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The Rediscovery of the Unconscious


John F. Kihlstrom

University of California, Berkeley


Versions of this paper were presented as the presented at the Inaugural Symposium of the Krasnow Institute for Advanced Study, George Mason University, sponsored by the Krasnow Institute and the Santa Fe Institute, Fairfax, Virginia (May, 1993); the F.J. McGuigan Lecture on Understanding the Human Mind, sponsored by the American Psychological Foundation, presented at the annual meeting of the American Psychological Association, Boston (august 1999);  the keynote address presented at the annual meeting of the Australian Psychological Society, Hobart, Tasmania (September 1999); and at the Vienna Conference on Consciousness held at the University of Vienna (October 2007).  

Shorter versions of this paper were published in H. Morowitz & J. Singer & (Eds.), The Mind, the Brain, and Complex Adaptive Systems (pp. 123-143). Santa Fe Institute Studies in the Sciences of Complexity, Vol. 22. Reading, Ma.: Addison-Wesley.  An updated, edited version will appear as Chapter 1 of The Unconscious Mind, currently in preparation for MIT Press.


In the last quarter of the 19th century, as the new science of psychology began to emerge from its roots in philosophy and physiology, consciousness was at the center of the enterprise. The early psychophysicists, such as Ernst Weber (1795-1878) and Gustav Fechner (1801-1887) were concerned with the relations between the objective, physical properties of environmental stimuli and the subjective, psychological properties of the conscious mental states to which they gave rise. A major goal of 19th-century psychophysics was to determine the absolute and relative thresholds for conscious experience. These were, respectively, the minimum intensity required for an observer to become aware of the presence of a stimulus, and the minimum increase or decrease in intensity required for an observer to be aware that the stimulus had changed. The methods of psychophysics, such as the "just-noticeable difference", the method of constant stimuli, and the method of adjustment, were the first attempts to quantify subjective experience.1 The psychophysical laws, which sought to relate every psychological property of a sensation to some physical property of the corresponding experience, were the first attempt to determine the physical basis of consciousness.2

Beginning with Wilhelm Wundt (1832-1920) and his American protégé E.B. Titchener (1867-1927), the school of psychology known as structuralism attempted a kind of "mental chemistry" which sought to analyze conscious experience into its constituent sensations, images, and feelings (Titchener, 1898). The structuralists' preferred method of investigation, called introspection, assumed that people had accurate conscious awareness of their own mental states (E.G. Boring, 1953). The structuralists had a particular perspective on psychophysics. In contrast to physics, which they defined as the study of the facts of experience independent of the observer, psychology was defined as the study of these same facts as dependent on the experiencing individual (Titchener, 1929/1972). In this way the very first school was, first and foremost, devoted to the study of conscious experience.

Nevertheless, structuralism was hounded by a number of difficulties (E. G. Boring, 1950; Hilgard, 1987). For example, a protracted debate between Titchener and Oswald Kulpe (1862-1917), over whether one could have thoughts without images, revealed that introspection was not always a reliable method. Nevertheless, we owe to the structuralists the discovery of the basic dimensions of certain sensory and emotional experiences. For example, although Sir Isaac Newton (1642-1727) discovered that a prism refracts light into seven primary colors, from a psychological point of view there are only four: red, yellow, green, and blue. This kind of work, in turn, laid the basis for the later search for the neural correlates of what philosophers call sensory qualia. For example, we now know that the physiological basis for color vision is a set of four neural systems, arranged as opponents: red-yellow, and green-blue (DeValois, 1965; Hering, 1878/1964; Hurvich & Jameson, 1957). Without the structuralists' analyses of conscious experience, neuroscientists might well have searched long and in vain for seven neural systems corresponding to the physical primaries.3 The achievements of structuralism were summarized by E.G. Boring (1933) with a monograph appropriately entitled The Physical Dimensions of Consciousness.

Even William James, opposed as he was to the doctrines of structuralism (Hilgard, 1987), embraced a version of introspection as his preferred research method (he had a collection of brass instruments, but he hated using them). James worried a great deal about the liabilities of introspection, and sought to supplement the technique with experimental methods. James began his Principles of Psychology with the assertion that "Psychology is the science of mental life" (James, 1890/1980, p. 1). By this he meant conscious mental life -- as James made abundantly clear in the Briefer Course (1892/1980, p. 1), where he adopted G.T. Ladd's (1887) definition of psychology as "the description and explanation of states of consciousness as such". For James, as for Descartes, consciousness came first, even before sensation: "The first fact for us then, as psychologists, is that thinking of some sort goes on" (James, 1890/1980, p. xxx).


The Unconscious Before Freud

At the same time, both James and the structuralists understood that there was more to mental life than was accessible to introspection. The notion that unconscious processes are important elements of mental life is commonly ascribed to Sigmund Freud, the founder of psychoanalysis, but in fact it was an old idea before Freud was even born (Ellenberger, 1970; D. B. Klein, 1977; Whyte, 1960).4


The Threshold of Consciousness

At the beginning of the 18th century, the German philosopher Gottfried Wilhelm Leibniz (1646-1716) had written that our conscious thoughts are influenced by petites perceptions -- sensory stimuli of which we are not aware:

...at every moment there is in us an infinity of perceptions, unaccompanied by awareness or reflection.... That is why we are never indifferent, even when we appear to be most so.... The choice that we make arises from these insensible stimuli, which... make us find one direction of movement more comfortable than the other (Leibniz, 1704/1981, p. 53).

Because he believed that perception could be unconscious, Leibniz introduced the term apperception to refer to conscious perception.

At the close of that century, Immanuel Kant (1724-1804) devoted a major section of his last work, Anthropology from a Pragmatic Point of View,5 to a discussion "Of the ideas which we have without being conscious of them":

To have ideas, and yet not be conscious of them, -- there seems to be a contradiction in that; for how can we know that we have them, if we are not conscious of them? Nevertheless, we may become aware indirectly that we have an idea, although we be not directly cognizant of the same (Kant, 1798/1978, p. 18).

Kant also accepted Leibniz’s distinction between unconscious perception and conscious apperception, and further distinguished between the "epmirical apperception" of conscious awareness and the "transcendental unity of apperception", or the interconnectedness of all conscious thought.

In the 19th century, Johann Friedrich Herbart (1776-1841), drawing on the views of Leibniz, defined the limen, or sensory threshold, as a mental battleground where various perceptions, themselves mostly unconscious, competed for representation in consciousness:

One of the older ideas can… be completely driven out of consciousness by a new much weaker idea. On the other hand its pressure there is not to be regarded as without effect; rather it works with full power against the ideas which are present in consciousness. It thus causes a particular state of consciousness, though its object is in no sense really imagined (Herbart, 1816/1881, p. 19).

Herbart's concept of thresholds set the agenda for 19th-century psychophysics, and his ideas continue to reverberate in the controversy over subliminal perception (R.F> Bornstein & Pittman, 1992; Dixon, 1971, 1981)). In addition, Herbart’s notion that one idea can prevent another from attaining consciousness lies at the foundation of Freud’s psychoanalytic theory of repression and defense (Ellenberger, 1970).


Unconscious Inference

Among the most influential advocates of unconscious mental processes was the German physiologist Hermann von Helmholtz (1821-1894). In his Treatise on Physiological Optics, he argued that our conscious perceptions are determined by unconscious inferences concerning the stimulus environment:

The psychic activities that lead us to infer that there in front of us at a certain place there is a certain object of a certain character, are generally not conscious activities, but unconscious ones. In their result they are the equivalent to conclusion, to the extent that the observed action on our senses enables us to form an idea as to the possible cause of this action.... But what seems to differentiate them from a conclusion, in the ordinary sense of that word, is that a conclusion is an act of conscious thought.... Still it may be permissible to speak of the psychic acts of ordinary perception as unconscious conclusions... (Helmholtz, 1866/1968, p. 174; Warren & Warren, 1968).

For Helmholtz, then, perception results from a kind of syllogistic reasoning, in which the major premise consists of knowledge about the world acquired through experience, and the minor premise consists of the information provided by the proximal stimulus. The perception of this proximal stimulus, then, is the conclusion of the syllogism -- except, in the case of perception, we are not aware of the reasoning process. Hence, Helmholtz’s phrase, "unconscious conclusions".6 The fact that the reasoning underlying perception is unconscious is what makes us feel that we are seeing the world the way it really is. But our percepts are not immediate products of stimulation -- they are mediated by unconscious reasoning processes.

Slide1.JPG (14989 bytes)The phenomenon of size constancy, depicted in Figure 1,7 illustrates Helmholtz's unconscious inferences in operation. Every object in our visual field casts an image of itself on the retinas of our eyes. As a matter of optical physics, the size of the retinal image is proportional to the size of the object, but inversely proportional to the distance between the object and the observer. Thus, objects A and B, which differ in both size and distance from the observer, cast images of the same size on the observer’s retina. When an object moves closer to us, the size of its retinal image grows, as from A to A’, but we do not perceive the object as growing in size. This is size constancy. In order to maintain size constancy, the visual system takes account of cues to distance, and essentially multiplies retinal size by distance.8 In Helmholtz’ terms, given the knowledge about the size of the distal stimulus as a major premise, and the minor premise that the proximal stimulus cast on the retina is growing in size, perceivers apply the size-distance rule and conclude that the object is coming nearer. We are not aware of making these calculations, of course, and we don't draw the logical conclusion consciously and deliberately. It all just happens automatically, based on knowledge acquired through experience, as part of the proper functioning of the visual system.

Helmholtz’ theory of unconscious inference had roots in the earliest accounts of optics and vision, beginning with the Greco-Egyptian astronomer Ptolemy and the Arab mathematician Ibn al-Haytham and running through Descartes, Kant, and Berkeley (for a critical review, see Hatfield, 2002). Nevertheless, both James (1890/1980) and Klein (1977) asserted that Helmholtz later repudiated the notion of unconscious inferences. In fact, his later writings make clear that Helmholtz had reservations only about the term, not the idea.

"Later I avoided that term, 'unconscious conclusions', in order to escape from the entirely confused and unjustified concept -- at any rate so it seems to me -- which Schopenhauer and his disciples designate by this name" (Helmholtz, 1878/1968, p. 220).

Helmholtz reaffirmed the basic idea of unconscious inferences in one of his last essays, republished as part of the second edition (1896) of the Treatise on Physiological Optics:

"…I find even now that this name is admissible within certain limits since these associations of perceptions in the memory actually take place in such a manner, that at the time of their origin one is not aware of it… (Helmholtz, 1894/1968, p. 255).

