While human consciousness has been discussed throughout the history of written thought, the late 19th century saw a rise of physicalistic reductionism, which, in its more extreme forms, declared "consciousness" and related words taboo in Anglo-American and Soviet science for about seven decades. Thus B.F. Skinner defined his "radical behaviorism" as the complete elimination of mentalistic terms from the vocabulary of psychology --- about two-thirds of the English vocabulary. For about half a century Skinner's influence was immense, and it was extremely difficult for scientists to openly study conscious cognition, voluntary control, personal identity, and similar inferential constructs.
By the 1980s philosophers and scientists started to return to the problem, but now with far better empirical tools than ever before. Philosophers like Daniel Dennett and scientists like Francis Crick have long been strong supporters of empirical studies of subjective experiences.
It has been crucial for scientists to focus on empirically testable questions, rather than purely philosophical or metaphysical ones. This occurs routinely in the history of science when previously untestable questions begin to yield persuasive empirical results. Ambitious longterm outcomes, such as the possible reduction of conscious brain activities to molecular events, are also rarely fruitful at the beginning.
Since the 1980s, a very large scientific literature on consciousness has emerged in biomedicine and psychology, with thousands of published articles on visual awareness, coma and wakefulness, direct brain recordings of binocular rivalry; and much more. PubMed currently shows almost 20,000 articles for the keywords "conscious AND brain." Many studies use "contrastive analysis," empirical comparisons between conscious and unconscious states and contents. This approach has been very fruitful.
There are now dozens of experimental techniques allowing for direct comparisons between conscious and unconscious visual stimuli, using methods like binocular rivalry. Any technique that allows for such direct comparison between (e.g.), unattended words compared to attended ones, may help to clarify our understanding of conscious cognition as well as attention. The empirical harvest since the 1980s has been very large.
Workers in the field are often asked to define "consciousness," but empirical science rarely if ever begins with good definitions. Rather, scientific concepts like "heat," "force" and "momentum" evolve over long periods of time, inductively, not deductively. For example, the thermodynamic definition of "heat" only emerged in the late 19th century. Humans certainly had ideas about "heat" long before that, and scientists from Galileo to Fahrenheit developed increasingly precise ways to measure heat. But without basic 19th century discoveries about the physics of molecular motion and the Kelvin scale, it was useless to demand a theoretical definition of "heat." This very basic point about inductive science is still often misunderstood.
Likewise, demanding a theoretical definition of "consciousness" may not be useful at the beginning of a research program. Instead, we now have a large set of observable operations that tell us when a person is conscious --- though routine measures of waking EEG sometimes fail, as in the case of "locked-in syndrome" and states of intermittent consciousness in coma.
Early empirical measures of new constructs are rarely adequate or complete. We keep improving our measurers whenever possible. For example, direct cortical electrical recording shows a thousand-fold improvement in s/n ratio over raw scalp EEG. (See Table 1)
The traditional and most widely used index of conscious events is "accurate, voluntary report." In the history of sensory perception and psychophysics, accurate report has been immensely fruitful, beginning with Newton's prism experiments and still in wide use today. The scientific study of color perception would have been impossible without accurate, and voluntary reports. In practice, clinical examinations of vision and hearing still rely on accurate, voluntary report, under optimal reporting conditions.
Like other words in natural language, "consciousness" has several meanings. It is used in biomedical science to refer to the state of waking consciousness, as assessed by patient responsiveness to questions, commands, and mild pain, scalp EEG, and the ability to describe current events.
Confusingly, the word "consciousness" is also used to refer to the "dimension of conscious vs. unconscious brain events" --- that is, as an experimental variable that allows us to study brain differences attributable to "consciousness." This second usage is profoundly different from the first, since it implies a measurable dimension of variation. But "consciousness as an empirical variable" is still commonly confused with the waking state, or with subjectivity.
Finally, we use "consciousness of something" to refer to the specific contents of mental life, what we will call "conscious cognitions." Since the domain of conscious contents is vast indeed, it is crucial to distinguish these meanings from each other.
