Most of the material below comes from a long post that I made (on Sat, 22 Dec 2001) to the Psyche-D (theoretical issues of consciousness research) email discussion forum. I was replying to some questions asked in the forum by John Preston. There used to be a direct link from this site's home page to the relevant page in the online archives of Psyche-D, but the forum itself was closed down in October 2007, and the archives nowappear to have become unavailable. Luckily, though, I kept a copy of my post, which a number of people seem to have found interesting, and am able ressurect it here. My views on this matter, however, have changed somewhat since 2001. Largely thanks to the work of Zeman et al. (2010), but also to the testimony of numerous non-imagers who have contacted me online, I am now a bit less skeptical about non-imagers than I was back then.
To the best of my knowledge, with the exception of Galton's original work (1880, 1883), Sommer's brief case study (1978), Faw's (1997, 2009) articles (discussed in the addendum, below), and a few paragraphs in chapter 3 of Schwitzgebel's (2011) book, this is the only really substantial discussion of the phenomenon of non-brain-damaged "non-imagers" available anywhere.
The passages in dark red are Preston's questions, as I quoted them in my reply. Apart from updating the links and references, where needed, and adding one or two minor clarifications (in square brackets and in green), I have not done anything to change the substance of what I wrote in 2001. However, I have since added an addendum, at the bottom of the page, in green, detailing and discussing a few pieces of relevant information that have appeared (or come to my attention) since that time. (Since 2007, when the first version of the addendum appeared, it has been added to and revised a number of times. - N.J.T.T.
John Preston wrote:
I'm aware of the existence of a large amount of recent research, from a cognitivist point of view, on mental images. But does anyone know: (i) whether there are people who claim not to have mental images (not just visual images) at all?
If complete non-imagers (who are otherwise normally conscious and mentally competent) really could be proven to exist, that would be of great theoretical importance. At least since the time of Aristotle (see De Anima 431a 15-20), it has been very widely held (by both theoreticians and "the folk") that the experience of thinking consists largely or entirely in the vicissitudes of mental imagery, although it has long been clear, from consideration of the mental abilities of the congenitally or long-time blind, that it is not essential that any of this imagery be visual (even in the sighted other imagery modes may be more important than is commonly realized (Newton, 1982), and verbal imagery, in particular, plausibly plays a very large role in most human thinking (Paivio, 1971, 1986)). Of course, Cognitive Science has by now provided us with a rich set of alternative accounts of the underlying mechanisms of thought - of what might be going on under the surface, as it were - but it is not clear that even now we have any developed alternative account of the conscious experience of thinking available to us. When contemporary cognitive scientists come to consider conscious thought rather than underlying mechanisms, they return to the idea that it is embodied in imagery (e.g. Damasio, 1994). The utopian fantasies of the Churchlands notwithstanding, I do not believe that there is anyone who seriously claims to be directly conscious of their thinking as being embodied in mentalese, or weight space vectors, or patterns of neuronal excitation, or any of the other sorts of cognitive mechanisms that are discussed. (Theorists like Mangan (2001), James (1890), and the Wurzburg school psychologists (Thomas, 2001) may or may not be right to hold that not all aspects of the conscious experience of thinking can be characterized in terms of imagery, but I do not think they are arguing that it imagery is not an essential component of conscious thought.) If true and total (and mentally competent) non-imagers really exist, then the imagery theory of conscious thought would be refuted. I suspect something like this consideration is what motivates John Preston's question.
Certainly it is largely for this reason that I have taken a considerable interest in the issue of "non-imagers" over many years now. Unfortunately, so far as I have been able to discover (and I have looked, and have asked those who might be expected to know), although the existence of people who deny having visual imagery has been known to science for well over 100 years (Galton, 1880, 1883), no systematic research whatsoever has been done on the phenomenon. I have not even been able to find any reliable figures for the incidence in the general population of visual "non-imagers" (Abelson (1979) quotes a figure of 10-12% , but gives no hint of where this figure comes from - if anyone knows of a better source on this point, please let me know!). Furthermore, even the rare anecdotal accounts of "non-imagers" that I have found in the scientific literature seem to focus almost entirely on visual imagery. This may be largely because "imagery" is often understood as meaning visual imagery, both by scientists and by ordinary folk. Although psychologists will sometimes talk about auditory imagery, haptic imagery, "motor imagery" and the like, it is not obvious that this accords with ordinary usage very well. (Scientific studies of any sort concerning non-visual imagery, although they do exist, are quite thin on the ground.)
There are accounts in the neurology literature of people who have apparently retained their vision but lost their ability to experience visual mental imagery after brain damage, but of course, these people are mentally impaired in other, usually more obvious, ways. (I could dig out some references for you if you want, but I am not aware of any neurological case studies of people who have lost imagery in another sense mode. See Richardson (1999 ch.2) for a brief and selective literature review.) Inevitably, however, introspective phenomenological reports from brain damaged subjects need to be treated with great caution. For reasons to be explained below, introspective reports on these sorts of matters are very problematic to evaluate even for neurologically healthy subjects. Clearly things are much worse when dealing with the brain damaged, who may often suffer subtle and not-so-subtle language deficits, and who, in some cases, will insist they can see perfectly when they are clearly blind (Anton's syndrome - Young & de Haan, 1990), will insist they are blind when they can clearly see (Hartmann et al., 1991 [This is not the now well-known blindsight syndrome. This is a man who, although certainly visually impaired, rides a bicycle in the streets and writes and uses shopping lists, but still insists he can see nothing.]) or will deny the fact that they are paralyzed (anosognosia - Ramachandran, 1995).)
Apart from such neurological cases, however, anecdotal accounts of non-imagers in the psychology literature not only seem to confine themselves to the visual mode, they also raise doubts about the reality (or stability) of the phenomenon. It appears that on more probing questioning such people will generally admit to experiencing at least some visual imagery, particularly in dreams (Galton, 1880, pp. 305-306; Galton, 1883, pp. 91-92; Marks, 1972, p. 107; Sommer, 1978, chap. 7). David Marks, who is very arguably the leading contemporary researcher into individual differences in the conscious experience of visual imagery has even suggested to me (personal communication[; also Marks, 1986 p. 237]) that non-(visual)-imagers may be suffering from some sort of sub-clinical neurological disconnection syndrome, whereby they do have visual imagery, but are unable to report it.