Despite challenges (e.g., Gibson, 1966; Gibson, 1979), Helmholtz’ theory of unconscious inference continues to dominate theoretical discussion of perceptual processes (Hatfield, 2002). Unconscious inference lies at the core of the "constructivist" view of perception, which holds that the pattern of proximal stimulation is not sufficient to yield perception. Rather, perception is an intelligent activity by which the perceiver constructs an internal, mental representation of the world by combining information provided by the stimulus environment with world-knowledge retrieved from memory (e.g., Gregory, 1966, 1970; Hochberg, 1964, 1978; Irvin Rock, 1983, 1995, 1997). Rock, in particular, argued that perception that unconscious (or, at least, unnoticed) cognitive processes occur at four different stages in the perceptual process: form perception, the resolution of stimulus ambiguity, the perception of the relations among the objects of perception, and the construction of perceptual constancies.


Romantic Views of the Unconscious

The pre-Freudian analysis of unconscious mental life reached its apex with Eduard von Hartmann (1842-1906) and his Philosophy of the Unconscious (1868/1931), an extremely popular work whose three volumes, running to more than a thousand pages, went through a total of 12 editions (the last published in 1923). For Hartmann, the universe was ruled by the Unconscious (the initial capital is his) a highly intelligent dynamic force composed of three layers: the Absolute Unconscious, accounting for the mechanics of the physical universe; the Physiological Unconscious, underlying the origin, evolution, development, and mechanisms of life; and the Relative Unconscious, which Hartmann considered to be the origin of conscious mental life. Hartmann's "relative unconscious" is what I prefer to call the psychological unconscious -- a term referring to those mental states and processes which influence our experience, thought, and action outside phenomenal awareness and independent of voluntary control.

Hartmann ascribed a number of specific functions to the Unconscious (Vol. 2, pp. 38-39):

1. The Unconscious forms and preserves the organism, repairs its inner and outer injuries, appropriately guides its movements, and mediates its employment by the conscious will.

2. The Unconscious supplies every being in its instinct with what it needs for self-preservation, and for which its conscious thought does not suffice….

3. The Unconscious preserves the species through sexual and maternal love… and conducts the human race historically steadily to the goal of its greatest possible perfection.

4. The Unconscious often guides men in their actions by hints and feelings, where they could not help themselves by conscious thought.

5. The Unconscious furthers the conscious process of thought by its inspirations…, and in mysticism guides mankind to the presentiment of higher, supersensible unities.

6. It makes men happy through the feeling for the beautiful and artistic production.

We owe to Hartmann the notion, still with us in some quarters today, that the unconscious possesses capacities and powers that are superior to those available to ordinary consciousness:

If we now institute a comparison between the Conscious and Unconscious, it is first of all obvious that there is a sphere which is always reserved to the Unconscious, because it remains forever inaccessible to consciousness. Secondly, we find a sphere which in certain beings only belongs to the Unconscious, but in others is also accessible to consciousness. Both the scale of organisms as well as the course of the world's history may teach us that all progress consists in magnifying and deepening the sphere open to consciousness; that therefore in a certain sense consciousness must be the higher of the two. Furthermore, if in man we consider the sphere belonging both to the Unconscious and also to consciousness, this much is certain, that everything which any consciousness has the power to accomplish can be executed equally well by the Unconscious, and that too always far more strikingly, and therewith far more quickly and more conveniently for the individual, since the conscious performance must be striven for, whereas the Unconscious comes of itself and without effort…. [T]he Unconscious can really outdo all the performances of conscious reason…" (Vol. 2, pp. 39-40).

Hartmann’s view of the unconscious is in tune with the romanticism that characterized much European and American literature, art, and music in the 19th century (Whyte, 1960). As a rebellion against both classicism and rationalism, romanticism celebrated nature, sensuality, and feelings -- including what Whyte (p. 132) called "the dark realms of the soul". Jean-Jacques Rousseau (1712-1778) celebrated the unconscious and involuntary role of the will and emotions in behavior; Johann Gottlieb Fichte (1762-1814) asserted that unconscious impulses reflected the intelligence of nature; Friedrich William Joseph von Schelling (1775-1884) asserted that a single unconscious principle organized all of nature; Johann Wolfgang von Goethe (1749-1832), the poet who epitomized the sturm und drang school of German literature, celebrated the unconscious roots of human invention and discovery, and asserted that the roots of human nature were in the Unconscious. Arthur Schopenhauer, (1788-1860), the philosopher whose writings caused Helmholtz to regret using the word "unconscious", asserted that our experience of nature was governed by a unconscious and impersonal Will, which is the source of all human pain and suffering, and from which humans must become detached to survive. Hartmann’s Philosophy of the Unconscious comes straight out of Schopenhauer, and leads straight into Friedrich Wilhelm Nietzsche (1844-1900), who wrote that consciousness is only the last, and the weakest, stage in organic evolution. And we know what came from Nietzche: no wonder Helmholtz was worried!

However influential Romanticism was on 19th-century European intellectual life, in the end Hartmann's ideas proved to be too speculative for the first generation of scientific psychologists. Herman Ebbinghaus, discussing Hartmann's book, concluded that "Wherever the structure is touched, it falls apart…. What is true is not new, and what is new is not true" (Shakow, 1930, p. 510)). William James echoed the criticism:

Hartmann fairly boxes the compass of the universe with the principle of unconscious thought. For him there is no namable thing that does not exemplify it. But his logic is so lax and his failure to consider the most obvious alternative so complete that it wold, on the whole, be a waste of time to look at his arguments in detail (James, 1890/1980, p. 171).


Freud and Psychoanalysis

Despite James’s reaction, all of this activity, from Leibniz and Kant to Helmholtz and Hartmann, and beyond, laid the foundation for what Henri Ellenberger , the great historian of psychiatry, called The Discovery of the Unconscious (Ellenberger, 1970). As early as 1868 -- the very year that Hartmann published his Philosophy of the Unconscious -- Henry Maudsley, the father of British psychiatry (after whom the Maudsley Psychiatric Institute in London is named) had noted that "we cannot overestimate the importance of the fact that 'consciousness' is not coextensive with the mind" (Maudsley, 1876/1977, p. xxx). The psychiatric discovery of the unconscious was consolidated with what Ellenberger called a new dynamic psychiatry B the psychiatry of Freud, Jung, and Adler. According to Ellenberger, Leibniz had coined the term "dynamic" to make the point that mental states were active rather than static, and this usage persisted in the hands of Herbart and Fechner. What unites all the dynamic approaches to mental illness is the idea that unconscious mental contents, far from being latent (like unattended stimuli and forgotten memories), actively influence the person's conscious experience, thoughts, and actions. Dynamic psychiatry is based on motives -- not just ideas, but ideas with force behind them; these motives, in turn, are unconscious, so that we do not know why we do what we do.

Based on their clinical observations, for example, Breuer and Freud (1893-1895/1953) concluded that the symptoms of hysteria were produced by unconscious memories of traumatic events (Breuer & Freud, 1893-1895/1953). As they famously put it, "hysterics suffer mainly from reminiscences" (pp. 7).

Our observations have shown... that the memories which have become the determinants of hysterical phenomena persist for a long time with astonishing freshness and with the whole of their affective colouring. We must, however, mention another remarkable fact... that these memories, unlike other memories of their past lives, are not at the patients' disposal. On the contrary, these experiences are completely absent from the patients' memory when they are in a normal psychical state, or are only present in highly summary form. Not until they have been questioned under hypnosis do these memories emerge with the undiminished vividness of a recent event (p. 9).

Freud, of course, went on to elaborate a theory which attributed all conscious experiences, thoughts, and actions to unconscious sexual and aggressive drives, and defense mechanisms (such as repression) unconsciously deployed to control them. When James and Freud met at the famous Clark University conference of 1909, James reportedly told Ernest Jones, a young disciple of Freud and later Freud's biographer, that "the future of psychology belongs to your work".9 We do not know exactly what James meant by this remark (Taylor, 1999), or even whether he actually said it. We can suppose that he referred to the analysis of unconscious mental life. In any event, we do know that, for better or for worse, Freud's theories dominated both scientific and popular conceptions of the unconscious for most of the next century.


Consciousness and the Unconscious After Watson

Unfortunately, just when the concept of the psychological unconscious was getting up steam, the behaviorist revolution hit. Interest in consciousness disappeared virtually overnight, and interest in the psychological unconscious went with it. For John B. Watson (1878-1958), the founder of behaviorism, and his comrades in arms, the only way to make psychology truly scientific was to abandon the mental, and focus on behavior. Watson did not deny the existence of consciousness: he only denied that consciousness was subject to scientific investigation. It was bad enough to try to explain behavior in terms of mental states that couldn't be publicly observed; it was even worse to try to explain behavior in terms of mental states that couldn't be privately observed! For Watson, the job of psychology was to discover laws relating publicly observable environmental stimuli with publicly observable muscular and glandular responses (Watson, 1913, 1919). Behavior was construed as a string of innate and conditioned reflexes. Introspection was replaced with verbal reports, though verbal reports, as pieces of behavior, were admitted into the science only when they could be compared with objective stimulus conditions. "The unconscious" was reformulated by Watson merely as the unverbalized (Watson, 1928, pp. 93-115).

Of course, psychological interest in consciousness did not die completely with the triumph of behaviorism. Some psychologists influenced by psychoanalysis maintained an interest in consciousness, as well as the unconscious. Of particular importance here was the movement known as psychoanalytic ego psychology. While Sigmund Freud was primarily interested in the id -- the primitive, irrational, biological drives that he felt were the dynamic core of personality, some of his followers, including his daughter Anna (Freud, 1936/1937), took an interest in the ego, and especially the "conflict-free sphere" of the ego, which enabled the person to form mental representations of external reality (e.g., Hartmann, 1939; Rapaport, 1959). At a time when academic psychology was still dominated by the functional behaviorism of Watson and Skinner, the sensory psychophysics of Stevens, and stimulus-response theories of animal and verbal learning, psychoanalytic ego-psychologists were publishing investigations of cognitive development in infants and children, memory for connected discourse, atttributions of causality, individual differences in cognitive style, mental imagery, and preconscious processing. Much like the monks of the Middle Ages, the ego psychologists held fast against the behaviorist onslaught, preserving what was most interesting in psychology until psychologists were ready to study the mind again.