This article is mainly about conscious cognitions. But the state of waking consciousness seems to be necessary for conscious cognitions. While state variables are typically studied separately from content variables, that is only a matter of convenience. A coherent description of conscious brain events must account for both.
In recent decades the relationships between the conscious brain state and its reportable contents has received a great deal of clarification. (See thalamocortical system).
The reportable contents of consciousness include perceptual stimuli; inner speech, reportable dreams and visual imagery; the fleeting present and its fading traces in immediate memory; interoceptive feelings like pleasure, pain, and excitement; the exteroceptive body senses, including touch and pain; reportable emotions; autobiographical events as they are experienced and recalled; clear and immediate intentions, expectations and effortful voluntary control; explicit beliefs about oneself and the world; reportable feelings of knowing (FOKs); novel skills as opposed to overpracticed ones; and concepts that are abstract but still reportable.
This basic list has not changed since Aristotle, and it may indeed be a cultural universal.
In the scientific study of conscious cognitions it is crucial to focus on precise experimental comparisons between contents that are conscious and those that are not. The classical experimental paradigm here is binocular rivalry, where we can now trace the course of two visual content streams in the primate brain, one that is accurately reportable, while the other is not. Numerous studies show that conscious visual streams show more cortical activation, more oscillatory phase-linking, and wider propagation than closely matched unconscious stimuli. Conscious visual stimuli, for example, propagate not only within the visual cortex, but spread to prefrontal and plausibly hippocampal regions for episodic memory coding.
In contrast, experimentally matched unconscious events are not voluntarily reportable, they evoke less neuronal amplitude, show less oscillatory phase-linking, and spread much more locally in cortex.
(However, these points about unconscious sensory input do not apply to other unconscious brain events, notably over-practiced automatisms, cerebellar and striate activities, long-term memories encoded in synaptic connectivity patterns, and the cortical representation of nearby space linked to parietal cortex. Unconscious stimulus processing seems to be different these other types of unreportable brain events.)
A large body of evidence makes use of other experimental paradigms for comparing conscious and unconscious contents, such as visual backward masking, the attentional blink, inattentional blindness, and similar effects in the other senses, like selective listening. Brain measures of these experimental comparisons range from fMRI to PET, intracranial EEG, local field potentials, and even single-neuron recordings. This literature is now very large.
Conscious events can also evoke voluntary actions, notably accurate stimulus reporting. The set of indirect effects of conscious events is very large indeed, and may be an open set --- including sensorimotor control, inner speech, mental problem solving, and emotional reactions. Some downstream events, like amygdala activation, do not present reportable contents, but they often follow from clearly reportable experiences, like an anxiety-provoking images. Emotions in turn trigger widespread autonomic activity, neurohormonal responding, and a large suite of gene expressions.
Recent work using intracranial recording in conscious patients shows that even single temporal lobe neurons can be controlled, on request, using conscious feedback from the target neuron (such as an auditory click when the neuron fires).
These indirect effects of conscious cognitions are important, but this article will focus more narrowly on "the neural correlate of consciousness," i.e., brain activity that corresponds closely to reportable, conscious events.
Ways to study conscious experience
Modern philosophers typically discuss consciousness from a subjective perspective. The philosophical question therefore becomes "what is it like to be a conscious being?"
However, scientists who study conscious and unconscious processes have trouble with such a purely subjectivist approach --- even though they constantly ask people about their personal experiences under specific experimental conditions. Thus a careful scientist might talk about "observer reports" to index conscious experiences, rather than trying to join in the subject's own subjectivity.
As noted above, in the biobehavioral sciences, verifiable reports of conscious experiences have been used for centuries, since the beginnings of sensory psychophysics. We cannot have an eye examination or adjust the color balance on a screen without making use of that extensive body of reliable observations about conscious sensory events.