I can add something to this anecdotal evidence, because I have been running a web site devoted to the cognitive science of mental imagery since 1997, and over that period I have received a number of email messages, and, latterly, message board postings, from people who say they lack imagery (by which they seem to mean visual imagery). I have attempted, sometimes with some success and sometimes not, to engage these people in a dialogue about their condition, although I have not always been able to get very clear answers, and in some cases, like Marks and Sommer, I have found that they backpedal on their claims somwhat when pressed. However, I have also noticed that some of these people seem to be quite concerned about their condition, and to be looking for a "cure" - they seem to believe that lack of imagery renders them less imaginative, or something like that. Others seem to be quite content with, or even proud of their condition. I even recently heard from someone who claims that the condition runs in their family. (For reasons that should become apparent below, I do not think this necessarily implies that it is a genetic condition; it might be something more like a family tradition.) One particularly interesting case was a psychology student, Carlos, who had just recently realized that most other people believe they experience visual imagery. He was quite excited, thinking he might have discovered in himself a phenomenon new to science, until he came across the material on my web site. I managed to get more feedback from him than from most of the other cases I have encountered, and did manage to ascertain that he does experience imagery in non-visual modes: he "hears" tunes in his head, for instance. However, on asking about how his thought processes subjectively seem to him (particularly thinking about spatial relations, or remembering the appearance of things) I was not able to get anything much more revealing from him that the claim that he "thinks in concepts" and that he knows what things look like (which is no doubt true, but did not much enlighten me). Some of my other exchanges with non-imagers can still be found online on the back pages of my web site message board at http://forum.asiaco.com/im-im/ [sorry, this board no longer exists]. One topic pursued there is how people who claim that they experience visual imagery only in dreams remember (without waking imagery) that they do have the imagery in their dreams. I cannot, however, recall ever managing to elicit a clear declaration from anyone that they lack imagery in all sensory modes.
Nevertheless, I am fairly confident that, if you searched diligently, and phrased your questions artfully, you could find people who would claim that do not experience imagery of any sort whatsoever. Some might even insist on the point quite vehemently. The trouble is, all such introspective reports about personal, idiosyncracies of subjective experience need to be treated with great caution. We should be wary of resting very much theoretical weight upon them (which is not to say that they should be disregarded altogether). Although, no doubt, there are real differences between different people's subjective lives, there is also much reason to believe that introspective reports about such matters are strongly influenced by cultural forces and by theoretical preconceptions (whether coming from formal psychological theory, "folk" psychological tradition, or even personal pet theories) about what subjective experience ought to be like. Psychodynamic or emotional factors may well also significantly affect these reports: perhaps some people "repress" their imagery experience (in a more or less Freudian sense), but does that mean that they do not have such experience, or just that they do not like to talk or even think about it?
As evidence for the influence of theoretical factors, consider the fact that J.B. Watson, before he developed his Behaviorist metatheory (until at least late 1908), was insisting that his "centrally aroused visual sensations [i.e., visual mental images] were as clear as those peripherally aroused" (Watson, 1913 n.7), but by 1913, when he published his famous Behaviorist manifesto, he was questioning, and soon after outright denying, the very existence of imagery (Watson 1913a, 1913b), eventually stigmatizing the very concept as "sheer bunk" (Watson, 1928) and "medieval" superstition (Watson, 1930). I have discussed the circumstances surrounding this rather radical change in Watson's claims about his own subjective experience, and the reasons for it (including the conceptual confusions that seem to be involved), in an article I published some years ago (Thomas, 1989). It would be implausible to ascribe it either to dishonesty on Watson's part (suppressing subjective evidence that contradicted his new theory) or to an actual change in the workings of his mind; rather what we see here is a rather stark exemplification of how theoretical ideas about psychological matters can radically shape how we conceptualize and report upon our subjective experience.
Of course, Watson's (later) views were very influential, or, at least, he was riding the crest of a wave of historical intellectual change. The abrupt change in Watson's claims about his subjectivity would soon be mirrored in the psychological profession as a whole, and subsequently in allied disciplines. It was also foreshadowed (and partly caused) by the "imageless thought controversy" which raged amongst the introspective psychologists during the first decade of the 20th century (Thomas, 2001). On one side (to simplify the story somewhat) were Oswald Külpe and his students in Würzburg, Germany, and on another we find Edward Titchener and his students at Cornell. Although the Würzburg introspectors did not deny that they experienced mental imagery, they insisted that they also experienced other types of conscious contents (designated by jargon terms such as bewusstseinslagen, but rather vaguely described as, for example "an impalpably given knowing"), the Cornell introspectors categorically denied that such "imageless" contents existed, and insisted that more careful introspection revealed fleeting (perhaps non-visual) imagery or subtle bodily sensations in their place. Needless to say, the results obtained in each laboratory fitted very nicely with the theoretical commitments of the respective presiding professors. This fact did not go unnoticed, and contributed significantly to the loss of confidence in introspective methods, the concomitant decline in scientific interest in imagery, and (in America) the rise of Behaviorism.
Between about 1920 (in the wake of the imageless thought controversy and Watson's polemics) and 1960 I think you would have been hard pressed to find an experimental psychologist in the U.S.A. who would admit to experiencing vivid and copious imagery, and probably a very high proportion would have denied experiencing any sort of imagery whatsoever (with the possible exception of "inner speech"). In the years since the 1970s, and a fortiori before about 1913, when a "non-imager" could scarcely have functioned as a psychologist, you would certainly find things quite otherwise (Holt, 1964; Kessel, 1972; Thomas, 1989, 2001, 2003).
There is evidence for a similar historical pattern, but displaced a few decades forward, amongst both 20th century philosophers and literary critics. Heil (1998 p. 213), notes that contemporary philosophers are very much "inclined to downplay the significance of imagery. . . . In discussions of mental imagery, it is common for discussants to claim that their imagery is dramatically attenuated, or even altogether absent. (In some quarters a professed lack of imagery is worn as a badge of honor.)" (This anecdotal evidence of Heil's certainly jibes with my own experience, and may be further supported by a much earlier anecdote from Price (1953 p. 234).) As Heil is well aware, contemporary philosophers, in this regard, are at odds not only with "the folk", but with nearly all philosophers of previous ages, who regarded imagery as a crucial aspect of cognition (Thomas, 1997, 1999b, 2001, 2003; see also Brann, 1991; Jay, 1993). In Heil's view, rather than reflecting a true difference in subjective experience between contemporary philosophers and earlier ones (and most of 'the folk'), these informal introspective reports are actually much more the result of "what psychologists call a criterion difference, a difference in what we take to constitute imagery". (For the literary critics, see Esrock (1994) and, as evidence of a nascent return swing of the pendulum, Scarry (1999).)
It is not, I think, plausible to believe that these historical changes (within particular intellectual milieux) in what is informally said about said about the mind's contents, reflect actual fundamental changes in everyone's cognitive mechanisms. Nor is it reasonable to think that people were being widely and systematically dishonest in describing their inner experience during one or other of these periods, hypocritically conforming to what they thought would be acceptable to their peers. It is much more plausible to believe that they reflect changes in how the people concerned were inclined to conceptualize their minds' workings, and, thus, to describe them verbally, to themselves as well as to others. I see no reason to think that lay-people cannot be similarly affected by theoretical ideas of a less formal sort (and acquired in less systematic ways).
Weight is added to these speculations by the work of Schwitzgebel (2002a), who has noted a rather similar phenomenon in reports of dreaming. In the 1950s it was widely reported by psychologists that a majority of people's dreams were largely or entirely without color: they were experienced in monochrome. More recent evidence, from the 1960s and later, indicates to the contrary that most people believe themselves to dream in color. It seems fairly clear that this change was not a result of changes in the way people's brains function, but rather to changing cultural influences affecting how they conceptualize and report their subjective experience (and perhaps in how psychologists question them and interpret their answers). The cultural change that Schwitzgebel points to is the prevalence of black and white television in the period when dreams seemed to be in black and white, and its later replacement by color television. I would suggest that other factors may have been at work as well, including the generalized iconophobia of the still deeply Behavioristic American psychology of the 1950s, which had probably seeped somewhat into the popular mind as well.