There were others besides psychologists who prefigured the cognitive revolution and the resurgence of interest in consciousness. The entire Gestalt movement in perception was fundamentally concerned with the nature of conscious experience. (I. Rock & Palmer, 1990). McDougall's hormic psychology argued against Watson that behavior has a purpose, and is not just a response to stimulation; for MacDougal, each episode of mental life began with a thought, continued with an intention, and ended with a feeling (McDougall, 1923). Woodworth's (1938) work on the span of apprehension is essentially an investigation of the limits of consciousness, and presaged work on attention that heralded the cognitive revolution (Woodworth, 1938). Even earlier, Wallas's analysis of thinking had contrasted an unconscious stage of incubation with the conscious stages of preparation, illumination, and verification (Wallas, 1921). Still, a full-scale revival of academic interest in consciousness had to wait until behaviorism was overthrown by the cognitive revolution. And when the cognitive revolution happened, consciousness was there in the thick of it

In the 1950s and 1960s, research on selective attention (Broadbent, 1958), primary or short-term memory (Atkinson & Shiffrin, 1968; Waugh & Norman, 1965), and especially on mental imagery (Richardson, 1969; Segal, 1971; Sheehan, 1972) legitimized the study of consciousness.10 Somewhat ironically, however, the early cognitive psychologists hardly ever used the term consciousness itself. This is a result, I think, of four tendencies described by the philosopher Owen Flanagan (1992).

First, as a methodological holdover from behaviorism, is a positivistic reserve reflecting our persisting reluctance to use mentalistic language. Behavior is our window on the mind, but many psychologists remain more comfortable talking about behavior than about mental states.

Second, cognitive psychology prefers a piecemeal approach that assumes that big problems like consciousness can be solved by working up from the bottom on smaller problems like attention and short-term memory. At a cocktail party, one of the world's leading cognitive psychologists once told me proudly that he had written a dozen books without ever using the word consciousness. A focus on discrete phenomena, without addressing the big picture, essentially marginalizes the subject of consciousness. Compare, in undergraduate psychology curricula, the number of courses on consciousness to the number of courses on perception, memory, intelligence and problem-solving, or judgment and decision-making.

The study of consciousness can survive piecemeal approach by investigators suffering hangovers of positivistic reserve, but two more trends described by Flanagan are more dangerous.

One is the epiphenomenalist suspicion: the idea that consciousness is the endproduct of cognitive functioning, but plays no causal role in human experience, thought, and action. From this point of view, we are conscious automata -- zombies who know what we're doing, perhaps, but zombies nonetheless.

From this stance it is only a short step to conscious inessentialism -- the view that understanding consciousness is simply not important to understanding how the human mind works. Within cognitive psychology (and cognitive science generally), proponents of "computational functionalism" seek to describe human cognition in terms of the functional relations between stimuli and responses. This may sound like a throwback to Watsonian and Skinnerian behaviorism, and in some respects it is -- the principal difference being that the computational functionalists are interested in the information-processing structures that mediated between stimulus and response, while Watson and Skinner were not. But computers process information, and hardly anyone raises the question of whether they are conscious. Accordingly, it may seem to some that we might have a complete description of human information processing without ever getting to the topic of consciousness at all.

If the cognitive revolution laid the basis for the revival of interest in conscious mental life, the attitudes just described sowed the seeds for a revival of interest in unconscious mental life as well. There were other sources as well. At the very beginning of the cognitive revolution, the linguist Noam Chomsky (1957) argued that human language was mediated by "deep" grammatical structures which are inaccessible to conscious introspection, and can be known only by inference (see, especially, Chomsky, 1980)). Along the same lines, the philosopher Jerry Fodor argued that many mental functions, such as visual perception, were mediated by dedicated structures which were impenetrable by conscious awareness and control (Fodor, 1983). As noted earlier, cognitive approaches to perception, as exemplified by the work of Irvin Rock on visual illusions, invoked a version of Helmholtz's notion of unconscious inference to explain both how we see the world the way we do (Irvin Rock, 1983, 1997). Finally, the classic multistore model of memory, which made a place for consciousness in attention and primary memory, made a place for the psychological unconscious in its list of preattentive, or preconscious, information processing functions (Atkinson & Shiffrin, 1968; Waugh & Norman, 1965).


Four Roads to the Unconscious

In the final analysis, however, the revival of interest in the psychological unconscious was not just a byproduct of psychologists' squeamishness about consciousness and mentalistic talk, and it was more than an expansion of footnotes in theories of perception or thinking. Interest in the psychological unconscious now runs wide and deep within psychology. This happy state of affairs is the end product of at least four quite independent strands of investigation, which together converge on our modern conception of unconscious mental life.



Slide2.JPG (16769 bytes)One research tradition contributing to the modern interest in the psychological unconscious is based on a distinction between "automatic" and "strategic" mental processes. Skilled reading provides one example of automaticity: we recognize certain patterns of marks on the printed page as letters, and certain patterns of letters as words, and decode the meanings of words in light of the words around them, but we rarely have any conscious awareness of the rules by which we do so. It just happens, as an automatic consequence of having learned to read. The power of these processes is illustrated by the color-word effect discovered by Stroop (MacLeod, 1991; see also MacLeod, 1992; 1935), illustrated in Figure 211 In the basic "Stroop" experiment, subjects are presented with a list of color names printed in different colors, and are asked to name the color in which each word is printed. This task is easy if the ink-color matches the color name (e.g., the word yellow printed in yellow ink); but if the word and its color do not match (e.g., yellow printed in green ink), it is very hard. Despite the subjects' conscious intention to name ink colors, and to ignore the words themselves, they cannot help reading the color names, and this interferes with naming of the colors. It just happens automatically.

According to traditional formulations (e.g., Schneider & Shiffrin, 1977), automatic processes are inevitably engaged by the appearance of specific environmental stimuli, independent of the person's conscious intentions. Once invoked, they proceed incorrigibly to their conclusion. In theory, their execution consumes no attentional resources, and for this reason (and perhaps also because they are executed very rapidly) they leave no traces of themselves available to conscious recollection. Hasher and Zacks (1979) have further suggested that automatic processes do not improve with training or feedback. Furthermore, assuming that the person is neurologically intact, once they have been acquired automatic processes are invariant across age, education, socioeconomic status, race, and ethnicity.

The unconscious inferences discussed by Helmholtz (1866/1968) probably occur automatically. Certainly we are not aware of making these inferences, and we do not intend to make them -- they just seem to happen in the course of perceiving, and we are consciously aware only of their endproduct. In theory, some mental processes are innately automatic, while other processes become automatized only after extensive practice with a task. More recently, some hypothesized properties of automaticity have been called into question by revisionist, memory-based theorists (e.g., Logan, 1997). But even these revisionist views agree that some mental processes are unconscious in the strict sense of the term: they are inaccessible to phenomenal awareness under any circumstances, and can be known only by inference from task performance.



Both traditional and revisionist approaches to automaticity assume, at least tacitly, that the mental contents upon which these processes operate are accessible to conscious awareness. However, it is now clear that our experiences, thoughts, and actions can be influenced by mental contents B percepts, memories, thoughts, feelings, and desires, of which we are unaware. Compelling evidence for this proposition began to accumulate in the 1960s, as cognitive psychology turned into cognitive neuropsychology, and researchers began to see evidence of the psychological unconscious in the behavior of brain-damaged patients.

Pride of place in this history goes to studies of the amnesic syndrome, sometimes known as "Korsakoff’s syndrome" after the neurologist who first described it, which results from bilateral damage to the hippocampus and related structures in the medial temporal lobe, or, alternatively, to the mammillary bodies and related structures of the diencephalon, which includes the thalamus and hypothalamus (S. S. Korsakoff, 1889a/1996; S.S. Korsakoff, 1889b/1955; Talland, 1965). On clinical observation, such patients show a dense anterograde amnesia for "postmorbid" events that occurred after the brain damage: after only a few moments of distraction, they cannot consciously remember events that have occurred just recently. They may also show some degree of retrograde amnesia, covering "premorbid" events that occurred prior to the brain damage, but this point is controversial and need not concern us here. As the study of these patients shifted from clinical description to controlled laboratory investigation, however, it became apparent that the events apparently covered by the amnesia nonetheless influenced the patients' ongoing experience, thought, and action.

Slide3.JPG (30252 bytes)For example, Warrington and Weiskrantz (1970, Experiment 2) asked amnesic patients to study a list of words. Figure 312 shows the results of several memory tests conducted a short while later. Compared to nonamnesic controls, the amnesic patients showed profound deficits on standard tests of recall or recognition: this is the basic phenomenon of anterograde amnesia. Then they were provided with the first three letters of previously studied items, and asked to complete the word "stem" with an English word. Both amnesics and controls performed extremely well on this "partial information" test -- a phenomenon known as repetition priming because the cue provided at the time of testing is a recapitulation (at least in part) of an item presented during the study phase.

Repetition priming is clearly an effect of memory: if some trace of studied items did not remain, there would be way for the subject to guess the word represented by stem. Interestingly, the amnesic patients had little or no conscious recollection of the study phase, and treated the partial information test as a kind of guessing game. "Guessing" proved to be an important element in their performance. Later research showed that when amnesic patients were specifically instructed to complete word stems and fragments with items from the studied list, they did not perform as well as controls (e.g., Graf, Squire, & Mandler, 1984). Nevertheless, the fact that they displayed levels of repetition priming equivalent to those of controls -- indeed, the fact that they displayed significant levels of priming at all -- showed that, in some sense, they still retained some memories of their previous experience.

Based on obervations of spared priming and similar effects, Schacter (1987)(1987) and other theorists have drawn a distinction between two expressions of memory, explicit and implicit. Explicit memory refers to one's conscious recollection of the past, as manifested on tasks like recall and recognition. Implicit memory, by contrast, refers to any change in experience, thought, or action that is attributable to a past event, regardless of whether that event is consciously remembered. Repetition priming effects, in which prior exposure to a word like table makes it more for a person to complete the stem tab__ with table than with tablet or taboo, or prior exposure to a word like assassin makes it easier for a person to complete a fragment like __ss___ss__ at all, are good examples of implicit memory. They obviously depend on memory, but the task does not refer to the past, nor, logically, does it require conscious recollection of any past event. All the subject has to do is to generate an acceptable word that fits in the spaces provided. The sparing of implicit memory in amnesia shows that some representation of a prior event has been encoded and stored in memory, and influences ongoing experience, thought and action, even though that event cannot be consciously remembered. Implicit memories are unconscious memories.

