefs can influence the course of supposed imagery processes.

    For instance, he holds that if subjects are asked to scan their mental gaze from one point to another on a mental image of a map, what they interpret these instructions to be asking them to do is to behave as if they were actually looking at the relevant map and scanning their gaze between the points. Because they know from their history of ordinary visual experience that it takes longer to scan between points that are further apart, this will be reflected in their performance.

    Thus, the fact that people instructed to scan across their images take longer to scan longer distances is not evidence of the existence of some inner, mental, image-space. Rather, it is a reflection of people's implicit understanding which they may not necessarily always be able to articulate of the visual properties of the actual space around them cf, Morgan, Pylyshyn's critics have often been inclined to conflate his tacit knowledge theory with the view that the results of imagery experiments may be fatally contaminated by the effects of experimental demand characteristics see supplement.

    However, although he clearly does think experimental demand plays a large role in determining many of the results on imagery, he resists this interpretation of his position. He is not saying as is sometimes implied that experimental subjects are, as it were, consciously faking their performances in order to please the experimenter. Rather they are doing their best to comply with experimental instructions that turn upon the slippery concept of mental imagery.

    It is generally assumed that problems caused by demand characteristics can be avoided or minimized by careful and ingenious experimental design, or by such tactics as post-experimental questioning of subjects to see if they have guessed the experimental hypothesis Kosslyn, for one, routinely throws out data from subjects who guess this correctly. Rather, the problem lies with the basic conceptualization of the phenomena and the experimental tasks by experimenter and subject alike.

    Of course, Pylyshyn was far from the first person to raise objections to the idea of inner pictures, or to criticize the standard interpretations of imagery experiments. What made his critique particularly effective was that he began, both in his article and in subsequent writings e. At last, there seemed to be a viable alternative to the pictorial conception of imagery that had dominated folk, philosophical, and psychological thinking about imagery since ancient times.

    Particularly important for Pylyshyn was the work of Simon and Newell , and their students Baylor and Moran , who had already made some progress in devising symbol systems suitable for the computational representation of the spatial structure of simple layouts or objects such as rectangular blocks. They explicitly presented these representations as models of the image representations that people use in doing certain visuo-spatial cognitive tasks.

    In his original article, Pylyshyn alludes to a number of disparate schemes developed by various computer scientists, for the computational representation of visual information, and it is perhaps not altogether clear what these have in common as alternatives to a pictorial conception of imagery.

    The vocabulary and syntax of mentalese if it exists remain unknown, but they are likely to be very different from those of English or any other natural actually spoken language. Nevertheless, Fodor holds that any cognitive theory capable of accounting for the full range of human mental capacities is bound to make appeal to some such inner language. This means, of course, that Pylyshyn's positive view of imagery — description theory — is viable only if the controversial language of thought hypothesis is true.

    However, many of Pylyshyn's objections to pictorial theories of imagery might still stand even if this were not the case. Fodor did not , however, embrace Pylyshyn's objections to pictorial mental imagery. Although he holds that pictorial representations are not sufficient to support cognition on their own, and are probably dependent on associated mentalese representations for playing any cognitive roles that they do play, he nevertheless argues against some philosophical objections to mental pictures, [ 33 ] and thinks that the empirical evidence from psychologists such as Paivio and Shepard suggests that images do in fact play a real role in our cognitive processes Fodor, pp.

    It is sometimes objected that a description theory, like Pylyshyn's, is incompatible with the phenomenology of imagery e. After all, having a mental image of a cat does not seem anything like reciting a description of a cat to oneself. However, this seems to be based on having drawn too close an analogy between the mentalese descriptions intended by the theory and descriptions in English or other natural languages. In the first place, although we can be conscious of English sentences as such, we are pretty much ex hypothesis never conscious of our mentalese representations as such, but only at most of what they represent.

    Thus there is no reason to expect that entertaining a mentalese description would subjectively seem anything at all like reciting, or reading, or otherwise thinking of a description in English. Thus his theory readily accounts for the phenomenological similarity between imagery and perceptual experience. If, as seems likely, the perceptual descriptions are typically more detailed than those of imagery, this might also account for any phenomenological differences between imagery and perception.

    This introspectively based argument against description theory, weak though it is, is often prelude to the even stronger claim that the phenomenology of imagery directly supports the view that mental images are inner pictures. After all, it is said, in contrast to reciting a description to oneself, having a mental image of say a cat does seem very much like seeing a picture of a cat.

    Although some people seem to find this argument tempting e. There is little or nothing to the alleged similarity between the experience of having a mental image of a cat and that of seeing a picture of a cat, apart from the fact that both these experiences in some ways resemble the experience of actually seeing a cat, and both differ from it in that no cat need actually be present.

    Pictures and mental images also differ in important ways. It is generally possible, for instance, to turn over a picture and look at its blank backside, to examine its surface for marks such as scratches or dirt that do not have a depictive role, or to look at its flat surface from an oblique angle so that what it depicts appears distorted.

    You cannot do such things with a mental image. It is true that pictures paintings, drawings, photographs, videos, etc. Indeed, pictures and sculptures may be our only familiar example of this, apart from mental imagery itself. However, it does not follow that mental images must therefore be a species of picture. The easy analogy may be a false one. In fact, neither Paivio nor Shepard, who were undoubtedly the best known imagery researchers at the time Pylyshyn published his initial critique, were committed to the straightforward picture theory of imagery that he seemed to be criticizing.

    Cooper, Neisser developed the notion of imagery as perceptual readiness or anticipation into a theory of imagery explicitly opposed to both the picture and description theories Neisser, , a, b; — see section 4. Finke's experimental work on visual illusions and aftereffects induced by imagery Finke, , ch. Gibson , However, Stephen Kosslyn soon intervened in the debate, proposing a theory of visual imagery that was both explicitly computational and overtly pictorialist or, as he prefers, quasi-pictorial , based on an analogy with computer graphics programs which were a fairly new thing back then Kosslyn,