The hard-and-fast division between philosophy and science is a fairly recent invention, dating to ~1900. Traditional thinkers both in Asia and Europe freely combined what we would call "objective" (public) evidence with "subjective" (first person) experiences. Aristotle and Plato made important observations about conscious cognition --- for example, the distinction between abstract ideas and concrete sensory percepts. In the 17th century Rene Descartes made important empirical discoveries about the optics of oxen eyes and the bilateral organization of the brain, when seen with the naked eye. At the end of the 19th century it was common for major figures like William James to be both empiricists --- in studying hypnosis, for example --- and also to be major philosophers. The Asian tradition of experiential observations and specific mental practices is enormous, and appears to date back to the Indus Valley culture of some 4,500 years ago.
Karl Popper's distinction between empirically falsifiable and non-falsifiable claims continues to be fundamental. Historically, however, before 1900, virtually all philosophers studied empirical as well as non-empirical questions. The notion that philosophy is non-empirical is very recent.
This article will sketch some features of our current scientific understanding of conscious experience, without neglecting subjectivity. To treat consciousness purely "from the outside" would be to ignore the universal human belief that during waking we all experience an endless stream of vivid events from a specific, personal point of view.
Assessing conscious (and unconscious) brain events.
Conscious events can be defined in practice as those brain activities that subjects can report with high accuracy under optimal conditions, such as minimal distraction and minimal time delay. Reportability is a major empirical index that corresponds well with our everyday understanding. Indeed, the words "accurately reportable" can often be used instead of "conscious." However, that would miss something essential‚ the fact that accurate reports refer to a rich Umwelt of experiences that we all claim to have.
Nevertheless, empirical indices evolve over time, better indices of conscious activity are indeed emerging. An obvious example is the "waking EEG," which is different from sleep and drowsiness. Waking EEG has been known since 1929, and provides a primary medical measure of the conscious state, when patients are unable to communicate. Waking EEG is not a perfect measure, and better indices are constantly being developed.
In contrast, unconscious events can be defined as those that are known to exist without the ability report them, such as subliminal activation of cortical regions for color, shape, or object identity.
Thus we have useful empirical indices for both conscious and unconscious brain events even today. As recording methods improve, the set of empirical indices continues to grow.
The need to find comparison conditions.
There are two ways to apply the experimental method to conscious experience. One is to compare conscious events to each other, as we are asked to do in vision and hearing examinations, and in the long history of psychophysics. Conscious event comparisons are standard in fields like sensory perception, recognition memory, mental imagery, short term memory, and the like.
A more recent approach is to compare conscious events with closely matched unconscious ones. This approach dates back several decades, when experimental psychologists and brain researchers discovered convincing evidence for unconscious but "intelligent" brain events, including sensory processing, memory maintenance, automaticity of complex skills, etc.
A simple experiment is to say a word mentally, and then let it fade; for about ten seconds afterwards, it can still be recalled. (The reader is encouraged to try this.) Our ability to retrieve the word even after it has faded from direct experience suggests that an unconscious memory must have been maintained for a little while, with little loss of content. Thus we have both conscious and unconscious phases in working memory, even for a single word. Given that a memory trace continues for a little while even after fading, we can ask, "What is the effect of our being conscious of that word?"
In effect, we have a controlled experiment, allowing us to compare the same word when it is conscious and when it is not. Direct (intracranial) brain recordings show those difference very clearly.
Dozens of contrastive analyses like this can be performed over a range of phenomena. They provide the most directly relevant body of evidence about conscious experience "as such." For example, it is believed that the human cerebellum, which has about the same number of neurons as the cortex, does not support conscious contents. Patients with bilateral injury to the cerebellum are still conscious of roughly the same range of contents as before. Local damage to the cortex, however, does produce a number of very specific deficits in conscious experience, such as cortical color blindness and face blindness --- the inability to recognize a visual pattern as a face, in spite of being able to label eyes, noses, mouths, chins, and so on, with normal accuracy. Specific kinds of cortical blindness can be localized to specific regions of the visual cortex, notably V3/V4 for color perception, and area IT (inferotemporal) for face and object identity. These phenomena have been replicated in other species, notably the Rhesus macaque, which has a strikingly similar visual system to ours.