Research on neuropsychological patients also revealed unconscious influences in the perceptual domain. Perhaps the most dramatic example is the phenomenon of blindsight documented in some patients with damage to the striate cortex of the occipital lobe (Weiskrantz, 1986). Such patients experience a scotoma B a portion of the visual field where they have no visual experience. When a visual stimulus is presented to that portion of the visual field corresponding to their scotoma, they see nothing at all. Yet their conjectures about the visual properties of the stimulus can be amazingly accurate. For example, the patient known as R.B., studied by Weiskrantz, made guesses about the presence, location, form, movement, velocity, orientation, and size of objects that were more accurate than would be expected by chance alone. The latest evidence suggests that blindsight patients can even make rather difficult discriminations among facial expressions of emotions, even though they cannot consciously see the faces in question (DeGelder, Vroomen, Pourtois, & Weiskrantz, 1999). Just as amnesic patients are influenced by past events that they cannot consciously remember, so blindsight patients can respond to visual stimuli in their current environments that they cannot consciously perceive.

redis23.gif (4881 bytes)Something similar occurs in at least some cases of visual neglect arising from lesions in the temporo-parietal region of one hemisphere (usually the right) that do not affect primary sensory or motor cortices.


Subliminal Perception

Perception without awareness can also be observed in neurologically intact subjects, in the form of "subliminal" perception. In the 19th century, Herbart's proposal that there is a limen, or threshold, which must be crossed before a stimulus could be consciously perceptible stimulated the development of psychophysicists. However, Leibniz's notion of petites perceptions implied that there were percepts below the limen. If these percepts actively influenced behavior, as Leibniz argued, then perhaps there was no limen at all. The quest to document subliminal perception began in the 1880s (Peirce & Jastrow, 1884), resulting in the accumulation of a substantial body of positive evidence (Adams, 1957; Dixon, 1971).

Unfortunately, these experiments were subject to vigorous and often persuasive criticism, mostly on methodological grounds (Eriksen, 1960; Goldiamond, 1958). Chief among these criticisms was the argument that the investigators had improperly determined the thresholds in question, so that what appeared to be unconscious perception might well have been conscious perception after all. It did not help, either, that before World War II, the question of subliminal perception was raised mostly under the influence of psychoanalysis. After the war, the idea was revived as part of Bruner’s "New Look" in perception (Bruner & Klein, 1960), which was also influenced, to some degree, by psychoanalysis.13 There was also a vigorous debate, stimulated by Vance Packard's (1957) book, The Hidden Persuaders, over the role of subliminal messages in advertising. The New Look was a forerunner of the cognitive revolution, but the experimental psychology of the 1950s and early 1960s, dominated as it was by positivism and behaviorism, was not much interested in cognition -- and it was certainly not interested in anything tainted by psychoanalysis. Accordingly, the substantial body of evidence reviewed by reviewed by Adams and Dixon was largely dismissed and ignored.

Slide4.JPG (33440 bytes)That might have been the last we heard of subliminal perception, except that in the early 1980s Anthony Marcel (1983a; Marcel, 1983b) presented solid evidence of the phenomenon in research on semantic priming effects on lexical decision. In the lexical decision paradigm, the subject must decide whether a string of letters is an actual word in English. This is normally an easy task, but it is even easier if the target word is preceded by another, semantically related, word (Meyer & Schvaneveldt, 1971). This phenomenon is known as semantic priming, as distinct from the repetition priming studied in amnesic patients by Warrington and Weiskrantz (1970). Marcel's innovation was to present the prime surrounded by "masking" stimuli, so that it was rendered invisible to the subjects (the targets, though, remained completely visible). In one study Marcel (1983b, Experiment 5) varied the number of times the masked prime was repeated before the target was presented (there were other conditions in the experiment, but they are not relevant here). Attesting to the effectiveness of the masking procedure, detection of the primes was at chance levels, even when they had been presented 20 times. However, as illustrated in Figure 4,14 there was a clear semantic priming effect: lexical decision was speeded when the prime was semantically associated with the target word, compared to trials where prime and target were unrelated. This was the case even after a single presentation of the prime, and this effect grew with increasing numbers of repetitions. Thus, presentation of a prime such as nurse facilitated lexical decisions concerning semantically related targets such as doctor, even though the masking prevented subjects from consciously perceiving the prime itself.

A major strength of Marcel's research lay in his careful attention to the determination of thresholds. His report raised a firestorm anyway, with a number of critics essentially repeating the criticisms that had been raised against the earlier generations of research (e.g., Holender, 1986). I think this response occurred mostly because of the historical association of subliminal perception with psychoanalytic theory. But another reason was the simple fact that the cognitive theories of the time tended to describe cognition in terms of a series of ever more complicated processes, and had no room in them for the possibility that the meanings of words could be analyzed unless conscious attention was paid to them. The criticisms had the character of the apocryphal entomologist who found a bug he couldn't classify, so he stepped on it.15 Despite these criticisms, Marcel's findings were soon confirmed by others (e.g., Balota, 1983; Fowler, Wolford, Slade, & Tassinary, 1981), some of whom addressed the matter of thresholds even more assiduously then he did (e.g., Greenwald, Klinger, & Liu, 1989).16 These days, a wealth of evidence supports the validity of subliminal perception, defined broadly as the influence of stimuli that are too degraded by their conditions of presentation to be accessible to conscious perception. The debate over subliminal perception is not so much over whether it occurs, as over its extent.



The fourth line of research contributing to the rediscovery of the unconscious was hypnosis, a social interaction in which the subject acts on suggestions for experiences involving alterations in perception, memory, and the voluntary control of action. In fact, a case can be made that contemporary interest in unconscious processing arose in response to a single book, Divided Consciousness: Multiple Controls in Human Thought and Action, which took hypnosis as its major focus (Hilgard, 1977). Almost a century earlier, psychologists like William James (James, 1890/1980) had recognized that many of the phenomena of hypnosis involved a division in consciousness such that memories, percepts, and the like influence experience, thought, and action outside of phenomenal awareness. Hilgard put a modern spin on this earlier literature by reporting a series of carefully controlled experiments on suggested analgesia and other phenomena of hypnosis, and putting the research in the framework of modern cognitive theory.

For example, one of the earliest demonstrations of the dissociation between explicit and implicit memory occurred in a line of research on posthypnotic amnesia B the phenomenon which gave hypnosis its very name (J. F. Kihlstrom, 1985). After receiving appropriate suggestions, some individuals come out of hypnosis unable to remember the events and experiences which transpired while they were hypnotized -- an experience similar to the difficulty we all have, upon awakening, in remembering dreams and other events that transpired while we were asleep. People differ in their responsiveness to hypnotic suggestions, however, and posthypnotic amnesia is much more common in those who are highly hypnotizable (about 10-15% of the population), compared to those who are moderately hypnotizable or insusceptible to hypnosis.

One experiment classified subjects as low, medium, high, or very high in hypnotizability, on the basis of standardized tests devised for this purpose (J.F. Kihlstrom, 1980, Experiment 1). Regardless of their test scores, all subjects were treated as if they were hypnotizable. Following a standard induction of hypnosis, they memorized a list of 15 words; then they received a suggestion that, after coming out of hypnosis, they would be unable to remember what they did while they were hypnotized (posthypnotic amnesia does not occur unless it has been suggested by the hypnotist). When asked to recall the words they had memorized, the insusceptible subjects were able to do so readily, but the most highly hypnotizable subjects were densely amnesic, remembering less than a single word on average. After the amnesia suggestion was canceled, full recall was restored for all subjects.

Slide5.JPG (28017 bytes)While the amnesia suggestion was in force, the subjects received a free association test, in which they were asked to report the first three words that came to mind in response to cue words read aloud by the experimenter. The stimulus words were of two types: critical cues were semantically associated with words that the subjects had studied during hypnosis (e.g., the cue bread was associated with the studied item butter), while neutral cues were associated with target words that were entirely new (e.g., the cue ocean was associated with the target water, which had not been memorized). As Figure 517 shows, the subjects were more likely to respond with critical than neutral targets, providing another example of semantic priming. The most important finding, however, was that the magnitude of priming was the same in hypnotizable subjects, who did not remember having memorized the critical targets, as it was in insusceptible subjects, who remembered the learning experience clearly. Preserved priming shows that posthypnotic amnesia effects explicit memory, but spares implicit memory.

Slide6.JPG (26362 bytes)Hypnotic suggestion can also affect perceptual functions. When given hypnotic suggestions for blindness, for example, many hypnotizable subjects have the subjectively compelling experience that they no longer can see. However, Bryant and McConkey (1989) showed hypnotized subjects cards on which were printed a homophone (a word which has the same sound as another word but a different spelling, such as pain and pane) together with a disambiguating word (e.g., body or window). Other cards were shown to subjects when they were not hypnotically blind, and still other cards were not presented at all. The subjects did not see the cards shown during blindness, and as Figure 618 indicates, they were also unable to recall the words on these cards posthypnotically. However, on a subsequent spelling test they strongly tended to spell the homophones in accordance with the disambiguating context in which the words had been presented on the cards. This is another kind of semantic priming effect (Eich, 1984), because spelling performance is influenced by the semantic relation between the target word and its context. The fact that semantic priming occurred on the spelling test indicates that the words in question were processed by the subjects, despite the fact that they could not see them during hypnotic blindness.

redis29.gif (2998 bytes)Yet a third example of unconscious processing in hypnosis is provided by posthypnotic suggestion ‑- the phenomenon that, so our mythology tells us, gave Freud his first good insight into the psychological unconscious.  In some sense, posthypnotic suggestion is a special case of implicit memory, because subjects act on a suggestion given during hypnosis, despite the fact that they cannot remember the suggestion itself.  But posthypnotic suggestion is interesting in another way, because it is typically experienced as an involuntary, quasi-automatic response to the cue.  In a doctoral dissertation by Irene Hoyt, hypnotized subjects were given a posthypnotic suggestion to press a key whenever a particular number appeared on a computer screen.  After hypnosis was terminated, they were also instructed to press the key in response to a different number.  On some test trials, the posthypnotic suggestion and the waking instruction were put into conflict.  The posthypnotic suggestion did not always win out, once again shattering the myth of the coercive power of hypnosis. 

But the most important finding was that even when the two did not conflict, response to the posthypnotic suggestion interfered with response to the waking instruction, and vice-versa.  In other words, despite the experience and appearance of automaticity, processing the posthypnotic suggestion consumed a lot of cognitive resources.  Posthypnotic response is unconscious, in the sense that subjects are unaware of why they behave as they do, or even that they are behaving as they are; but it has had no opportunity to be automatized by extensive practice.

In some ways, the unconscious influences observed in posthypnotic amnesia and hypnotic blindness resemble those observed in the amnesic syndrome and blindsight, but there are important differences as well. In the first place, the impairments produced by brain damage are permanent, while the phenomena of hypnosis are reversible. But more important, hypnotized subjects are in no sense brain damaged. It might be possible to argue, on the basis of the amnesic syndrome and blindsight, that the basis of conscious recollection is in the hippocampus, and the basis of conscious vision is in the striate cortex. But in hypnotic subjects there is no question of damage to these areas. This means that our explanation of the distinction between conscious and unconscious mental life will have to do more than appeal to the involvement of particular brain centers.