Schwitzgebel also argues explicitly (2002b) that we really do not know much about what our own mental imagery is like. I find the position as he states it rather extreme and paradoxical, but his arguments certainly lend weight to the view that I have been arguing that we are really not very good at accurately reporting what our private subjective experience is like. Just because it is private, it is hard to be sure that we are applying the words we use to describe it in the same way that the next person does. In attempting this difficult descriptive task we are inevitably affected by our formal or informal theoretical conceptions of how the mind works.
Indeed, if we did not have some such theoretical preconceptions it is questionable whether we would be able to describe the contents of our consciousness at all. The language in which we describe our subjective experience derives entirely, or almost so, from our theories; after all, one could hardly build up a vocabulary for discussing private experience via ostensive definition. Although I think it is mistaken (Thomas, 1999a), the traditional inner 'picture' theory of visual imagery that is entrenched in 'folk' psychological thinking has perhaps served a useful purpose over the centuries by giving people a certain confidence that they are talking sense when they talk about visual imagery experience. At the very least it has given them a vocabulary for talking about such experiences. It is no coincidence, I think, that the reluctance of so many mid-to-late 20th century philosophers to admit to experiencing imagery has gone along with a widespread rejection of picture theory (following the work of Ryle and Wittgenstein) coupled with the absence (at least before Pylyshyn came along) of any clear and convincing alternative explanation of quasi-perceptual experience. The absence of any traditional equivalent to picture theory for explaining quasi-perceptual experience in the other sense modes may go some way towards explaining why non-visual imagery is relatively rarely discussed.
I should probably add, at this point, that the fact that I believe that although I believe that people's attempts to describe idiosyncratic aspects of their imagery experience are thoroughly "theoretically infected", it does not follow that there is no real phenomenon behind them. The eliminativist line taken towards imagery by psychological and philosophical behaviorists has long since proved itself quite inadequate not only to accounting for people's actual subjectivity, but also to accounting for what is now a large and diverse arrary of experimental findings that demonstrate the cognitive effects of imagery: the powerful mnemonic effects of imagery (Paivio, 1971, 1991) probably remain the most important in this regard, but a wide range of other findings (see Finke, 1989; Richardson, 1999) also bear out the point. (Pylyshyn's well known arguments do not, and are not intended to, controvert this. Pylyshyn frequently makes it quite clear that he fully accepts that people have quasi-visual experiences of the sort colloquially called imagery, and he also holds that the representations that embody this imagery have an important functional role to play in cognition. What he is rejecting is merely the view that such representations are in any meaningful sense similar to pictures.)
(ii) whether any psychologists, save for the most radical behaviorists, deny either that people have mental images, or that mental images can serve to produce or guide behavior (as goals, for example)?
The only significant psychologist that I know of who explicitly took such a position was J.B. Watson (see above for references); and even he hedges in places. There probably were other Behaviorists who made similar remarks, but as Glen Sizemore quite rightly points out, even so radical a Behaviorist as B.F. Skinner acknowledged the reality of "private seeing", although, of course, he was unwilling to call it mental imagery, and I do not believe he accorded it anything like the same sort of functional importance that it had for most cognitive theorists (philosophers and psychologists, from Aristotle to Hume to Bergson, Wundt, and Titchener) before the Behaviorist revolution. The iconophobia of the Behaviorist era, which still lingers on in an attenuated form in philosophy and much of cognitive science, is not so much a matter of the explicit denial of the existence or even the importance of imagery; it is simply a matter of ignoring the phenomenon as far as is possible, and treating it as trivial when it cannot be ignored.
(iii) where I might find good literature on questions like this.
As Preston is probably well aware, the literature of the well known "analog/propositional" debate, as discussed in the collections edited by Block (1981a, 1981b), by Tye (1991), and in many publications by Pylyshyn, Kosslyn, Anderson, and others (for further citations see Thomas, 1999a, 2001), is almost totally irrelevant to the questions he asked (and to the issues that I suspect motivate them). Despite its fame and its complexities, this debate was, to all intents and purposes, focused on an extremely narrow issue. It was about what sort of computational (or, latterly, neurological) mechanisms would best reconcile the phenomenological and experimental data about imagery with the computational-functionalist view of the nature of the mind. Kosslyn, Pylyshyn, Anderson, Shepard, Block, Tye etc. are concerned with the nature of the cognitive mechanisms that give rise to mental imagery, and only very indirectly, if at all, with the issues that Preston's questions raise, about individual differences in the conscious experience of imagery, and the functional role of imagery (as consciously experienced) in our thought processes. (In my view the phenomenological and experimental data about imagery cannot be reconciled with a computational-functionalist view of the mind, and thus both the "quasi-pictorial" and the "propositional/descriptional" theories of imagery are false and need to be replaced by a "perceptual activity" account which is not dependent upon functionalist token-token identity theory, but that is another story (Thomas, 1999a).)
In fact, I do not think there is any literature that is entirely on point for Preston's first question. Indeed, there is not much literature on (non-brain damaged) "non-imagers" at all. However, Thomas (1989) does provide a historical case study and theoretical discussion of the matter, and Galton (1880, 1883), Marks (1972), and Sommer (1978, chap. 7) provide anecdotal accounts of non-(visual)-imagers. If anyone is sufficiently intersted, I can supply a copy of the online exchange I had with Carlos the non-imaging psychology student (it was conducted publicly, on a now defunct web message board). See Richardson (1999 ch.2) for the brain damaged cases.
I think that is pretty much it for "non-imagers". However, there is extensive work on less radical individual differences in imagery, particularly on reported vividness differences (see Marks (1999) and Richardson (1999) for recent reviews). Also, I believe that research on different peoples' preferred imagery mode (visual, auditory, motor, etc. - what was known as "imagery type") was quite extensively pursed in the early years of the 20th century. I do not have the references for that at my fingertips, but Schlaegel (1953) might provide a place to start looking. [Even better places would be Angell, (1906 ch. 8) and Fernald (1912). However, the theory of imagery types was later discredited, in the eyes of most psychologists, by Thorndike (1914 ch. 16) and Griffits (1927).]
For the essentially negative answer to the second question, see Thomas (1989, 2001, 2003, 1999b 1997), McMahon (1973) and perhaps Brann (1991).
I'm sorry for having gone on so long, especially as I am probably not giving Preston the answer he was hoping to hear, but it is so rare to come across someone who realizes the theoretical significance of this topic. I only wish that there were some substantial empirical work on non-imagers available. Does anyone have a grad student in search of a research project?
Abelson, R. P. (1979). Imagining the purpose of imagery. Behavioral and Brain Sciences, 2, 548-549.
[Angell, J.R. (1906). Psychology: An Introductory Study of the Structure and Function of Human Consciousness (3rd edn.). New York: Henry Holt and Co.]
Block, N. (Ed.) (1981a). Imagery. Cambridge, MA: MIT Press.
Block, N. (Ed.) (1981b). Readings in Philosophy of Psychology, Vol. 2.London: Methuen.
