The contents of consciousness include the perceptual world; inner speech and visual imagery; the fleeting present and its fading traces in immediate memory; bodily feelings like pleasure, pain, and excitement; surges of emotional feeling; autobiographical events when they are recalled; clear and immediate intentions, expectations and actions; explicit beliefs about oneself and the world; and concepts that are abstract but focal.
Ways to study conscious experience
Modern philosophers typically discuss consciousness from a subjective perspective. The classical question therefore becomes "what is it like to be a conscious being?" However, modern scientists who study conscious and unconscious processes have trouble with such a purely subjectivist approach, but constantly ask people about their experiences in specific experimental conditions. Thus a careful scientist might talk about "observer reports" to index conscious experiences, rather than leap in to the subject's own subjectivity. In the biobehavioral sciences, verifiable reports of conscious experiences have been used for at least two centuries, since the beginnings of psychophysics. We cannot have an ordinary eye examination or even adjust the color balance on a computer screen without making use of that long empirical tradition of reliable observations about conscious perception.
The hard-and-fast division between philosophy and science is a fairly recent invention, dating to the years before 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 human consciousness --- for example, the distinction between abstract ideas and concrete percepts goes back at least to that time. In the 17th century, Rene Descartes made important empirical discoveries about the eyes of oxen and the brains of sheep. 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 be considered to be major philosophers. The hard division between philosophy and science is largely a 20th century invention, and it appears to be fading somewhat in recent years.
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 what human beings universally find most compelling about consciousness, that it enables vast stream of vivid internal events, experienced from a specific and personal point of view. (Since we cannot cover the vast literature on the philosophy of mind, interested readers should consult it directly. See recommended readings, below).
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 minimal distraction and time delay. Reportability is a very useful empirical index, and it corresponds well with our everyday understanding of conscious experiences. Indeed, the words "accurately reportable" could be used instead of "conscious". However, that would miss out something essential‚ namely the fact that accurate reports are about experiences that all intact humans claim to have.
Nevertheless, empirical indices evolve over time in the sciences, and no doubt we will discover better brain indices of conscious activity over time. An obvious example is the "waking EEG," which is different from sleep or dreaming EEG. It has been known since 1929, and provides an excellent measure of conscious activity in medical conditions in which patients cannot communicate. While there are cases where ordinary EEG fails as an index of consciousness, in the great majority of human beings it is a very useful index. Better brain indices are constantly being tested.
In contrast to the empirical index of conscious events, unconscious events can be defined as those that are known to exist without the ability report them accurately, such as subliminal activation of cortical regions for color, shape, or object identity in the appropriate parts of the brain. Thus we have quite adequate empirical indices for both conscious and unconscious brain activities even today.
The need to find comparison conditions for conscious events.
There are two ways to apply the experimental method to the topic of conscious experience. One is to compare conscious events to each other: This has been standard in numerous experiments, especially in fields like perception, psychophysics, memory, mental imagery, inner speech, and the like. All of our understanding of vision, audition, and the other senses has evolved from such experimental methods.
Take a simple experiment. We can 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 a few times.) Our ability to retrieve the word with accuracy 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 elements in our working memory. Given that a word trace still exists for a little while even after fading from consciousness, we can ask, "What is the effect of our being conscious of a word?" In effect, we have a controlled experiment, allowing us to compare the same word when it is conscious and when it is not.
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 generally thought that the human cerebellum, which contains about the same number of neurons as the cortex, does not support conscious contents. People with a damaged cerebellum are still conscious of roughly the same range of contents as healthy people. Local damage to the cortex, however, does produce a number of very specific deficits in conscious experience, such as face blindness, the inability to recognize a visual pattern as a face, in spite of being able to label colors, noses, mouths, chins, and so on, with normal accuracy.
A number of historic breakthroughs in science have emerged from the realization that some previously assumed constant, like atmospheric pressure or gravity, was actually a variable. We can make use of this classic scientific strategy to explore consciousness. The study of selective conscious (but not unconscious) brain deficits has been important in re-introducing consciousness to science as an empirically testable subject.
Notice that such contrastive experiments deal directly with personal phenomenology, as anyone can demonstrate in their own experience. Repeating a word inwardly is one such case. Seeing a face "as a face" is another one. All examples in this article involve highly reliable personal experiences. Any adequate theory of consciousness must account for the entire set of such contrasts between matched conscious and unconscious brain activities, which is a very large set. The topic of conscious experience is therefore highly constrained by evidence.
Conscious states vs. specific conscious experiences.
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 from slow-wave sleep, and some waking-like functions can be preserved in rare brain damage patients who seem behaviorally unconscious. For most purposes, however, an absolute, stable zero point of consciousness is not needed. There is no question that deep sleep is much less conscious than full, responsive waking.
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