Of course, the subjects in subliminal perception experiments are not brain-damaged either. But again there is a difference: just as hypnotic subjects are in no sense brain-damaged, the stimuli in hypnosis experiments are in no sense subliminal. In subliminal perception, by definition, the stimuli are severely degraded by the conditions of their presentation -- in Marcel's (1983b) case, by a masking stimulus presented, on average, less than 1/10 of a second after the prime. Similarly, studies of implicit memory in normal subjects typically involve degraded encoding conditions or extremely long retention intervals (Jacoby & Dallas, 1981); (Nelson, 1978). In posthypnotic amnesia, by contrast, the items in question are deeply encoded and and well retained (as indicated by the reversibility of the amnesia), and in hypnotic blindness the items are clearly perceptible to everyone but the subject. For these reasons, hypnosis offers a different perspective on unconscious mental life than that afforded by brain damage or subliminal stimulation.

Moreover, response to the hypnotist's suggestions often seems, both to the subject and to an outside observer, to be involuntary and almost compulsive in nature. For this reason the phenomena of hypnosis might seem to be variants on automaticity, but hypnotic behavior is by no means automatic.19 In cognitive psychology, automatic processes are usually held to be independent of intention, consume no attentional resources, and leave no trace of themselves in memory. But nothing happens in hypnosis unless the subject is actively engaged in what it going on; it is easy to demonstrate that response to hypnotic suggestions consumes attentional resources; and hypnotized individuals retain full awareness of what they have done, posthypnotically, unless they have received a specific suggestion for posthypnotic amnesia. Much as the amnesic syndrome, blindsight, and subliminal perception show that mental contents as well as processes can be unconscious, so hypnosis shows that processes can be unconscious even though they have not been automatized. Again, hypnosis is of interest because it affords a unique perspective on unconscious mental life.


The Psychological Unconscious Now

Earlier in the Principles, and perhaps with Hartmann in mind, James had offered a warning which would reverberate throughout the 20th century exploration of the unconscious:

The distinction between the unconscious and the conscious being of the mental state is the sovereign means for believing what one likes in psychology, and of turning what might become a science into a tumbling-ground for whimsies (1890/1980, Vol. 1, pp. 163).

James's criticism was prophetic, as we can see in the ensuing controversy, ranging across the entire 20th century, concerning Freud's psychoanalytic theory of mental life. Nevertheless, research on automaticity, neurological syndromes, "subliminal" perception, and hypnosis indicates that it is possible to document the dynamic effect of unconscious mental states and processes though rigorously controlled research. 

The rediscovery of the unconscious may have gotten a late start in psychology, but the study of unconscious mental life is now a growth industry in psychology. With a sophisticated, ever-enlarging understanding of cognitive processes, it is now possible to discuss unconscious mental life without making any substantive reference to Freud. Although there remain some skeptics, research on unconscious cognition now focuses less on existence proofs and more on analyses of its scope and limits. And research on unconscious emotion and motivation, modeled on studies of the cognitive unconscious, has begun to develop independent of psychoanalysis.


The Automaticity Juggernaut

In particular, the concept of automaticity, originating in the rather narrow confines of research on visual search and pattern recognition, has come to play an increasingly powerful role in personality, social, and clinical psychology. The general argument is that some attitudes, impressions, and other social judgments, as well as aggression, compliance, prejudice, and other social behaviors, are mediated by automatic processes which operate outside phenomenal awareness and voluntary control (e.g., John A. Bargh & Chartrand, 1999; Kirsch & Lynn, 1999a; Wegner & Wheatley, 1999).

To some extent, which I have come to think of as the automaticity juggernaut seems to represent a reaction to a cognitive view of social interaction which seems, to some, to inappropriately emphasize conscious, rational, cognitive processes, at the expense of the unconscious, irrational, emotive, and conative.  In addition, the popularity of automaticity seems to represent a reversion to earlier, pre-cognitive, situationist views within social psychology. 

After all, the concept of automaticity is at least tacitly modeled on innate stimulus-response connections such as reflexes, taxes, and instincts, as well as those acquired through classical and instrumental conditioning.  The automaticity juggernaut is not exactly a reversion to Skinnerian behaviorism, because it entails internal mental representations and processes intervening between stimulus and response, but it is close: if the cognitive processes underlying social cognition and social behavior are indeed largely automatic, then not too much thought has gone into them.


Repetition and Semantic Priming in Implicit Memory

Similarly, the concept of implicit memory has received a huge amount of attention in the field. A whole industry has developed around implicit memory, involving amnesic and demented neurological patients; dissociative disorders such as psychogenic amnesia, fugue, and multiple personality; children and the healthy aged; depressed patients receiving electroconvulsive therapy; surgical patients receiving general anesthesia or conscious sedation; and even college students who have all their wits about them (e.g., Roediger & McDermott, 1993; Schacter, Chiu, & Ochsner, 1993). Rather than focusing on existence proofs -- which is still somewhat the situation for subliminal perception (see, e.g., Draine & Greenwald, 1998) -- the implicit memory literature assumes at the outset that the notion of unconscious, dynamically active memories is fundamentally valid, and focuses instead on the mechanisms by which unconscious memories are dissociated from conscious recollection.

Still, there are some important issues that have to be addressed by further research.  For example, almost all the evidence on implicit memory has been collected within a single narrow paradigm, repetition priming, leading to theories of implicit memory which emphasize relatively low-level perceptual processes.  But semantic priming occurs too, not just in posthypnotic amnesia but in organic amnesia as well, suggesting that these perception-based theories are not adequate to the phenomenon.  Similarly, while explicit and implicit memory are dissociable, they also interact, requiring revisions in theories which hold that these two expressions of memory are mediated by separate memory systems in the brain (Kihlstrom, 1998c).

Despite these and other persisting questions, the general acceptance of the distinction between explicit, conscious and implicit, unconscious expressions of memory opens the door to extensions of the explicit-implicit distinction to other domains of mental life, across the whole of Kant's trilogy of mind - -cognition, emotion, and motivation.  



The Cognitive Unconscious

Beyond automaticity, the general acceptance of the distinction between explicit, conscious and implicit, unconscious expressions of memory opens the door to extensions of the explicit-implicit distinction to other domains of cognition.


Implicit Perception

By analogy to implicit memory, my co-authors and I have defined implicit perception as the influence of a current event, or an event in the very recent past -- what William James (James, 1890/1980) called the specious present -- on experience, thought, or action, in the absence of conscious perception of that event (J.F. Kihlstrom, Barnhardt, & Tataryn, 1992a). Implicit perception subsumes so-called "subliminal" perception, involving the processing of stimuli which are degraded beyond conscious perception by low intensities, brief durations, or masking stimuli. But it goes beyond the subliminal to include neurological syndromes such as blindsight and visuo-spatial neglect, where the stimuli are in no sense subliminal: they are perfectly visible to everyone but the brain-damaged subject. So too, in the conversion syndromes of "hysterical" deafness, blindness, and anesthesia, where there is no brain damage. Similarly in hypnotic blindness, deafness, anesthesia, and analgesia: the subjects would be clearly aware of the stimuli in question were it not for the hypnotist's suggestion. On the fringes of consciousness, are cases of so-called preattentive processing, where the stimulus in question is nominally supraliminal, but escapes focal awareness by virtue of parafoveal presentation, or presentation over the unattended channel in the dichotic listening or shadowing paradigm.

What all of these phenomena have in common is a dissociation between explicit and implicit perception, analogous to the dissociation between explicit and implicit memory: the subject's experience, thought, and action is affected by some event in the current stimulus environment, in the absence of conscious perception. In this way, the term implicit perception captures a broader range of phenomena than is covered by the term subliminal perception, because it covers the processing, outside of conscious awareness, of stimulus events which are clearly perceptible in terms of intensity, duration, and other characteristics. The label also has the extra advantage of skirting the difficult psychophysical concept of the limen.

The distinction between implicit perception and implicit memory is not always easy to make, because both phenomena are revealed by post-exposure priming effects of various sorts -- that is, by performance on nominal tests of implicit memory (J.F. Kihlstrom, 1996a). Schacter's (1987) seminal review of the implicit memory literature referred to both Weiskrantz's (1986) studies of blindsight and Marcel's (Marcel, 1983a, 1983b) experiments on subliminal perception. In my view, however, the term implicit memory should be reserved for cases where there is no question that the stimulus event was consciously perceived at the time of encoding. Where there is no conscious awareness at the time of encoding, then we can consider priming effects as evidence of implicit perception: Prior perception is logically implied by spared implicit memory. Thus, on the assumption that adequately anesthetized patients are really unaware, during their procedures, of what our medical colleagues disarmingly call "surgical stimuli", evidence collected in the recovery room of priming effects attributable to events presented during surgery constitutes evidence of implicit perception, not just implicit memory. By contrast, priming effects observed in conscious sedation, where subjects are fully aware of the study trials, is a pure implicit memory effect.

Adopting the implicit-explicit distinction may help resolve a persisting controversy over the scope of unconscious perception. For example, Greenwald (1992) and his colleagues have asserted that subliminal perception is analytically limited B some semantic processing of a subliminal stimulus is possible, but not too much of it. On the other hand, other enthusiasts of subliminal stimulation, including those who employ subliminal techniques in advertising and psychotherapy, assume more processing than Greenwald's arguments would allow. For example, the psychoanalyst Lloyd Silverman (Silverman, 1976; Silverman & Weinberg, 1985) reported that subliminal symbiotic stimulation B by which he meant subliminal presentation of the phrase Mommy and I are one -- had profound effects on the behavior of both normal subjects and psychiatric patients. For this to be true, subliminal perception would have to possess almost Hartmanian cognitive scope, extending to complex semantic analyses far beyond the relatively simple ones permitted under Greenwald’s view.

My own view is that Greenwald is right, so far as truly subliminal stimulation goes (J.F. Kihlstrom, Barnhardt, & Tataryn, 1992b), and arguments to the contrary are based more on the Romantic or psychoanalytic notions of the unconscious that I discussed earlier. On the other hand, there are lots of ways to render percepts implicit, and how it is done may make a big difference to what you can do with them. Merikle and Reingold (1988) have usefully distinguished between the objective threshold, where all response to the stimulus drops to chance levels, and the subjective threshold, where the subject simply does not experience the stimulus consciously. Experiments such as Greenwald's experiments take subjects as close to the objective threshold as they can get (Draine & Greenwald, 1998; Greenwald, Draine, & Abrams, 1996; Greenwald et al., 1989), and with such degraded presentations it is not surprising that perception, and memory encoding, are analytically limited. When presentation conditions get closer to the subjective threshold, or with the parafoveal presentation of supraliminal stimuli, more extensive analyses, still outside awareness, might be possible. In hysteria and hypnosis, where the stimulus is in no sense degraded and lies within the scope of focal attention, the possibilities for unconscious analysis might be virtually unlimited.