Brann, E.T.H. (1991). The World of the Imagination: Sum and Substance.Savage, MD: Rowman & Littlefield.
Damasio, A.R. (1994). Descartes' Error: Emotion, Reason, and the Human Brain. New York: Putnam.
Esrock, E.J. (1994). The Reader's Eye: Visual Imaging as Reader Response. Baltimore, MD. Johns Hopkins University Press.
[Fernald, M.R. (1912), The Diagnosis of Mental Imagery, Psychological Monographs (14 #1) Whole No. 58.]
Galton, F. (1880). Statistics of mental imagery. Mind, 5, 301-318.
Galton, F. (1883). Inquiries into Human Faculty and its Development.London: Macmillan.
[Griffits, C.H. (1927). Individual Differences in Imagery. Psychological Monographs (37 #3) Whole No. 172.]
Hartmann, J.A., Wolz, W.A., Roeltgen, D.P., & Loverso F.L. (1991). Denial of Visual Perception. Brain and Cognition, 16, 29-40.
Heil, J. (1998). Philosophy of Mind. London: Routledge.
Holt, R. R. (1964). Imagery: The return of the ostracized. American Psychologist, 19, 254-266.
James, W. (1890). The Principles of Psychology. New York: Holt.
Jay, M. (1993). Downcast Eyes: The Denigration of Vision in Twentieth-Century French Thought. Berkeley, CA: University of California Press.
Kessel, F.S. (1972). Imagery: A Dimension of Mind Rediscovered. British Journal of Psychology, 63, 149-62.
Mangan, B. (2001). Sensation's Ghost: The Non-sensory 'Fringe' of Consciousness. Psyche , 7. URL: http://www.theassc.org/files/assc/2509.pdf
Marks, D.F. (1972). Individual differences in the vividness of visual imagery and their effects. In P. W. Sheehan (Ed.), The Function and Nature of Imagery (pp. 83-108). New York: Academic Press.
[Marks, D.F. (1986). The Neuropsychology of Imagery. In D.F. Marks (ed.). Theories of Image Formation (pp. 225-241). New York: Brandon House.]
Marks, D.F. (1999). Consciousness, Mental Imagery and Action. British Journal of Psychology, 90, 567-585.
McMahon, C.E. (1973). Images as Motives and Motivators: A Historical Perspective. American Journal of Psychology, 86, 465-490.
Newton, N. (1982). Experience and Imagery. The Southern Journal of Philosophy, 21, 475-487.
Paivio, A. (1971). Imagery and Verbal Processes. New York: Holt, Rinehart and Winston. [Reprinted in 1979 -- Hillsdale, NJ: Erlbaum]
Paivio, A. (1986). Mental Representations: A Dual Coding Approach. New York: Oxford University Press.
Paivio, A. (1991). Dual Coding Theory: Retrospect and Current Status. Canadian Journal of Psychology, 45, 255-287.
Price, H.H. (1953). Thinking and Experience. London: Hutchinson.
Ramachandran, V.S. (1995) Anosognosia in Parietal Lobe Syndrome, Consciousness and Cognition, 4, 22-51.
Richardson, J.T.E. (1999). Mental Imagery. Psychology Press: Hove, U.K.
Scarry, E. (1999). Dreaming by the Book. Princeton NJ; Princeton University Press.
Schwitzgebel E. (2002a). Why Did We Think We Dreamed in Black and White? Studies in History and Philosophy of Science, 33, 649-660. Online at http://www.faculty.ucr.edu/~eschwitz/SchwitzAbs/DreamB&W.htm
Schwitzgebel E. (2002b). How Well Do We Know Our Own Conscious Experience? The Case of Imagery. Journal of Consciousness Studies, 9, 35-53 Online at http://www.faculty.ucr.edu/%7Eeschwitz/SchwitzAbs/Imagery.htm
Schlaegel, T.F. (1953). The Dominant Method of Imagery in Blind as Compared to Sighted Adolescents. Journal of Genetic Psychology, 83, 265-277.
Sommer, R. (1978). The Mind's Eye. New York: Delacorte Press.
Thomas, N.J.T. (1989). Experience and Theory as Determinants of Attitudes toward Mental Representation: The Case of Knight Dunlap and the Vanishing Images of J.B. Watson. American Journal of Psychology, 102, 395-412. [Available online at http://www.imagery-imagination.com/dun-wat.htm ]
Thomas, N.J.T. (1997). A Stimulus to the Imagination. Psyche , 3. On-line serial, URL: http://www.theassc.org/files/assc/2287.pdf [PDF download]
Thomas, N.J.T. (1999a). Are Theories of Imagery Theories of Imagination? An Active Perception Approach to Conscious Mental Content. Cognitive Science, 23, 207-245. [Available online at http://www.imagery-imagination.com/im-abs.htm ]
Thomas, N.J.T. (1999b). Imagination. In C. Eliasmith & Eric Hochstein (Eds.) Dictionary of Philosophy of Mind. Online publication. URL: https://sites.google.com/site/minddict/imagination
Thomas, N.J.T. (2001). Mental Imagery. In E. Zalta (Ed.). The Stanford Encyclopedia of Philosophy. Online publication. URL: http://plato.stanford.edu/entries/mental-imagery/ [Current, updated version, 2010]
Thomas, N.J.T. (2003). Imagery, Philosophical Issues about. In L. Nadel (Ed.) Encyclopedia of Cognitive Science. London: Macmillan/Nature Publishing. [Penultimate draft online at http://www.imagery-imagination.com/mipia.htm]
[Thorndike, E.L. (1914). Educational Psychology (Volume III). New York: Teachers College, Columbia University.]
Tye, M. (1991). The Imagery Debate. Cambridge, MA: MIT Press.
Watson, J.B. (1913a). Psychology as the Behaviorist Views It. Psychological Review, 20, 158-177. [Available online at http://psychclassics.yorku.ca/Watson/views.htm]
Watson, J.B. (1913b). Image and Affection in Behavior. Journal of Philosophy, Psychology and Scientific Methods, 10, 421-8.
Watson, J.B. (1928). The Ways of Behaviorism. New York: Harper.
Watson, J.B. (1930). Behaviorism (2nd ed.). Chicago: University of Chicago Press.
Young, A.W. & de Haan, E.F. (1990). Impairments of Visual Awareness. Mind and Language, 5, 29-48.
Nigel J.T. Thomas Ph.D.
The paragraphs below discuss further information on the topic of non-imagers that has appeared, or has come to my attention, since the above post was written in 2001. Unfortunately, it only serves to make it even more clear how little is understood about the matter.
(i) Burbridge (1994) has examined Galton's private papers, and from them is able to fill in many details of Galton's researches on mental imagery, and to give a much more complete account of them than is available from Galton's own publications (1880, 1883). (Amongst other things, Burbridge is able to identify most of the individual "distinguished scientists" and other intellectuals who responded to Galton's questionnaire on imagery, and to tell, at least in general terms, and sometimes more specifically, how each of them actually responded.) This is important because not only was it Galton's work that first brought the possibility that some people might lack imagery to scientific and scholarly attention, but it is still by far the best known account of the phenomenon. Much weight has been put upon Galton's brilliant and pioneering research, but it is not without its flaws. Galton's own claims are often stronger than the data seem to warrant, and sometimes secondary accounts based on his work exaggerate them further.