Science often advances when an apparent constant is realized to be a variable. A famous case is atmospheric pressure, which we intuitively tend to think of as a constant. When the mercury column was invented, the evidence became clear that atmospheric pressure is actually a variable, changing with altitude and great air movements, as in impending storms. Similarly, the study of experimentally matched conscious vs. unconscious brain events has been vital in re-introducing the topic of consciousness to science by allowing us to study both state and content variables.
Notice that such experiments deal directly with subjective phenomenology, as the greater value of the variable of "more vs less" conscious access. All examples used in this article have such unconscious comparison cases. Depending on the specific parameter of consciousness being studied, the variable of interest may have two or more values. It seems unlikely that a complex brain state like consciousness and its absence has only one dimension of variation.
Thus a very large body of solid evidence constrains our hypotheses. Any adequate theory of consciousness must account for the full set of closely matched, experimental contrasts between conscious and unconscious brain events. Theories that aim to do this are by not arbitrary. They are highly constrained by evidence.
Major features of conscious states and contents
1. The raw scalp EEG signature of waking appears “irregular, low-voltage and fast” (12-70 Hz).
However, direct cortical recording improves signal-to noise by a factor of 1,000. Intracranial recording (iEEG) reveals much more detailed, rich and content-specific, signaling among specialized local regions of cortex and thalamus. A useful analogy is between a sports arena emitting random-seeming global crowd noise, compared to thousands of local one-to-one conversations, which are highly regular, event-specific and organized. The more directly cortical activity is observed, the more it resembles coherent conversations between small cortical patches.
Spontaneous conscious mentation is believed to reflect “current goal-driven concerns.” Direct recording of waking activities at the level of neurons and cellular arrays show a very large spatiotemporal signaling vocabulary, linking small cortical regions in a task- and stimulus-specific fashion, from <.1 - 200 Hz. Complex waveforms during waking are believed to reflect a cumulative phase-organized wave hierarchy from slow to fast C-T oscillations. Cross-frequency phase linking is also common. Most cortical sensorimotor areas are organized spatiotopically, so that different cortical regions can interact via labeled-line phase-linking.
The traditional “random” view of waking EEG therefore appears to be an artifact of older, low-resolution, and unanalyzed recording techniques.
2. Conscious visual percepts during the waking state.
A great deal of visual cortical processing is not conscious. Retinal input is conveyed to the optic nerve via ganglion cells, which terminate in the visual thalamus (LGN) without loss of spatial resolution. LGN signals the first cortical projection area, Area V1, with point-to-point accuracy. Long-lasting binocular rivalry is enabled using continuous flash suppression, which allows for single-neuron and multi-unit recording of visual neurons throughout the hierarchy. Neurons responding to the conscious visual stream can be followed independently of those responding to the unconscious stream. For almost three decades, Logothetis and coworkers have systematically traced the two visual streams through the macaque cortex.
While the optic nerve is unidirectional, all higher-level signaling among thalamic and cortical neurons is bidirectional, giving rise to reentrant signaling or adaptive resonance, the typical signaling mode of the cortex and thalamus. From Area V1 the visual signal percolates through more than 40 topographical arrays, emerging as high-level, reportable gestalts near the top of the hierarchy. Recent findings show that reportable visual gestalts emerge in MTL (medial temporal lobe), and are propagated from there to prefrontal regions. Conscious visual contents therefore correspond well to convergent visual “gestalts” in MTL. This is an historic result, built systematically on almost 30 years of cumulative studies.
￼While other sensory systems have not been studied as much as visionl, it seems plausible that auditory, rhinal and somatosensory gestalts may emerge in high level sensory cortex in those modalities. Baars et al (2013) propose that reportable Feelings of Knowing emerge in non-sensory regions of cortex, e.g., the dorsolateral prefrontal cortex for feelings of subjective effort. This is consistent with independent brain imaging evidence.