Implicit Learning

Continuing the elaboration of the explicit-implicit distinction to other domains, we can define implicit learning as the acquisition of new knowledge and patterns of behavior through experience, in the absence of awareness of the knowledge or behavior so acquired. As it happens, the term "implicit learning" antedates implicit memory, having been coined by Arthur Reber in 1967. In his now-classic experiments, Reber (1967) asked subjects to memorize a set of letter strings, such as


Slide7.JPG (20822 bytes)He then informed his subjects that the strings they had studied had all been by generated by a particular set of rules -- namely the "Markov process" artificial grammar depicted in Figure 7.20 When asked to describe the grammar, none of Reber's subjects could do so. Nevertheless, the subjects were able to distinguish between new letter strings that conformed to the grammar, such as


and other strings that did not, such as


Their performance on the discrimination task revealed that the subjects had acquired knowledge of the grammar, without being able to articulate the grammar in question. Implicit learning of this sort has also been observed in a wide variety of other paradigms, including classical and instrumental conditioning, control of complex systems, and the learning of categories and sequential relationships (for a review, see Berry & Dienes, 1993). In each of these cases, people's behavior is altered by prior experience B the classical definition of learning -- even though they are unaware of what they have learned.

According to Reber, the learning displayed by his subjects was implicit in two senses: they acquired new knowledge incidentally, without intending to do so (they had been asked to memorize letter strings, not to induce a set of rules); more important, they did not know what they knew (they lacked the ability to consciously articulate the grammar in question). In his view, the learning of artificial grammars is a laboratory model of the process by which natural language is unconsciously acquired and used. We speak and understand our native language without consciously reflecting on the grammatical rules that our language follows, and we learn these rules simply by virtue of exposure to our native language. Similarly, linguists operating in the Chomskian tradition hold that syntax language acquisition occurs unconsciously and automatically by virtue of a language-specific cognitive module that evolved specifically for that purpose. In Reber's view, however, implicit learning is mediated by a general-purpose learning module that is not specific to language, and which allows the organism to pick up a wide variety of regularities in the environment. Language acquisition, far from being unique, is a special case of this general learning process.

As with implicit perception, the border between implicit learning and implicit memory is a little vague (J.F. Kihlstrom, 1996a). Of course, this is as it should be: memory provides the cognitive basis for learning in the first place, and whatever is learned has to be stored in memory. Both implicit learning and implicit learning meet the definition of "any change in experience, thought, and action attributable to a past event, independent of conscious recollection of that event". But the problem goes deeper than that. In the first place, priming effects generally result from a single exposure to the priming event -- a more or less discrete episode in memory. However, implicit learning generally occurs over a sequence of trials -- each constituting a different episode in memory.

Of course, the learning episode is also an experience in the subject's life. When normal subjects learn an artificial grammar, they certainly remember being asked to study the sample strings, and they may even remember the strings themselves, even if they are unaware that the strings follow some rule, or that they have unintentionally abstracted some rule from the studied items. By contrast, when brain-damaged amnesic patients acquire new patterns of behavior from experience, they are amnesic for the whole learning experience. For example, the famous patient H.M. was able to acquire a number of motor skills, as shown by progressive improvements in such tasks as pursuit-rotor learning and mirror-tracing; but despite these improvements, he failed to recognize these tasks as ones he had performed previously (Milner, Corkin, & Teuber, 1968). In amnesia, the occurrence of implicit learning also gives evidence of preserved implicit memory, but I prefer to reserve the term implicit memory for effects that occur in the absence of conscious memory for the original experience. By the same token, I reserve implicit learning for abilities and patterns of response that are acquired through learning experiences, in the absence of conscious awareness of what has been learned.

At this point, a small industry has developed around implicit learning -- culminating in the publication of a whole "handbook" devoted to the topic (Stadler & Frensch, 1998). Still, it has to be said that the claim of implicit learning remains controversial even after more than 30 years of work. There is a continuing debate over whether implicit learning is really unconscious in any meaningful sense of the term. It just may be too much to expect subjects to be able to articulate an entire Markov-process of the sort illustrated in Figure 7, but subjects might be consciously aware of just enough of the system to permit them to discriminate at above-chance levels between grammatical and ungrammatical strings.

There is also a question about the format in which the knowledge acquired by the subjects is represented. Perhaps, as implied by the original artificial grammar studies, the subject acquires a whole system of If-Then productions and this procedural knowledge, like all procedural knowledge, is inaccessible to conscious introspection. On the other hand, perhaps the knowledge is not procedural at all, but declarative in nature. For example, subjects might abstract from the learning trials a prototype of a grammatical string; alternatively, they may simply memorize the instances on the study list. In either case, they may make relatively accurate grammaticality judgments by consciously comparing test items to the summary prototype, or to the specific exemplars they have memorized. We just do not yet know the answer. But what we do know is that amnesic patients can learn from their experience without remembering the learning experience itself, and in that sense, at least, implicit learning gives evidence of unconscious influence.


Implicit Thought

If the concept of implicit learning is more controversial than those of implicit memory or implicit perception, the concept of implicit thought is even more so. Still, the literature contains some favorable evidence, if only just a little. For example, some years ago Kenneth Bowers and his associates found that subjects can choose which of two problems is soluble without knowing the answer to the soluble one (Bowers, Regehr, Balthazard, & Parker, 1990). In some of their research, Bowers et al. employed a modification of the Remote Associates Test (RAT) (Mednick, 1962), used in the study of creativity, which they called "Dyads of Triads" (DOT). In the RAT, subjects are presented with three words, such as:






and are asked to respond with a fourth word which is associated with each of the previous three (in this case, SALT). In the DOT, subjects are presented with two RAT-like word sets, such as:











redis44.gif (5100 bytes)One triad coheres on a common (if remote) associate (i.e., CARD), while the other one (barring psychotically loose associations!) does not. The subjects are asked to generate the associate for the coherent set; failing that, they are to guess which triad is the coherent one. Even when they could not say what the solution was, across five studies Bowers et al. found that subjects correctly chose the coherent triad about 58% of the time -- significantly better than would be expected by chance. They obtained similar results on other experiments, where subjects were presented with picture fragments, and asked to indicate which set could be reassembled to form a coherent image.

redis45.gif (5612 bytes)In a doctoral dissertation, Victor Shamas (nee Shames) found ath soluble RAT items primed their solution words for lexical decision, even when the subject failed to produce the solution itself.

The above-chance "guessing" performance of Bowers' subjects seems to be a kind of semantic priming effect. Reading each of the stimulus items will prime the semantically related target item in memory, just as doctor primed nurse in Marcel's (1983b) lexical decision task. Presumably, if the amount of priming crossed some threshold of activation, subjects could report the solution to the problem. Presumably, there is a kind of subthreshold, preconscious level of activation which, while insufficient for conscious awareness, is enough to push the subjects' choice behavior in the right direction. But what kind of priming is it? Because the stimulus items remain clearly visible while the subject tries to solve the problem, memory is irrelevant, so the priming effect cannot be classified as implicit memory. For the same reason, it cannot count as implicit perception, either. Nor can it be classified as implicit learning: no items are repeated, and there is no feedback telling the subjects whether their choices are right.

redis47.gif (3028 bytes)In the Bowers et al. experiment, what is being primed is the solution to a problem. The mental representation in question is neither a percept nor a memory, but rather an idea or an image -- in the broadest sense, it is a thought. By analogy with implicit memory, my colleagues and I have defined implicit thought as the influence of some cognitive representation, itself neither a percept nor an episodic memory, on experience, thought or action, in the absence of conscious awareness of that representation (Dorfman, Shames, & Kihlstrom, 1996; J.F. Kihlstrom, Shames, & Dorfman, 1996). Implicit thought may well underlie some of the most interesting facets of creative thought. In my view, intuition reflects a priming-based "feeling of knowing" similar to what we commonly see in studies of memory (Hart, 1965; Nelson, Gerler, & Narens, 1984); incubation reflects the gradual accumulation of strength of this primed idea; and insight reflects the emergence of the preconscious idea into the full daylight of consciousness.


Beyond the Cognitive Unconscious

Along with automaticity, implicit memory, implicit perception, implicit learning, and implicit thought comprise the cognitive unconscious (J.F. Kihlstrom, 1987).21 But cognition is not all there is to mental life: there is emotion and motivation as well (Hilgard, 1980). Accordingly, we are led to ask whether there is an affective unconscious, involving emotional feeling states, and a conative unconscious, involving motivational drives and goals, as well. Of course, emotional and motivational states may arise automatically, and in that sense result from unconscious processes. Many of the applications of automaticity to personality, social, and clinical psychology make just this argument (e.g., J. A. Bargh, 1990; Zajonc, 1980, 1984). But can emotions and motives be unconscious, in the same way that memories can, and still dynamically influence our behavior? We are admittedly verging near Freudian territory here, but once one has accepted the evidence for implicit memory and other aspects of the cognitive unconscious, one must at least entertain the possibility that other mental states, including noncognitive states such as feelings and desires, can also be unconscious.

Of course, putting the question this way assumes that emotions and motivations are different from cognitions. There is a school of thought within cognitive psychology and cognitive science that denies that this is the case (we might call this view cognitive hegemony). Put bluntly, this school, whose roots go back to Aristotle, holds that our feelings and desires are cognitive constructions -- beliefs about what we feel (Schachter & Singer, 1962) and what we desire (Lepper, Greene, & Nisbett, 1973). If emotional and motivational states are simply variants on cognitive states, and cognitive states can be unconscious (as in the case of implicit memories), then it follows logically that emotional and motivational states can be unconscious as well. On the contrary, if -- as Immanuel Kant argued -- "there are three irreducible faculties of mind: knowledge, feeling, and desire", and emotional and motivational states are not reducible to cognitive states, then questions about unconscious emotion and motivation must be answered on their own grounds.


The Affective Unconscious

Turning first to the affective domain, my collaborators and I have proposed that we seek dissociations between explicit and implicit emotions (J.F. Kihlstrom, Mulvaney, Tobias, & Tobis, 2000). Again paralleling the vocabulary of the cognitive unconscious, we define explicit emotion as the person's conscious awareness of an emotion, feeling, or mood state; implicit emotion, then, refers to changes in experience, thought, or action which are attributable to one's emotional state, in the absence of conscious awareness of that state.

