Scientific Understanding of Consciousness
Consciousness as an Emergent Property of Thalamocortical Activity

Unconscious Cognitive Processes



Science 18 September 1987: Vol. 237. no. 4821, pp. 1445 1452

The Cognitive Unconscious

John F. Kihlstrom

Professor in the Department of Psychology, University of Arizona, Tucson, AZ


Contemporary research in cognitive psychology reveals the impact of nonconscious mental structures and processes on the individual's conscious experience, thought, and action. Research on perceptual-cognitive and motoric skills indicates that they are automatized through experience, and thus rendered unconscious. In addition, research on subliminal perception, implicit memory, and hypnosis indicates that events can affect mental functions even though they cannot be consciously perceived or remembered. These findings suggest a tipartite division of the cognitve unconscious into truly unconscious mental processes operating on knowledge structures that may themselves be preconscious or subconscious.

Declarative knowledge can be classified as either episodic or semantic. Episodic memory is autobiographical in character, and contains more or less explicit reference to the self as the agent or experiencer of some event, and the unique environmental and organismic context in which that event occurred. Semantic memory is the "mental lexicon" of abstract knowledge, stored without reference to the circumstances in which it was acquired.

Automatic Processes

A good deal of mental activity is unconscious in the sense of being inaccessible to phenomenal awareness under any circumstances. In conversational speech, for example, the listener is aware of the meanings of the words uttered by the speaker but not of the phonological and linguistic principles by which the meaning of the speaker's utterance is decoded. Similarly, during perception the viewer may be aware of two objects in the external environment but not of the mental calculations performed to determine that one is closer or larger than the other. Although we have conscious access to the results of these mental processes, we have no conscious access to their operations.

Unconscious procedural knowledge of this sort appears to be innate. In fact, Fodor has proposed that the mind consists of a number of innate, domain-specific cognitive modules controlling such activities as language and visual perception, hardwired in the nervous system and operating outside of conscious awareness and voluntary control. However, other cognitive procedures appear to be acquired through experience. In the case of skill learning, the steps involved become unconscious by virtue of practice, as indicated by the inability of many musicians, athletes, and typists to describe their skills to others, and by the fact that conscious attention to them actually interferes with their performance. In other words, skills that are not innate may become routinized through practice, and their operations thereby rendered unconscious. In this way, both innate and acquired cognitive procedures may be unconscious.

Unconscious procedural knowledge has also been described as automatic as opposed to controlled or effortful. Automatic processes are so named because they are inevitably engaged by the presentation of specific stimulus inputs, regardless of any intention on the part of the subject. In addition, automatic processes consume little or no attentional resources. It is a fundamental premise of cognitive psychology that the amount of attention that can be allocated to various activities is limited, producing a bottleneck in information processing.

Nevertheless, automatic processing may have some negative consequences as well. Effective memory depends to a great extent on the amount and type of cognitive activity devoted to the event at the time of perception, and some automatized processes--however well suited they are for other tasks--may not encourage good encodings.

The fact that automatized processes consume little or no attentional capacity has important consequences for consciousness. In the first place, of course, automatic processes are themselves unconscious, in that the person has no introspective access to their principles of operation-or even the fact that they are in operation at all. Thus, fluent speakers of English agree that the phrase 'the big red barn" is grammatically better than the phrase 'the red big barn," even though they are unable to articulate the underlying syntactical rule that guides such decisions. Similarly, in the social domain, speakers may like one face more than another, while being unable to say exactly why they have that preference. A large number of social judgments and inferences, especially those guiding first impressions, appear to be mediated by such unconscious processes.

Experiments on automaticity are important because they indicate that a great deal of complex cognitive activity can go on outside of conscious awareness, provided that the skills, rules, and strategies required by the task have been automatized. They expand the scope of unconscious preattentive processes, which were previously limited to elementary perceptual analyses of the physical features of environmental stimuli. Now it is clear that there are circumstances under which the meanings and implications of events can be unconsciously analyzed as well. Thus, people may reach conclusions about events -- for example, their emotional valence -- and act on these judgments without being able to articulate the reasoning by which they were reached. This does not mean that cognitive activity is not involved in such judgments and inferences; it only means that the cognitive activity, being automatized, is unconscious and thus unavailable to introspective awareness.

Subliminal Perception

Subliminal perception refers to the possibility that stimuli too weak to be consciously detected nonetheless have an impact on perceptual and cognitive functioning. Subliminal perception is often studied by presenting stimuli for intervals (for example, less than 5 milliseconds) that are too brief to be consciously perceived. A .number of investigators have found that such stimuli reappear in subsequent dreams (the Poetzel phenomenon) and otherwise affect the person's performance on some experimental task.

For obvious reasons, subliminal perception is of considerable interest to the advertising community; it has also been of considerable interest to psychoanalysts and others who believe that people defend against potentially threatening percepts, memories, ideas, and impulses by excluding them from awareness.

