Determining how this involuntary feeling of knowing happens takes us into the enormously complicated details of neurobiology. To simplify them for this discussion, let me borrow a term, "hidden layer," from the artificial intelligence community.
By mimicking the way the brain processes information, A.I. scientists have been able to build artificial neural networks (ANNs) that can play chess and poker, read faces, recognize speech and recommend books at Amazon.com. While standard computer programs work line by line, yes or no, all eventualities programmed in advance, the ANN takes an entirely different approach. The ANN is based upon mathematical programs that are initially devoid of any specific values. The programmers only provide the equations; incoming information determines how connections are formed and how strong each connection will be in relationship to all other connections. There is no predictable solution to a problem -- rather, as one connection changes, so do all the others. These shifting interrelationships are the basis for "learning."
With an ANN, the hidden layer is conceptually located within the interrelationships between all the incoming information and the mathematical code used to process it. In the human brain, the hidden layer doesn't exist as a discrete interface or specific anatomic structure; rather, it resides within the connections between all neurons involved in any neural network. A network can be relatively localized or widely distributed throughout the brain. Proust's taste of a madeleine triggered a memory that involved visual, auditory, olfactory and gustatory cortices -- the multisensory cortical representations of a complex memory. With a sufficiently sensitive fMRI scan, we would see all these areas lighting up when Proust contemplated the madeleine.
The hidden layer thus offers a powerful metaphor for the way the brain processes information. It is in the hidden layer that all elements of biology (from genetic predispositions to neurotransmitter variations and fluctuations) and all past experience, whether remembered or long forgotten, affect the processing of incoming information. It is the interface between incoming sensory data and a final perception, the anatomic crossroad where nature and nurture intersect. It is why your red is not my red, your idea of beauty isn't mine, why eyewitnesses offer differing accounts of an accident or why we don't all put our money on the same roulette number.
The powerful feeling of knowing arises out of the hidden layer's unconscious calculation of correctness, be it recognizing a face or believing an idea is right. The greater the likelihood of correctness, as determined by your unconscious, the stronger the sense of certainty.
In his bestselling "Blink," New Yorker staff writer Malcolm Gladwell describes gut feelings as "perfectly rational," as "thinking that moves a little faster and operates a little more mysteriously" than conscious thought. But he's flying in the face of present-day understanding of brain behavior. Gut feelings and intuitions, the Eureka moment and our sense of conviction, represent the conscious experiences of unconsciously derived feelings.
Look at the feeling of knowing in the light of evolution. It explains how we learn. Compare it with the body's various sensory systems. It is through sight and sound that we are in contact with the world around us. Similarly, we have extensive sensory functions for assessing our interior milieu. When our body needs food, we feel hunger. When we are dehydrated and require water, we feel thirsty. If we have sensory systems to connect us with the outside world, and sensory systems to notify us of our internal bodily needs, it seems reasonable that we would also have a sensory system to tell us what our minds are doing.
To be aware of thinking, we need a sensation that tells us that we are thinking. To reward learning, we need feelings of being on the right track, or of being correct. And there must be similar feelings to reward and encourage the as-yet unproven thoughts -- the idle speculations and musings that will become useful new ideas.
To be an effective, powerful reward, the feeling of conviction must feel like a conscious and deliberate conclusion. As a result, the brain has developed a constellation of mental sensations that feel like thoughts but aren't. These involuntary and uncontrollable feelings are the mind's sensations; as sensations they are subject to a wide variety of perceptual illusions common to all sensory systems. Understanding this couldn't be more important to our sense of ourselves and the world around us.
It's not easy, of course, but somehow we must incorporate what neuroscience is telling us about the limits of knowing into our everyday lives. We must accept that how we think isn't entirely within our control. Perhaps the easiest solution would be to substitute the word "believe" for "know." A physician faced with an unsubstantiated gut feeling might say, "I believe there's an effect despite the lack of evidence," not, "I'm sure there's an effect." And yes, scientists would be better served by saying, "I believe that evolution is correct because of the overwhelming evidence."
I realize that this last sentence runs against the grain of those who have fought the hardest to establish science as the method for determining the facts of the external world. It is particularly loathsome when you feel that you are playing into the hands of religious fanatics, medical quacks and word-twisting politicians. But in pointing out the biological limits of reason, including scientific thought, I'm not making the case that all ideas are equal or that scientific method is mere illusion. My purpose is not to destroy the foundations of science, but only to point out the inherent limitations of the questions that science asks and the answers it provides.
Substituting believe for know doesn't negate scientific knowledge; it only shifts a hard-earned fact from being unequivocal to being highly likely. Saying that evolution is extremely likely rather than absolutely certain doesn't reduce the strength of the argument, and at the same time it serves a more fundamental purpose. Hearing myself saying "I believe" where formerly I would have said "I know" serves as a constant reminder of the limits of knowledge and objectivity. At the same time as I am forced to consider the possibility that contrary opinions might have a grain of truth, I am provided with the perfect rebuttal for those who claim that they "know that they are right." It is in the leap from 99.99999 percent likely to 100 percent guaranteed that we give up tolerance for conflicting opinions, and provide the basis for the fundamentalist's claim to pure and certain knowledge.
Next page: We must tolerate the unpleasantness of uncertainty