Emotion as an Expression of Implicit Cognition. Of course, it is well known that conscious emotional responses can serve as expressions of implicit memory and perception, Most of the relevant studies make use of the mere exposure (Zajonc, 1968), in which prior exposure to an object increases one's preference for that object on a subsequent choice task. According to one class of theories, the mere exposure effect is a result of the repetition priming effect already familiar from studies of implicit memory and implicit perception. The initial exposure creates, or activates, representations of the stimulus in memory. When on a later occasion the person has to make a preference judgment about the same object, the resulting memory-based feeling of familiarity increases likability. There is a similar repetition effect on judgments of truth (Schwartz, 1982), and the underlying mechanism is probably the same.

On the memory side, it seems that brain-damaged, amnesic patients show the mere exposure effect, even though they cannot consciously remember the objects to which they had previously been exposed (Johnson, Kim, & Risse, 1985). And in the study that really got the affective revolution going (Zajonc, 1980), Kunst-Wilson and Zajonc (1980) found that normal subjects showed mere exposure effects even when the exposures in question were subliminal, and thus not consciously perceived. Subsequent research has indicated that the subliminal mere exposure effect may be even more powerful than the supraliminal one (R. F. Bornstein, 1989, 1992). In both cases, the subjects knew what they liked, but did not know why. Their feelings are a little reminiscent, if in reverse, of those expressed by the 17th-century English satirical poet, Thomas Brown:22

I do not love thee, Dr. Fell.

Why I cannot tell.

I only know

I do not love thee, Dr. Fell.


The idea that emotional responses can reflect implicit memory is at least as old as Breuer and Freud (1893-1895/1953), whose hysterics "suffered from reminiscences" of previous traumatic events. More recently it has been revived as part of what has been called the trauma-memory argument -- that memory traces of traumatic events, inaccessible to conscious recollection, may nonetheless influence the victim's experience, thought, and action in the form of pathological symptoms (J.F. Kihlstrom, 1995, 1996b, 1997, 1998a). For example, Frederickson has distinguished between consciously accessible recall memories and unconscious feeling memories of trauma (Fredrickson, 1992). As she writes, "feeling memory is often experienced as a flood of inexplicable emotion…. These clients are experiencing a feeling memory about being abused, even though… they can recall nothing about their abuse" (p. 92).

The notion of "feeling memories" finds some support from the literature on emotion as an expression of implicit memory, but some clinicians erroneously infer a history of trauma from their patients' reports of inexplicable feelings, and then engage in therapeutic practices, sometimes called recovered memory therapy, designed to restore traumatic memories to conscious recollection (J.F. Kihlstrom, 1996b, 1997, 1998a; Shobe & Kihlstrom, 1997). Unfortunately, a link between some past event and a person's current emotional state can be made only when there is independent corroboration of the event in question (J.F. Kihlstrom, 1997). When there is no independent corroboration of the traumatic event, however, clinical inferences of past trauma violate the logic of implicit memory, and can lead therapist and patient onto the dangerous ground of false memory syndrome (J.F. Kihlstrom, 1998a).

Slide8.JPG (30819 bytes)Implicit Emotion. With respect to the proposition that people can be unaware of emotional states, which nonetheless influence their ongoing experience, thought, and action, the empirical evidence is regrettably sparse. In fact, some theorists assert that the idea of unconscious emotion is a contradiction in terms (e.g., Clore, 1994). However, there are good theoretical reasons for thinking that it might be true. For example, Peter Lang's (1968) multiple-systems theory of emotion postulates that every emotional response consists of three components: verbal-cognitive, corresponding to a subjective feeling state such as fear; overt motor, corresponding to a behavioral response such as escape or avoidance; and covert physiological, corresponding to a change in some autonomic index such as skin conductance or heart rate (see Figure 8).23 These three components or systems usually covary, but under some circumstances they can move in different directions B a state which Rachman and Hodgson have labeled desynchrony (Rachman & Hodgson, 1974). Desynchrony comes in several forms, but the one that is relevant in the present context occurs when explicit emotion, as represented by a person's conscious, subjective feeling state, is absent, but the person nevertheless shows recognizable behavioral and somatic signs of implicit emotion.

Slide9.JPG (37872 bytes)Empirical evidence for this particular form of desynchrony is sparse, and rarely goes beyond clinical anecdote (J.F. Kihlstrom et al., 2000), but at least it is predicted by a well-established neuropsychological model of fear proposed by LeDoux (1996). As illustrated in Figure 9,24 LeDoux proposes that environmental stimuli are first processed by sensory centers in the thalamus, which then pass information about emotional events to the amygdala, which in turn generates appropriate behavioral, autonomic, and endocrine responses. Information about these responses is also passed to cortical centers supporting working memory, where it is integrated with information provided by thalamic centers about the fear stimulus, thus generating the full-blown subjective experience of being afraid of something

redis56.gif (4091 bytes) However, a disconnection between thalamus and cortex will prevent the fear-eliciting stimulus from being represented in working memory. As a result, the person will experience fear without being aware of the fear stimulus. In this case, emotion will serve as an implicit expression of perception or memory, as described earlier. 


redis57.gif (3370 bytes) Alternatively, if there is a disconnection between the amygdala and the cerebral cortex, the person will behave in a fearful manner without feeling fear or anxiety. In this case, there will be a dissociation between explicit and implicit emotion.


Neuroscientific theory aside, a potentially interesting approach to implicit emotion has been offered by Greenwald and Banaji (1995) in their application of the explicit-implicit distinction to the social-psychological concept of attitude. In traditional social-psychological theory, attitudes are defined as affective dispositions to like or dislike certain things, and they are usually measured explicitly by self-report scales. In other words, the traditional concept of attitude is of a conscious feeling state -- an explicit emotion. However, Greenwald and Banaji have suggested that people may possess positive and negative implicit attitudes about themselves and other people, which can also affect ongoing social behavior outside of conscious awareness. Implicit attitudes are assessed in terms of task performance rather than self-report. When they diverge from their explicitly expressed counterparts, we have evidence for a dissociation between explicit and implicit emotion. Unfortunately, the experimental literature on implicit attitudes rarely offers a direct contrast with between explicit attitudes, so we don't yet know whether such dissociations actually occur, in what kinds of people, and under what circumstances. Still this experimental approach to implicit emotion is very promising.


The Conative Unconscious

Slide10.JPG (30094 bytes)On the motivational side, the late David McClelland and his associates have articulated a concept of implicit motives B interestingly, without overt reference to the concept of implicit memory (McClelland, 1980; McClelland, Koestner, & Weinberger, 1989). In parallel with the now-familiar distinction between explicit and implicit memory, explicit motivation may be defined as the conscious representation of a conative state, or the desire to engage in some particular activity, as represented by a craving for food, yearning for love, and the like. By contrast, implicit motivation refers to any change in experience, thought, or action that is attributable to one's motivational state, in the absence of conscious awareness of that state. For McClelland and his colleagues, explicit motives are self-attributed: the person is aware of the motive, can reflect on it, and can report its presence in interviews or on personality questionnaires. For example, the need Achievement subscale of the Personality Research Form (PRF) a widely used multivariate personality inventory, includes such items as "I enjoy doing things which challenge me" or "I will keep working on a problem after others have given up". Subjects' responses on such tests reflect their awareness of what they want, what their goals are, and what drives them. Implicit motives, by contrast, may be inferred from the person's performance on such tasks as the Thematic Apperception Test (TAT), a classical "projective" test of personality. In the TAT, subjects are asked to make up stores in response to ambiguous pictures, and these stories are coded for various themes. For example, in response the picture in Figure 10,25 one subject might talk about how the boy is being forced to practice the violin, when in fact he would rather be out playing baseball; another subject might say that he is suffering stage fright before a school performance in front of his parents; another that he is a child prodigy, supremely confident, about to premiere a new concerto before the crowned heads of Europe. In theory, the motives attributed to the characters in the picture are unconscious projections of the subject's own motives.26

We are admittedly verging near Freudian territory here, but the motives in question are not seething sexual and aggressive impulses arising from the id; they are motives for achievement, power, affiliation, and intimacy. 

On the basis of an extensive program of empirical research, McClelland and his associates concluded that explicit and implicit motives differ in a number of ways. Explicit motives are strongly tied to prevailing social norms, while implicit motives are more likely to diverge from what significant others say we should desire. Explicit motives are correlated with the choices that people make over the short run, while implicit motives are associated with long-term behavioral trends. Explicit motives are aroused by extrinsic social demands, while implicit motives are aroused by intrinsic task incentives. These differences are analogous to the dissociations found between explicit and implicit memories, and they suggest that we can be engaged in motivated, goal-oriented behavior without being aware of what our motives are.

Still, there are some serious methodological problems to be solved before we can accept this conclusion with confidence. The means by which explicit and implicit motives are assessed are so different that we cannot be confident that the fundamental distinction has to do with awareness. For example, the PRF and TAT may assess different motives, even though their scales have the same names. If so, it would not be surprising that they correlated with different classes of behavior. Moreover, it has not been demonstrated that people are unaware of their motives, as assessed by the TAT. The subject who projects high achievement motivation on the boy in the figure may be perfectly well aware of his own achievement motivation. Proper documentation of a dissociation between explicit and implicit motivation requires that subjects be unaware of the motives which implicitly influence their experience, thought, and action. The literature on implicit motivation rarely asks this question, and it must be satisfactorily addressed before we know what to make of implicit motives.


Quo Vadis?

At the end of the 18th century, Immanuel Kant marvelled at the apparent contradiction between having ideas, yet not being conscious of them. In response, we can now say that studies of priming and other effects show us conclusively that unconscious ideas (and perhaps feelings and desires as well) exist, and that they affect our behavior. At the end of the 19th century, William James cautioned that the idea of the unconscious was a license to believe whatever one likes in psychology. In response, we can say that the criteria for automaticity and for priming and other methodologies, all rigorously applied, will strongly constrain our inferences about unconscious contents and processes. 

For example, the scope of the psychological unconscious, broad as it is, does not appear to be so broad as to encompass the primitive, infantile, irrational unconscious of Freud's psychoanalytic theory. There is no evidence, in any of the science I have summarized today, favoring Freud’s view that the unconscious is the repository of primitive, infantile, irrational, sexual and aggressive impulses, repressed in a defensive maneuver to avoid conflict and anxiety. 

Nor is there evidence that subliminal influences have special power to influence what people think, feel, want, and do. 

Nor is there any evidence to support clinical lore concerning unconscious representations of trauma, or the excesses of the recovered memory movement in psychotherapy. In this last case, as James warned, the unconscious does indeed seem to be a tumbling-ground for whimsies.