Research studies indicate that preconscious processing affects emotional as well as semantic judgments. Many of these demonstrations rely on the mere exposure effect, which refers to the fact that repeated presentation of a previously unfamiliar stimulus tends to increase its attractiveness (contrary to folklore, familiarity does not necessarily breed contempt). Thus, by virtue of prior preconscious presentation, subjects come to prefer stimuli that they do not recognize as familiar.

It does seem that preconscious declarative knowledge is subject to analysis by unconscious procedural knowledge. Such information processing activity would be nonconscious in a double sense: neither the stimuli themselves, nor the cognitive processes that operate on them, are accessible to phenomenal awareness. Such doubly nonconscious processes nevertheless exert an important impact on social interaction. Through the operation of routinized procedures for social judgment, for example, we may form impressions of people without any conscious awareness of the perceptual-cognitive basis for them.

Results such as these are important for cognitive theory because they indicate that a great deal of information processing takes place outside of working memory. Apparently, perceptual processing automatically activates preexisting semantic memory structures corresponding to the features of the stimulus event, as well as related nodes by virtue of spreading activation. If some of these nodes correspond to the goals and conditions of various production systems, certain procedures will be executed as well. However, none of this requires the involvement of working memory. Thus, in contrast to the implications of the classic model for human information processing, a great deal of complex cognitive activity can be devoted to stimuli that are themselves outside of phenomenal awareness.

Implicit Memory

Because preconscious processing appears to be mediated by the activation of relevant mental representations already stored in memory, the question is raised whether analogous effects may be observed in memory itself. That is, just as there are palpable effects on experience, thought, and action of stimuli that cannot be consciously perceived, so there may be similar effects of events that cannot be consciously remembered.

Some of the most dramatic instances of nonconscious memory appear in cases of the amnesic syndrome (sometimes called Korsakoff's syndrome), which results from bilateral damage to the medial temporal lobe (including the hippocampus) and diencephalon (including the mammiliary bodies) of the brain. Patients suffering from this disorder (which may reflect a number of different etiologies, including chronic alcoholism) manifest a gross anterograde amnesia, meaning that they cannot remember events that occurred since the onset of the brain damage; other intellectual functions remain relatively intact.

Hypnotic Alterations of Consciousness

Hypnosis is a social interaction in which one person, the subject, responds to suggestions offered by another person, the hypnotist, for experiences involving alterations in perception, memory, and action. One common aspect of these experiences is an alteration in phenomenal awareness, but the changes in consciousness are not precisely the same as those seen in automaticity, subliminal perception, and implicit memory.

In hypnotic analgesia, hypnotized subjects may fail to experience discomfort from a normally painful stimulus. A number of findings indicate that the pain stimulus has been adequately registered by the sensory-perceptual system. The success of the technique indicates that analgesic subjects may be unaware of stimuli that have been thoroughly processed by the sensory-perceptual system.

Within the domain of memory, similar anomalies of awareness may be noted in posthypnotic amnesia. Following appropriate suggestions, subjects may fail to remember the events and experiences that transpired while they were hypnotized. However, the critical memories may be recovered after administration of a prearranged signal to cancel the amnesia suggestion. This property of reversibility clearly shows that posthypnotic amnesia reflects a disruption of memory retrieval, rather than a failure of encoding or loss from storage.

Unconscious, Preconscious, and Subconscious

The results of these and other experiments, conducted in a wide variety of circumstances and with many different types of subjects, lead to a provisional taxonomy of nonconscious mental structures and processes constituting the domain of the cognitive unconscious. One thing is now clear: consciousness is not to be identified with any particular perceptual-cognitive functions such as discriminative response to stimulation, perception, memory, or the higher mental processes involved in judgment or problem-solving. All of these functions can take place outside of phenomenal awareness. Rather, consciousness is an experiential quality that may accompany any of these functions. The fact of conscious awareness may have particular consequences for psychological function it seems necessary for voluntary control, for example, as well as for communicating one's mental states to others. But it is not necessary for complex psychological functioning.

More specifically, there are, within the domain of procedural knowledge, a number of complex processes that are inaccessible to introspection in principle under any circumstances. By virtue of routinization (or perhaps because they are innate), such procedures operate on declarative knowledge without either conscious intent or conscious awareness, in order to construct the person's ongoing experience, thought, and action. These mental processes, which can be known only indirectly through inference, may be described as unconscious.

It is now clear that procedural knowledge can interact with, and utilize, declarative knowledge that is not itself accessible to conscious awareness. The phenomena of subliminal perception and implicit memory, then, suggest a category of preconscious declarative knowledge structures. Unlike automatized procedural knowledge, these percepts and memories would be available to awareness under ordinary circumstances. Although activated to some degree by current or prior perceptual inputs, and thus able to influence ongoing experience, thought, and action, they do not cross the threshold required for representation in working memory, and thus for conscious awareness.

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