(ii) Brewer & Schommer-Aikins (2006) re-analyzed Galton's original data and also attempted to replicate his findings on the imagery of scientists with a new study closely based on his original design. They found that neither Galton's original data nor their own results supported Galton's (1880, 1883) well known claim that scientists are more likely than other people to be non- (or very poor) imagers. Galton appears to have mis-analyzed his own data, and Brewer & Schommer-Aikins, in their own study, found "no scientists totally lacking in visual imagery and very few with feeble visual imagery." Galton's sample does seem to have included a handful of individuals claiming to have no visual imagery whatsoever (see iii below), but his data certainly do not justify the oft repeated conclusion that this condition is common amongst scientists. Brewer & Schommer-Aikins (2006) provide many examples of published second-hand reports of Galton's claims about the imagery of scientists (and we can add to their list, Sommer (1978 p. 1)). Often, these do not just repeat Galton's erroneous conclusion, but state it in considerably stronger terms than he did.
(iii) Kosslyn (1980 p. 399) says that, according to Galton, non-imagers form "slightly over 10 percent" of the general population, and in a later work (Kosslyn, 1983 p. 195) this figure has risen to "about twelve percent." It seems likely that Abelson (1979) got his figure of 10-12% from the same source. A. Richardson's book Mental Imagery (1969 p. 129) also quotes the 10% figure, but ascribes it to a brief 1963 article in The Mensa Correspondence (51, pp. 1-5), by McKellar. I have made some efforts to get hold of a copy of this, but without success. (If anyone has a copy of it, or knows where one might be found, please let me know.) But, in any case, I would be quite suprised if McKellar's figure does not turn out to derive from Galton again.The trouble is that it looks to me as though these numbers are all based upon a flawed reading of Galton's findings (no doubt having been misled by Galton's own inaccurate acount of his results, as detailed by Brewer & Schommer-Aikins (2006)). In fact Galton initially seems to have categorized some 13 of his sample of 100 "distinguished men" (scientists and others) as having "very dim" imagery (Burbridge, 1994 p. 455). There was no "no imagery" category in his data analysis, and although it appears that the "very dim" group did include some individuals reporting having no visual imagery whatsoever [H. Lefoy and C.P. Smyth (Burbridge, 1994 p. 460), and probably also G.W. Romanes and John Herschel (Brewer & Schommer-Aikins, 2006), and possibly more], it is clear from some of the actual responses quoted in Burbridge's article that Galton also included several respondents in this group who by no means denied all experience of imagery. Also, of course, Galton was very far from suggesting that this sample of 100 deliberately chosen men of outstanding intellectual achievement was typical of the general population, and he makes it clear that there were fewer (if any) non-imagers in the other more representative samples he polled. To be fair to Kosslyn, his 1983 discussion also made it quite clear that he had grave doubts as to whether non-imagers were in fact as common in the 1980s as (he thought) Galton had found them to be in the 19th century, and in a recent online interview Kosslyn (2002) has asserted that “less than 2 percent” of the modern population are non-imagers. However, he gives no indication whatsoever of the source of this latter number, and I have not found any mention of it in any of his more formally published writings, so it can hardly be regarded as reliable. I suspect it is no more than an informed "guesstimate." (Although Kosslyn, who by 2002 had already devoted about 30 years of his life to researching and, one may presume, talking to people about, mental imagery, is surely in a better position to make such an informal estimate than almost anybody else.) Much the same can be said for the figure of "probably less than 5%" given by Faw (1997). (But see the remarks about Faw's more recent (2009) claims in §vi below.). Although he mentions not only Galton's (1880, 1883) study, but also Betts' (1909) more extensive early research on individual differences in imagery, and unpublished work of his own, it is not clear that he is even claiming that any of these provide direct support for the "less than 5%" figure.
Betts (1909), does provide a number of tables showing percentages of instances where people reported that they had "no image." On page 15, indeed, he gives a figure of 10% (of a group of 45 Cornell College students) reporting no visual image. (Betts looked at six other modalities besides the visual, and reports different numbers for these.) This may, then, be another source for the commonly quoted 10% figure (although Betts is rarely explicitly cited in its support).
There are two problems with this however. First of all, Betts got wildly varying figures with different groups he tested. Among two other groups of students he found only 2% of reports of "no visual image," whereas amongst a group of "trained psychologists" (18 professors and assistants, mostly from Columbia University) he found a full 19% of such reports! But, more importantly, these numbers do not refer to individuals who were unable to experience visual images at all. Betts provided his subjects with a lengthy and elaborate questionnaire that asked them to imagine a large number of specific things, and particular aspects of those things, such as color, form, distance, brightness, etc., and then, in each case, to provide vividness ratings (ranging from "perfectly clear and vivid as the actual experience" to "no image present at all, only knowing that you are thinking of the object"). Thus, it is not the case that 19% of the 18 psychologists tested (that would be 3.42 psychologists!) said that they never experienced visual imagery. Rather, the psychologist subjects reported that, in 19% of their attempts, they could not get the particular image (or image aspect) that was being requested (and similarly with the students who were tested). Probably, even people who commonly experience vivid imagery cannot always conjure up a particular requested image on demand. Thus, because of the way he analyzed and presented his results, Betts provides no evidence whatsoever that any of his experimental subjects, even amongst the psychologists, were non-imagers.
fact, with so little real research available on non-imagers, the topic of their
incidence in the general population has degenerated, even in the peer reviewed
scholarly literature, into a game of Chinese Whispers. Berman & Lyons (2007),
for example, cite Brann (1991) as authority for their claim that "contemporary
that about 2% of the general population are non-imagers.* In fact, Brann (1991
p. 355) gives a figure of 3%, citing Kosslyn (either 1980 or 1983 – it
is not clear which) as her source. In fact, as just discussed, Kosslyn gives
figures of 10% and 12% respectively in those works. Brann may be misunderstanding
a passage where Kosslyn (1983 p. 195) mentions (but does not properly cite!)
a study that apparently found that 97% of a sample of Mensa members
claimed to have "vivid imagery." It
does not, of course, follow (and I do not think Kosslyn means to imply) that
the other 3% had no imagery at all (and, of course, Mensa members
facto, psychologically atypical of the general population).
*I have reason to believe that Berman & Lyons actually arrived at their 2% figure thanks to a misunderstanding of a communication from me. An earlier draft of their paper, that I critiqued for them, had 3%, as given by Brann, and in my commentary I questioned this, and mentioned Kosslyn's (2002) figure of 2%. However, the published version of their paper attributes the 2% figure to Brann, not Kosslyn. Wherever the number comes from, they are certainly being misleading in implying that it represents some sort of consensus.