Thus sensory conscious contents appear to emerge in high-level sensory cortex, while abstract Feelings of Knowing, as in feelings of mental effort or familiarity, may do the same in non-sensory cortex. This evidence is now quite strong in the case of vision, while other conscious modalities need further testing.
3. The most natural unconscious brain state is deep sleep, characterized by widespread delta waves (<2 Hz) in the raw EEG, appearing as regular, high-amplitude, and slow waves. These delta waves reflect coordinated pausing and firing among billions of cortical neurons. Slow-wave sleep serves to consolidate episodic memories acquired in recent conscious periods, and probably has other biological functions as well. The global UP hemicycle of delta sleep allows for a rich mixture of microlevel oscillations and firing for less about 1 sec, while the DOWN hemicycle shows widespread neuronal pausing for the same time. The UP state of delta is therefore thought to resemble a momentary waking period.
The major functional difference between deep sleep and waking may be the regular disruption of waking-like processing during the DOWN hemicycle of delta, every other second. Steriade (2006) has shown that slow oscillations in deep sleep reflect large, traveling waves moving rostrocaudally in the interhemispheric fissure and medial walls of the two hemispheres. Chemically induced unconscious states like general anesthesia are sometimes called “artificial comas,” and may lack the functions of natural slow-wave sleep.
3. REM dreams.
Physiologically, REM dreams resemble the waking state, with eyes closed and occasional large, regular, and stereotyped eye movements. Raw EEG during REM shows “irregular, low-voltage and fast activity,” suggesting waking-like spatiotemporal signaling in the C-T core. Subjects awoken during REM report rich conscious imagery and scenarios, which show narrative discontinuities after perhaps 10 seconds. During lucid (self-conscious) dreaming humans can count to ten using eye movements as a voluntary “end” signal, corresponding to the 10-30 second duration of working memory. Because sensory input is blocked at the level of the thalamus during REM dreams, conscious dream contents appear to reflect purely endogenous cortical activity, both “day residue” from recent waking periods and emotionally driven current concerns. fMRI during dreams shows high metabolic activity in visual and emotional regions of cortex.
4. Anatomical basis of conscious contents.
Conscious contents depends on the thalamocortical complex, with major states switched on and off by brainstem neuromodulation. Regions outside of the C-T complex constantly interact with, but do not directly support reportable conscious contents. Biologically, the C-T complex emerges with mammals (approx. 200 million years ago) and has anatomical homologues in the bird pallium.
￼A great deal of new evidence on the connectivity pattern of the C-T system reveals small-world connectivity, which serves to optimize signal flow. In addition, the C-T system is the most highly parallel-interactive system in the mammalian brain, in marked contrast to the cerebellum, which has similar numbers of neurons but reveals parallel streams of processing. The structural road-map of the C-T system appears to be ideally suited for resolving focal uncertaintie, ambiguities, and decision-points, a major biological challenge that is associated with conscious states and contents. (See Baars et al, 2013). Like the structural map of the C-T system, EEG frequency bands and task-related signal flow follow an inverse frequency law ((1/f) EXP B).
5. Sensory gestalt “broadcasting.” Reportable conscious gestalts spread outside the focus of current conscious contents, as indicated by long-term memory traces, implicit learning, and biofeedback training of autonomic and motor functions. The very fact of accurate reportability implies that executive regions like the prefrontal cortex receive accurate source information from posterior sensory regions. 6. Very wide range of contents. The conscious state has an extraordinary range of contents—sensory perception in the various senses, endogenous imagery, emotional feelings, inner speech, abstract concepts, action-related ideas and Feelings of Knowing such as familiarity, confidence judgments, feelings of effort, and much more.
7. *** TO REVISE *** Informativeness. Conscious contents fade when signals become redundant; a loss of informativeness may also lead to a loss of conscious access. Attentional selection also shows a strong preference for more informative conscious stimuli. Updating.