Over the last two or three decades, much has been learned about the unconscious mind. The remainder of this book lays out the evidence for unconscious processing, describing what is known about the psychological unconscious and how we know it. In my view, there is incontrovertible evidence for the automatic operation of certain mental processes and for the dynamic influence of implicit memories. Implicit perception is, perhaps, less convincingly established at this point, and implicit learning remains controversial as well. Still the evidence favoring both concepts cannot be dismissed out of hand. Research on implicit thought is admittedly immature, but the evidence cries out for further investigation. Based on the evidence for the cognitive unconscious, the twin ideas implicit motivation and implicit emotion are also viable, but we still require convincing evidence that they can be dissociated from their explicit counterparts.

At the same time, the rediscovery of the unconscious is not complete. We stand, like Lewis and Clark at St. Louis in 1803, on the edge of a territory whose outlines are well known, but whose interior detail is rather obscure. In addition to summarizing what has been learned, in this book I will also offer suggestions in which future research -- my own and others' -- might profitably go.

At this point, however, the evidence for unconscious mental life is so vast, so convincing, increasing and strengthening so much with each new issue of our best journals, that we are in danger of coming full circle, to the position of conscious inessentialism that Owen Flanagan has discussed. Some philosophers and psychologists have concluded that automaticity and priming dominate our behavior, so that consciousness is an illusion -- at best a commentary on what is going on down below, at worst a delusion that gets in the way of adaptive action (not to mention a proper scientific understanding of mind and behavior). I think we see this trend clearly in the "automaticity juggernaut" that I described earlier. As someone who has devoted virtually his entire career to getting people to take the psychological unconscious seriously, I am reminded of Aesop's warning: we should be careful of what we pray for, because we just might get it.

As a fervent supporter of the cognitive revolution in psychology, I am reminded that the French revolution of 1789 replaced one despotism with another. Is this what we overthrew behaviorism for -- To be told that we are automatons after all? Is this why we rejected psychoanalysis -- To be told that we really don't know what we are doing, or why? Is this why we have developed brain-imaging techniques to explore the links between body and mind -- That consciousness is a charming feature of human brain activity, but that in the final analysis it doesn't buy us anything?

I don't think so. Like language and intelligence, consciousness is too great an achievement of human evolution to be useless, much less maladaptive. Consciousness allows us to be aware of the present, and to reflect on our past, so we can plan for our futures. Without consciousness there can be no culture -- no way of deliberately sharing our knowledge, experiences, and ideas with others of our species, so that we can promote our cultural evolution into a higher form of life. We now know that the psychological unconscious is real and dynamically active. But so is consciousness, and if we ignore this central fact of human existence we will never achieve a satisfactory science of mental life. This book is about the unconscious mind, not about consciousness. But at the end of the book, I will try to say what the unconscious mind tells us about consciousness itself -- what it is good for, and where it comes from.




1These methods are described by Palmer (1999).  Return to text.

2According to Weber's Law, dI / I = C, the change in intensity needed to produce a JND is a constant proportion of the original intensity.  According to Fechner's Law, S = klogI, perceived intensity varies as a logarithmic function of physical intensity.  According to Stevens' Law, S=kIN, perceived intensity varies as an exponential function of physical intensity (Stevens, 1961) .  For an overview of the psychophysical laws as they apply to vision, see Palmer (1999, Appendix A)Return to text.

3Similarly, there appear to be four basic tastes (sweet, sour, salty, and bitter); a fifth basic taste, glutamate, appears in certain hearty foods such as soy sauce.  And there appear to be six basic smells (spicy, fragrant, ethereal, resinous, putrid, and burned).  In principle, at least, there is a different neural system underlying each of these basic dimensions of taste and smell, just as there is a different neural system underlying the four "psychological primaries" in color.  One of the problems with introspection has to do with cultural biases in the stimulus materials presented to subjects for introspection.  Although Euro-American psychophysics converged on four basic tastes, as long ago as 1908 a Japanese investigator, Kikunae Ikeda, argued for a fifth basic taste, umami, or “savory”, roughly corresponding to the flavor of soy sauce.  In February 2000, neuroscientists at the University of Miami, led by Nirupa Chaudhari, isolated receptors in the taste buds of the tongue that are specifically sensitive to glutamate, the chemical in umami.  In should be noted that the structuralists were not just interested in sensation.  Wundt's argument that there are three basic dimensions of feeling (pleasntness-unpleasantness, excitement-calm, and strain-relaxation) lies at the heart of a debate over the structure of emotion that has persisted into the 21st century (e.g., Green, Goldman, & Salovey, 1993; Green & Salovey, 1999; Tellegen, Watson, & Clark, 1999a, 1999b)Return to text.

4I can only scratch the surface of pre-Freudian notions of unconscious mental life here.  The topic is covered definitively by Ellenberger (1970) .  Whyte (1960) is especially valuable for literary and philosophical sources.  Klein (1977) is extremely critical of the whole notion of the unconscious, as indicated by his title; the book is essentially an attack on both Whyte and Ellenberger.  One wonders, though, what his attitude might have been had it not been colored by the excesses of von Hartmann and Freud. Return to text.

5Kant defined anthropology broadly as "knowledge of mankind".  His Anthropology stands as the first textbook of psychology in a form we would recognize today, beginning with an analysis of the "cognitive faculty", including consciousness and imagery, continuing with emotion and motivation, and ending with remarks on personality, sex differences, and the effects of race and ethnicity (Hatfield, 1998; J.F. Kihlstrom, 1998b) . Return to text.

6According to Wozniak (Wozniak, 1992) , Wilhelm Wundt, who was Helmholtz’s assistant at the Physiological Institute at Heidelberg, independeltly discussed the role of unconscious inferential and integrative processes in perception.  See, especially, the introduction to Wundt  (1862/1961)Return to text.

7Schematic depiction of the size-distance relation underlying the phenomenon of size constancy in visual perception.  Objects A and B differ in size, but because of their differing distances from the observer cast images of the same size on the observer’s retina.  Objects A and A’ are of the same size, but their retinal images differ in size.  For a thorough discussion, see Palmer (1999), Chapter 5.  Return to text.

8An alternative account of size constancy has been offered by Gibson (e.g., 1979).  For Gibson, perception needs no inferences of any kind, conscious or unconscious.  Rather, Gibson argues that size constancy is perceived directly from a higher-order pattern of stimulation -- namely, the ratio of the retinal size of the object to the retinal size of surrounding stimuli; this ratio remains constant as objects approach or move away from an observer. I am not arguing for Helmholtz's view of size constancy over Gibson's (though, frankly, I do prefer the former to the latter), but only using the phenomenon to illustrate what Helmholtz meant by unconscious inferences.  Return to text.

9The sole source for this self-serving anecdote is Jones himself, whose image of Freud's solitary pursuit of truth against the prejudices of conventional thinking has been severely undermined by more recent scholarship (e.g., M. Macmillan, 1991/1997)Return to text.

10The role of psychoanalytic ego psychology in maintaining an interest in cognition during the darkest days of behaviorism is nowhere better illustrated than in a paper on imagery by R.R. Holt (1964)Return to text.

11Illustration of the basic procedure for inducing the Stroop effect.  In the first column, color words are printed in ink of the color they represent.  In the second column, color words are printed in ink of a different color.  Return to text.

12Performance of amnesic patients and controls on three tests of memory. After Warrington & Weiskrantz (1970), Table 3.  Return to text.

13See footnote 8.  In fact, Bruner’s co-author, George S. Klein, was (along with Heinz Hartmann and David Rapaport), one of the leaders in the ego-psychological movement within psychoanalysis (G. S. Klein, 1976). Return to text.

14Masked semantic priming of lexical decision.  After Marcel (1983a), Experiment 5, Table 7.  Results are shown from the condition employing a 500 msec ISI.  Return to text.

15I first heard this description applied by the late E.R. Hilgard to T.X. Barber in a debate (possibly at the 1970 meeting of the American Psychological Association) over the nature of hypnosis.  Return to text.

16It may seem strange to report the study of Fowler et al. as a "replication" of a study by Marcel which was published two years earlier.  However, the anomaly arises from the exigencies of the publication process.  Marcel first announced his findings in at a scientific meeting held in 1974 and published a brief account of them in 1980, though formal publication of his complete report was delayed until 1983.  Return to text.

17Semantic priming on a word-association test administered during posthypnotic amnesia. After Kihlstrom (1980), Experiment 1, comparing subjects of low and very high hypnotizability (controls and amnesics, respectively).  Free recall data from Table 2.  Free association data from Table 3, targets elicited as first associates only.  Baseline for free association to neutral items calculated by averaging across all subjects in the experiment, regardless of hypnotizability.  Return to text.

18Proportion of targets produced on a test of free recall and on a test of homophone spelling.  All of the targets were presented visually, but some of the targets were unseen by subjects due to hypnotic suggestions for selective blindness.  Data from Bryant & McConkey (1989c), Table 1, Experiment 1.  Return to text.

19Actually, there are a number of contemporary theorists who claim that hypnotic behavior is automatic (e.g., Kirsch, 2001; Kirsch & Lynn, 1998, 1999b; Woody & Bowers, 1994) , but for reasons elaborated elsewhere (J.F. Kihlstrom, 1992) I think they’re wrong.  Return to text.

20A "Markov process" artificial grammar of the type studied by Reber (1967).  The process begins at the point labeled #0, meaning that the first letter in a grammatical string must be either an M or a V.  If the first letter is an M, then the second letter must be an S; this S may repeat, or the next letter must be a V, which can be followed by either an R or an S.  If the first letter was a V, then the next letter must be X, which may be followed by either an S or an R, either of which may repeat.  The last letter of a grammatical string is either S or M, after which the process terminates at #5.  Return to text.

21I re-introduced this term in my 1987 Science paper, following the example of Razran (1961) and Rozin (1976)Return to text.

22Brown, in turn, was freely translating an epigram by the Roman poet Martial; see Hayward (1927)Return to text.

23Schematic depiction of Lang's (1968) "multiple systems" theory of emotion.  Return to text.

24Schematic depiction of LeDoux's (1996) neuropsychological model of fear. Return to text.

25A stimulus item (Card 1) from Murray's (1938) Thematic Apperception Test, adapted from a magazine photograph of the violin virtuoso Yehudi Menuhin (1916-1999) as a child prodigy (Morgan, 2001a, 2001b).  Return to text.

26Murray’s original scheme for coding motive imagery was rather impressionistic (e.g., Murray, 1938) , but over the years McClelland and his colleagues developed a scoring procedure that, properly applied, is as psychometrically rigorous as the best "objective" personality questionnaire (e.g., McAdams, 1980; McClelland, Atkinson, Clark, & Lowell, 1953; Winter, 1973)Return to text.




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