(iv) Berman & Lyons (2007) have recently re-examined the historical evidence relating J.B. Watson's denial of the existence of mental imagery, which played an important role in the crystallization of his enormously influential Behaviorist approach to psychology. For the most part, their paper reiterates and reinforces the account of this affair that I published several years ago (Thomas, 1989). In particular, they agree that despite his public and sometimes vehement denial of the very existence of imagery from about 1912 onwards, Watson was not a non-imager. Rather, he was motivated to deny its existence by his strong theoretical commitments. Berman & Lyons (2007) do not think Dunlap's views on imagery had quite as much influence on the development of Watson's views as I suggested, and they give an account slightly different from mine of how and why Watson managed to persuade himself that his own imagery was unreal. However, although Watson may well have suffered from the "ideological blindness" that they ascribe to him, I am not persuaded that it would have been sufficient to lead him to deny his own direct experience in the way he seems to have done. It seems to me that something like the conceptual confusions that I ascribed to him in my article (Thomas, 1989) must almost certainly have also played a role.
(v) I have had several more email and message board communications from non-imagers since making the posting to Psyche-D. Some seemed to be offended by the Psyche-D post, taking it to be casting doubt on their veracity or mental competence, which was certainly not my intention. On the other hand, rather to my surprise, at least one of them seemed to like Marks' suggestion (mentioned above) that the non-imagers might really have imagery but, because of some sub-clinical disconnection lesion in the brain, are not able to consciously access it. She thought this did seem consistent with her introspections. Unfortunately her post to my message board at asiaco.com was lost when that board went dark, but as I far as I can remember she said something to the effect that it sometimes felt as though she was experiencing imagery, but it was somehow hidden behind a screen or veil. I am not sure what to make of this, but it is probably the most interesting introspective report on the topic that has come my way.
I wrote the above, I have come across two papers by Faw (1997, 2009) that directly
and centrally addresses the issue of non-imagers. Unfortunately the first contains
no new empirical data, and although the second mentions a survey of 2,500
people carried out by Faw himself, and appears to claim (the language is somewhat ambiguous) that between 2% and 5%
of them claimed to be non-imagers, only very sketchy details are given of the
methodology and the results, which does not give me much confidence in it.
Faw is apparently a non-imager himself, so he can add something to the store
of anecdotal evidence, and it certainly helps that he is able to interpret his
introspections in the light of the relevant psychological and neuroscientific
evidence and perspectives. In the 1997 article he says that he lacks waking imagery
in all sensory
modes (1997), not just the visual, but, like many other (perhaps all) unimpaired
non-imagers, he does report experiencing vivid dream imagery (including
However, in his 2009 article Faw says that he is "haunted by silent tunes
(with no auditory sound)," which sounds like auditory imagery to me, and
awake I have good non-visual spatial imagery and motor imagery"
(Faw, 2009 p. 46). This seems to contradict his earlier claim that he lacks imagery
in all modes, and it makes me suspicious that Faw's denial of his own imagery
may result from the same sort of conceptual confusions that I (Thomas, 1989)
tentatively suggested might lie behind J.B. Watson's denial of the existence
of imagery. It is interesting, however, that in both his articles
concludes that non-brain damaged, non-impaired non-imagers like himself do have
mental images in the representational sense of the term (see Thomas, 2010 §1.1 for
a discussion of the representational and experiential senses of "imagery"),
that is to say, they he thinks that he does form and make
use of the sorts of quasi-perceptual inner representations that are thought to
be necessary for certain cognitive performances, such as mental rotation, but
for some reason he is unable to bring these imaginal representations to waking
consciousness. Faw (1997)
makes a number of speculative suggestions as to the possible causes of such non-consciousness,
ranging from the neurophysiological to the psychoanalytic, but comes to no definite
conclusion as to which, if any, of them are likely to be correct. His view
seems to be consistent with Marks' suggestion (1986)
that non-imagers suffer from some sort of sub-clinical neurological disconnection
syndrome that somehow makes them unable to report on, or form verbal memories
about, images that they nevertheless, in some sense do experience.
Faw would very much like to see some real empirical research being done on the
*Lucid dreams, are defined as dreams in which the dreamer is aware that he or she is dreaming whilst the dream is in progress. A lucid dreamer may also be able to exercise some conscious, voluntary control over events in the dream.
(vii) There is also a brief account of a very "poor visualizer" in William James' Principles of Psychology, but it is not apparent that this person lacked visual imagery altogether. James quotes him as reporting that:
"The process by which I seem to remember any particular event is not by a series of distinct image, but a sort of panorama, the faintest impressions of which are perceptible through a thick fog. … Everything is vague. I cannot say what I see. … I see nothing in detail. … The coloring is about the same, as far as I can recall it, only very much washed out. Perhaps the only color I can see distinctly is that of the table-cloth, and I could probably see the color of the wall-paper if I could remember what color it was." (James, 1890 ch.18* – the full passage can be read at Google Books)
It would be
interesting to know whether self-professed non-imagers, such as Faw, would accept
this as a description of something similar to their own condition, or whether
they would insist that they do not have even the sort of faint, foggy, vague,
and washed out imagery that James' subject describes here. I invite any non-imagers
who might read this to let me know what they
think about it. (Unfortunately, James goes
on, right after this passage, to repeat Galton's claims, which have now been
shown to be false (Brewer & Schommer-Aikins, 2006), that poor or
non-existent imagery is associated with superior intellect and scientific eminence.)
*The passage is in chapter XVIII (Imagination) of the Principles, on page 57 of volume II of the original 1890 edition, or on pages 703-4 of the single volume 1983 Harvard University Press edition. It can also be found in the chapter on Imagination in James' Psychology: The Briefer Course. In the widely available 1961 edition of the Briefer Course, the one edited and abridged by Gordon Allport (and republished in facsimile by Courier Dover Publications in 2001) the relevant passage is in chapter 10, on page 172. However, Allport's abridgement involved removing the first 9 chapters (which he considered "obsolete"), so presumably it would have been in chapter 19 of the original 1892 version.
Update, April 18 2009: I have now received emails from two seperate non-imagers telling me that the description of the experience of the "poor visualizer" given by James does not fit their experience. They tell me they have no waking visual imagery whatsoever.
(viii) Winch (1908) actually makes the argument, mentioned at the top of this page, that as some cognitively unimpaired people (including himself) do not experience imagery, it can serve little or no cognitive function. Surprisingly, this is the only example of which I am aware of someone actually making this argument in print.
(ix) In his recent book, Eric Schwitzgebel (2011) mentions what may be a very relevant fact told to him by psychologist Russell Hurlburt, with whom he has collaborated. I have been in direct touch with professor Hurlburt, and he confirms what Schwitzgebel says. Hurlburt has developed an interesting technique for studying people's subjective inner experience (see, e.g., Hurlburt, 1990; Hurlburt & Heavey, 2001; Hurlburt & Schwitzgebel, 2007). This involves providing subjects with an electronic beeper that they are asked to carry around with them as they go about their daily business. The beeper is set to go off at occasional, random times, and the subjects have been told that as soon as the beeper goes off, they should jot down in a notebook whatever was going on in their ongoing experience at the moment they heard the beep. (Hurlburt also later interviews the subjects and questions them about what they recall about their inner experience at the times when the beeps went off.) Hurlburt claims that this technique avoids most of the pitfalls and sources of unreliability and bias that have notoriously beset other attempts to study the mind introspectively. Schwitzgebel, it should be said, very much doubts whether this is truly the case (Hurlburt & Schwitzgebel, 2007; Schwitzgebel, 2008), and remains extremely skeptical about the reliability of all types of introspective report, and detailed reports about imagery in particular (Schwitzgebel, 2008, 2002) (although he does not appear seriously to doubt, as Watson did, that imagery experiences really do occur).