8. The rapidly adaptive and fleeting nature of conscious scenes.
9. Immediate experience of the sensory past may last a few seconds, and our fleeting cognitive present is surely less than half a minute. In contrast, vast bodies of unconscious knowledge reside in long-term memory.
10. Internal consistency of conscious contents. Conscious contents are marked by a consistency constraint. For example, while multiple meanings of most words are active for a brief time after presentation, only one becomes conscious at any moment. In general, of two mutually inconsistent stimuli presented simultaneously, only one can become conscious.
11. Limited capacity and seriality. The capacity of consciousness at any given moment seems limited to one consistent scene (see above). The flow of such scenes is serial, in contrast with the massive parallelism of the brain as observed directly.
12. Multiple levels of binding (integration). Sensory cortex is functionally specialized, such that different cortical areas respond to different features such as sense modality, shape, color, spatial location and object motion. One classic question is how these functionally separate regions coordinate their activities to generate the reportable gestalts of everyday conscious perception.
13. Multiple problem-solving funcitons; Uncertainty reduction.
￼14. Implicit self-attribution. Conscious experiences are always attributed to an experiencing but implicit self, the ‘‘observing self’’ as James called it. Self-functions appear to be associated with several brain regions, prominently orbitofrontal cortex in humans. It is important that most of this “observing ego system” does not itself enable accurate reports of its activities. The observing I therefore seems to be provide an implicit framework within which conscious gestalts are defined, but which is not conscious in and of itself. From this point of view, the “I” system specifies a frame or a viewpoint, with a body-centered spatial surround, which works in coordination with external object-centered coordinates (allocentric) needed to understand the spatial context of conscious objects. Both hippocampal/entorhinal and parietal regions are known to have such egocentric and allocentric spatial maps.
15. Accurate reportability. Conscious contents are reportable by a wide range of voluntary responses, often with very high accuracy. The conventional operational index of consciousness is based on accurate reportability. Notice that humans are also marked by a lush imaginative life, as shown by way of legends, other-worldly beings, dream contents, and much more. Thus our brains have dual specializations --- we can be extremely accurate (which is clearly functional in dealing with dangers and opportunities in the real world) and we are also very imaginative. This is not merely an artefact of high technology.
16. Subjectivity. Consciousness is marked by a private flow of events available only to the reporting subject. Reportability applies to the classical senses, but not to the vestibular (balance) sense, for example, nor to parietal control of reaching, online syntactic analysis of verbal input, and much more. The brain differences between conscious and unconscious functions is not currently understood.
17. Focus-fringe structure. While consciousness tends to be thought of in terms of focal, clearly articulated sets of contents, Feelings of Knowing (FOKs), sometimes called “fringe feelings,” are extremely common and important. A vast number of complex and accurate knowledge sources present as FOK’s, including the famous tip-of-the-tongue state, which involves a great deal of semantic and linguistic knowledge. William James rightly pointed out the great importance of FOK’s in mental life.
18. Facilitation of learning. There is very little evidence for long-term learning of unconscious input. In contrast, the evidence of learning of conscious episodes is overwhelming. Even implicit learning requires conscious attention to the stimuli from which implicit regularities are (unconsciously) inferred.
19. Experienced stability of contents. Conscious contents are impressively stable, given the variability of sensory events they incorporate. Even abstract contents such as beliefs, concepts, and the motivational self are remarkably stable over the adult lifetime.
20. Allocentricity. (“object” centeredness). Neural representations of external objects make use of diverse frames of reference. Conscious scenes, generally speaking, have allocentric character, though they are shaped by egocentric and many other unconscious frameworks.
21. Conscious knowing and decision making. Consciousness is useful for knowing the world around us, as well as for knowing some of our own internal processes, such as interoceptive feelings represented in the anterior insular cortex. Conscious goal states involve insular, premotor and supplementary motor cortex, and enabled prepare set for voluntary decision making.