Anyway, the point of current relevance is that Hurlburt has told Schwitzgebel (ch. 3, note 1) that he has tried out his beeper technique on several people who claimed, at the outset of the experiment, to be non-imagers. However, when they actually used the beepers, several of them (or perhaps all, it is not entirely clear) did in fact report that they were experiencing visual imagery on some of the occasions when the beepers went off. This suggests that the original claims to be non-imagers were based upon biased or faulty introspection (or retrospection) which the beeper technique was able to correct, and lends support to the contention that all claims to be a non-imager may be due to the unreliabilities inherent in most (or all) introspective reports. That is, despite what some people say, non-imagers may not really exist (or, looking at it another way, perhaps we are all non-imagers if we understand "mental image" the way the professed non-imagers do). However, I must be very tentative about this, because, if Schwitzgebel is right (and I fear he may be), Hurlburt's beeper technique may itself be unreliable. I should also add that Hurlburt told me that the claims to lack imagery were spontaneous remarks made by the subjects in the early stages of briefing them for the experiment. I do not think he recorded their precise words at the time, and he deliberately avoided questioning them about the matter, as he feared that this might contaminate the spontaneity and objectivity their introspective reports later on, whilst wearing the beepers. Thus it is difficult to know precisely what they meant, or how serious they were being, when they claimed not to experience imagery.
brain damage (caused by strokes, head injuries, brain surgery to remove tumors,
etc.) seems to have cause people who previously had normal mental imagery to
lose all or part of their ability to experience it. In most cases, such injuries
also cause severe problems for other aspects of cognition, and particularly visual
perception (for reviews, see Goldenberg, 1989, 1993; Trojano and Grossi, 1994;
Bartolomeo, 2002, 2008).* However, a few rare cases have been reported of brain
damaged patients who seem to have entirely, or almost entirely, lost their ability
to consciously experience visual imagery, but whose perceptual abilities are
less severely affected (Brain, 1954; Basso et al., 1980; Riddoch, 1990; Goldenberg,
1992; Young & van de Wal, 1996; Moro et al., 2008).** Although their
cognitive abilities may be damaged in other ways by their injuries, such patients
do seem to bear some resemblance to the apparently congenital, and cognitively
normal, non-imagers with which this page is concerned.
*It seems to be much more common for brain damage to impair perception but to leave imagery (in the equivalent sense mode) relatively unaffected than for imagery ability to be impaired and perception be largely spared. However, this may be because impairment of imagery is often overlooked when a serious impairment of perception is present. The latter, after all, is usually likely to be much more debilitating to the patient, and much more behaviorally salient to any outside observer.
**Loss of imagery due to neurological disease, coupled with relatively mild perceptual problems, is sometimes referred to as "Charcot-Wilbrand syndrome" after the 19th century French and German neurologists who provided the earliest scientific case studies of it. It has since been realized, however, that Wilbrand's case has been misreported in the subsequent literature, and, in fact, Wilbrand made it clear in his original reports that although his patient was quite badly visually impaired (visual agnosia: she could no longer recognize familiar things and places), and her visual dreaming was much diminished, her ability to experience mental imagery was intact (Solms et al., 1996). Charcot's patient, by contrast, really does appear to have lost his visual imagery (including visual dreams), and the visual agnosia he also suffered, as well as some problems with language and emotion, seems to have been relatively mild (Young & van de Wal, 1996).
A recent case study by Zeman et al. (2010) seems to be more relevant than these others, however, because it describes the case of a man who, although he seems to have almost entirely lost conscious visual imagery due to brain damage (probably from a very mild stroke), is otherwise almost completely unimpaired. (Although Zeman et al. suspect, but have not yet shown that he may have some impairment of "perceptual processes requiring a high degree of top-down control".) Initially, the patient lost visual contents in his dreams too, but these returned after a while. Significantly, however, he claims to have been a strong visual imager (and visual dreamer) beforehand, and (like other patients who have lost imagery via brain damage) he is acutely aware of the difference between his current and former conditions. That would seem to rule out, in this case anyway, the suggestion that I made in my 2001 PSYCHE-D post (above), that the difference between imagers and non-imagers lies more in the way they are inclined to describe their subjective experience than in the experience itself.
The patient apparently noticed his loss of visual imagery about four days after undergoing a coronary angioplasty operation, during which he briefly experienced "reverberation in my head and tingling in my left arm." It seems likely that this was when the damage was actually sustained, even though the loss of imagery did not show up until a few days later. A structural MRI examination of his brain found no abnormalities beyond "minor white matter high intensities and borderline fronto-temporal atrophy, neither clearly falling outside the normal limits for his age" (he was 65) (Zeman et al., 2010).
Detailed testing revealed that, after subjectively losing his imagery, he still performed at essentially normal levels on a variety of cognitive tasks, including some usually thought to involve visual mental imagery. However, his performance did differ from the norm on certain imagery tasks, notably a mental rotation task based on the famous experiment of Shepard & Metzler (1971) and a matrix visualization task originally devised by Brooks (1967), and adapted by Salway & Logie (1995). Although the patient (who appears to have been highly intelligent: IQ 136) was able to complete these tasks with reasonable success, his response patterns were different from those of normal subjects, suggesting that he was using alternative strategies that he had managed to develop instead of the imagery-based strategies thought to be used by most people.
For instance, the Shepard & Metzler rotation task involves presenting subjects with pictures of two similar objects, as seen from different angles, and them asking them to judge whether the objects depicted are the same or are mirror images of one another. Most people say they do the task by visualizing one of the depicted objects and then mentally rotating their image to see if it can be brought into congruence with the object in the other picture. This suggests that their response times (for picture pairs of objects that actually are identical) should be proportional to the angle through which one of the views needs to be rotated to bring it into congruence with the other, and this is indeed what is seen for most subjects. Thus, experimental timing of mental rotation taks has generally been taken as confirming people's introspectively based belief that they accomplish it via imagery. By contrast, although the patient studied by Zeman et al. was able to judge whether the rotated objects were the same or different with reasonable accuracy, his response times did not depend of angle of rotation in the usual, regular way, suggesting that he was not using the imagery based strategy used by most people.
Brain imaging studies, using fMRI, were also conducted on this patient. When he viewed pictures of familiar faces the pattern of activation in his brain was similar to that found in normal subjects. However, when he tried (unsuccessfully) to visualize the same faces, the pattern was different to that seen in successfully visualizing normal subjects. Some of the areas normally activated by face recognition and face visualization – regions of the bilateral fusiform gyri, the superior temporal gyri and sulci, the inferior occipital gyri and the calcarine sulci – were not active when the patient tried to visualize the faces (although they were active, as normal, when he looked at them). Instead, his right anterior cingulate, his bilateral inferior frontal gyri, and his precuneus were more active than those of normal subjects who are successfully visualizing. (Presumably this reflects the unsuccessful efforts at visualization that he is making.)
The extent to which this patient's condition truly resembles that of "regular" non-imagers (i.e., people who do not appear to have suffered any brain injury, but who say they do not experience visual mental imagery), remains unclear. Unfortunately, none of them have ever been studied in the thorough way that he has been. However, superficially, at least, his condition seems to be very like theirs, and he is thus, by far, the best studied case of a non-imager yet.
– Nigel J.T.Thomas
Abelson, R.P. (1979). Imagining the Purpose of Imagery. Behavioral & Brain Sciences (2) 548-549.
Bartolomeo, P. (2002). The Relationship Between Visual perception and Visual Mental Imagery: A Reappraisal of the Neuropsychological Evidence. Cortex (38) 357-378.
Bartolomeo, P. (2008). The Neural Correlates of Visual Mental Imagery: An Ongoing Debate. Cortex (44) 107-108.
Basso, A., Bisiach, E., & Luzzatti, C. (1980). Loss of Mental Imagery: A Case Study. Neuropsychologia (18) 435-442.
Berman, D. & Lyons, W. (2007). The First Modern Battle for Consciousness: J.B. Watson's Rejection of Mental Images. Journal of Consciousness Studies (14 #11) 5-26.
Betts, G.H. (1909). The Distribution and Functions of Mental Imagery. New York: Teachers College, Columbia University.
Brain, R. (1954). Loss of Visualization. Proceedings of the Royal Society of Medicine (47) 288-290.
Brann, E.T.H. (1991). The World of the Imagination: Sum and Substance. Savage, MD: Rowman & Littlefield.
Brewer, W.F. & Schommer-Aikins, M. (2006). Scientists Are Not Deficient in Mental Imagery: Galton Revised. Review of General Psychology (10) 130-146.
Brooks, L.R. (1967). The Suppression of Visualization by Reading. Quarterly Journal of Experimental Psychology (19) 287-299.
Burbridge, D. (1994). Galton’s 100: An Exploration of Francis Galton’s Imagery Studies. British Journal for the History of Science (27) 443-463.
Faw, B. (1997). Outlining a Brain Model of Mental Imaging Abilities. Neuroscience and Biobehavioral Reviews (21) 283-288.
Faw, B. (2009). Conflicting Intuitions May be Based on Differing Abilities: Evidence from Mental Imaging Research. Journal of Consciousness Studies (16 #4) 45-68.
Galton, F. (1880). Statistics of Mental Imagery. Mind (5) 301-318.
Galton, F. (1883). Inquiries into Human Faculty and its Development. London: Macmillan.
Goldenberg, G. (1989). The Ability of Patients with Brain Damage to Generate Mental Visual Images. Brain (112) 305-325.
Goldenberg, G. (1992). Loss of Visual Imagery and Loss of Visual Knowledge - A Case Study. Neuropsychologia (30) 1081-1099.
Goldenberg, G. (1993). The Neural Basis of Mental Imagery. Baillière's Clinical Neurology (2) 265-286.
Hurlburt, R.T. (1990). Sampling Normal and Schizophrenic Inner Experience. New York: Plenum Press.
Hurlburt, R.T. & Heavey, C.L. (2001). Telling What We Know: Describing Inner Experience. Trends in Cognitive Sciences (5 #9) 400-403.
Hurlburt, R.T. & Schwitzgebel, E. (2007). Describing Inner Experience?: Proponent Meets Skeptic. Cambridge, MA: MIT Press.
James,W. (1890). Principles of Psychology. New York: Holt.
James, W. (1892). Psychology: The Briefer Course New York: Holt. (1961 edition, edited and abridged by G. Allport: New York: Harper Torchbooks.)
Kosslyn, S.M. (1980). Image and Mind. Cambridge, MA: Harvard University Press.
Kosslyn, S.M. (1983). Ghosts in the Mind's Machine: Creating and Using Images in the Brain. New York: Norton.
Kosslyn, S.M. (2002). What Shape Are a German Shepherd's Ears? Interview transcript, online at http://www.edge.org/3rd_culture/kosslyn/kosslyn_print.html [Retrieved January 31st, 2012].
Marks, D.F. (1986). The Neuropsychology of Imagery. In D.F. Marks (ed.). Theories of Image Formation (pp. 225-241). New York: Brandon House.
Moro, V., Berlucchi, G., Lerch, J., Tomaiuolo, F., & Aglioti, S.M. (2008). Selective Deficit of Mental Visual Imagery with Intact Primary Visual Cortex and Visual Perception. Cortex (44) 109-118.
Richardson, A. (1969). Mental Imagery. New York: Springer.
Riddoch, M.J. (1990). Loss of Visual Imagery: A Generation Deficit. Cognitive Neuropsychology (7) 249-273.
Salway, A.F., & Logie, R.H. (1995). Visuospatial Working Memory, Movement Control and Executive Demands. British Journal of Psychology (86) 253-269.
Schwitzgebel E. (2002). How Well Do We Know Our Own Conscious Experience? The Case of Imagery. Journal of Consciousness Studies (9) 35-53.
Schwitzgebel, E. (2008). The Unreliability of Naive Introspection. Philosophical Review (117 #2) 245-273.
Schwitzgebel, E. (2011). Perplexities of Consciousness. Cambridge, MA: MIT Press. [Draft versions of each chapter are currently available at Eric Schwitzgebel's web site.]
Shepard, R.N. & Metzler, J. (1971). Mental Rotation of Three-Dimensional Objects. Science (171) 701-703.
Solms, M., Kaplan-Solms, K., & Brown, J.W. (1996). Wilbrand's Case of "Mind Blindness". In Code, C.,Wallesch, C.-W., Joanette, Y., & Lecours, A.R (Eds.) Classic Cases in Neuropsychology (pp. 89-110). Hove, UK: Psychology Press.
Sommer, R. (1978). The Mind's Eye. New York: Delacorte Press.
Thomas, N.J.T. (1989). Experience and Theory as Determinants of Attitudes toward Mental Representation: The Case of Knight Dunlap and the Vanishing Images of J.B. Watson. American Journal of Psychology (102) 395-412.
Thomas, N.J.T. (2010). Mental Imagery. In E.N. Zalta (ed.), The Stanford Encyclopedia of Philosophy. Stanford, CA: CSLI (Online, Open Access publication).
Trojano, L. & Grossi, D. (1994) A Critical Review of Mental Imagery Defects. Brain and Cognition (24) 213-243.
Winch, W.H. (1908). The Function of Images. Journal of Philosophy, Psychology and Scientific Methods (5 #13) 337-352.
Young, A. & van de Wal, C. (1996). Charcot's Case of Impaired Imagery. In Code, C.,Wallesch, C.-W., Joanette, Y., & Lecours, A.R (Eds.) Classic Cases in Neuropsychology (pp. 31-44). Hove, UK: Psychology Press.
Zeman, A.Z.J., Della Sala, S., Torrens, L.A., Gountouna, V.-E., McGonigle, D.J., & Logie, R.H. (2010). Loss of Imagery Phenomenology with Intact Visuo-spatial Task Performance: a Case of 'Blind Imagination.' Neuropsychologia (48 #1) 145-155.
Return to Home Page:
Imagination, Mental Imagery, Consciousness, Cognition:
Science, Philosophy & History.