It is difficult to prove the complete absence of consciousness in state studies. Sleep can vary in arousability from moment to moment, much like vegetative (comatose) states and even general anesthesia. Some mentation is reported even when subjects are woken from slow-wave sleep, and some waking-like functions can be preserved in brain damage patients in "behavioral coma" --- though not in true brain coma. One class of supposedly comatose patients are known to be awake but paralyzed, a condition that is called "locked-in" syndrome. Some of these patients have been rescued by training them to use voluntary eye movements and voluntary eye fixations on the letters of a computer keyboard, to allow them to communicate quite normally. Since any voluntary response can be used to report conscious experiences, voluntary eye movements and fixations are as good as finger pointing or verbal reports.
It is not known whether the variable of conscious vs. unconscious brain states has a true zero point. Relatively unconscious slow-wave sleep has now been shown to allow for reliable reports of mentation. Surprising awakenings have also been reported from general anesthesia and long-term coma. Some scientists have used very deep general anesthesia in experimental animals to define a ground state of brain functioning. For most purposes, however, a zero point of conscious state variation is not needed. There is no question that deep sleep is less conscious than full, responsive waking.
Deep sleep is characterized by massive, synchronized delta waves, <2 Hz, in the cortex and thalamus. Since the trough of the delta wave involves widespread pausing of neuronal firing, it is thought to be close to a zero point, while the peak of delta allows for a wide range of faster oscillations and normal-seeming neuronal firing. Even deep sleep may therefore be an intermittently conscious state, during the ~1-2 Hz peak of the recurrent delta wave.
It is well-known, of course, that physiologically, deep sleep is a very active state, one that is needed for consolidation of daytime (waking) experiential memory traces via hippocampal-neocortical theta-gamma signaling. We do not know the full set of psychological and biological functions of deep sleep, but more than 200 types of gene expression are known to correlate with the sleep-waking cycle. A low level of consciousness during deep sleep therefore does not imply the absence of very active, biologically fundamental brain activities.
Fringe conscious events
What is fringe consciousness? Imagine that our focal conscious experiences are surrounded by a vaguer "penumbra," to represent what William James called "fringe consciousness." If we take focal consciousness to include immediate, detailed experiences, the "fringe" would cover those cases in which we have reliable access to information without being able to experience it explicitly in detail. Dr. Bruce Mangan has helped revive a philosophical tradition about the fringe, including such experiences as feelings of knowing, of familiarity, beauty and goodness, of something not quite fitting, or a sudden profound feeling of rightness. A surprising amount of our mental life is occupied with fringe events, which may be experienced as fuzzy or vague, but which have properties suggesting that something very precise is going on.
Take the “feeling of knowing” that comes when we ask a question like "What is the name of the flying reptiles of the dinosaur age?" Most of us have trouble finding the answer right away, but we know that we know it, and rightly so. Feelings of knowing have been studied extensively, and the evidence indicates that (1) they are quite accurate most of the time; (2) they receive high confidence ratings; but (3) they do not involve detailed, structured experiences, unlike the sight of a coffee cup, where we can talk about shape, color, shading, texture, and many other details.
We have "feelings of knowing" about items in working memory that are not currently conscious. Moreover, we seem to have feelings of knowing about things that are readily available to consciousness, though they are not conscious at the moment --- our ability to retrieve known words, our mood, our ability to act and control some mental functions, our basic knowledge about friends, family and ourselves, and much more.
Fringe conscious experiences can be defined empirically, just as conscious and unconscious events can be. One can simply define them as "reportable experiences that are verifiable, and which are reported with high certainty, but with little descriptive detail." In the case of a visual coffee cup, we have both certainty and the ability to describe the components of the experience in great detail. In the case of feelings of familiarity, we do not necessarily have that. Thus "fringe conscious events" constitute a very large category of mental events that is as important as conscious and unconscious events.
Unusual conscious experiences
Different types of consciousness:
- primary (perceptual) versus higher-order (conceptual) consciousness
- Access versus phenomenal consciousness
- hard problem versus easy problem
- explicit versus implicit processes