Subliminal

since the time of the Greeks.¹ Among the most influential of the thinkers delving into the psychology of consciousness was the eighteenth-century German philosopher Immanuel Kant. During his time, psychology was not an independent subject but merely a catchall category for what philosophers and physiologists discussed when they speculated about the mind.² Their laws concerning human thought processes were not scientific laws but philosophical pronouncements. Since these thinkers required little empirical basis for their theorizing, each one was free to favor his own purely speculative theory over his rival’s purely speculative theory. Kant’s theory was that we actively construct a picture of the world rather than merely documenting objective events, that our perceptions are not based just on what exists but, rather, are somehow created—and constrained—by the general features of the mind. That belief was surprisingly near the modern perspective, though today scholars generally take a more expansive view than Kant’s of the mind’s general features, especially with regard to biases arising from our desires, needs, beliefs, and past experiences. Today we believe that when you look at your mother-in-law, the image you see is based not only on her optical qualities but also on what is going on in your head—for example, your thoughts about her bizarre child-rearing practices or whether it was a good idea to agree to live next door.

Kant felt that empirical psychology could not become a science because you cannot weigh or otherwise measure the events that occur in your brain. In the nineteenth century, however, scientists took a stab at it. One of the first practitioners was the physiologist E. H. Weber, the man who, in 1834, performed the simple experiment on the sense of touch that involved placing a small reference weight at a spot on his subjects’ skin, then asking them to judge whether a second weight was heavier or lighter than the first.³ The interesting thing Weber discovered was that the smallest difference a person could detect was proportional to the magnitude of the reference weight. For example, if you were just barely able to sense that a six-gram weight was heavier than a reference object that weighed five grams, one gram would be the smallest detectible difference. But if the reference weight were ten times heavier, the smallest difference you’d be able to detect would be ten times as great—in this case, ten grams. This doesn’t sound like an earth-shattering result, but it was crucial to the development of psychology because it made a point: through experimentation one can uncover mathematical and scientific laws of mental processing.

In 1879 another German psychologist, Wilhelm Wundt, petitioned the Royal Saxon Ministry of Education for money to start the world’s first psychology laboratory.⁴ Though his request was denied, he established the laboratory anyway, in a small classroom he had already been using, informally, since 1875. That same year, a Harvard MD and professor named William James, who had taught Comparative Anatomy and Physiology, started teaching a new course called The Relations Between Physiology and Psychology. He also set up an informal psychology laboratory in two basement rooms of Lawrence Hall. In 1891 it attained official status as the Harvard Psychological Laboratory. In recognition of their pathbreaking efforts, a Berlin newspaper referred to Wundt as “the psychological Pope of the Old World” and James as “the psychological Pope of the New World.”⁵ It was through their experimental work, and that of others inspired by Weber, that psychology was finally put on a scientific footing. The field that emerged was called the “New Psychology.” For a while, it was the hottest field in science.⁶

The pioneers of the New Psychology each had his own views about the function and importance of the unconscious. The British physiologist and psychologist William Carpenter was one of the most prescient. In his 1874 book Principles of Mental Physiology, he wrote that “two distinct trains of Mental action are carried on simultaneously, one consciously, the other unconsciously,” and that the more thoroughly we examine the mechanisms of the mind, the clearer it becomes “that not only an automatic, but an unconscious action enters largely into all its processes.”⁷ This was a profound insight, one we continue to build on to this day.

Despite all the provocative ideas brewing in European intellectual circles after the publication of Carpenter’s book, the next big step in understanding the brain along the lines of Carpenter’s two-trains concept came from across the ocean, from the American philosopher and scientist Charles Sanders Peirce—the man who did the studies of the mind’s ability to detect what should have been undetectable differences in weight and brightness. A friend of William James’s at Harvard, Peirce had founded the philosophical doctrine of pragmatism (though it was James who elaborated on the idea and made it famous). The name was inspired by the belief that philosophical ideas or theories should be viewed as instruments, not absolute truths, and their validity judged by their practical consequences in our lives.

Peirce had been a child prodigy.⁸ He wrote a history of chemistry when he was eleven. He had his own laboratory when he was twelve. At thirteen, he studied formal logic from his older brother’s textbook. He could write with both hands and enjoyed inventing card tricks. He was also, in later life, a regular user of opium, which was prescribed to relieve a painful neurological disorder. Still, he managed to turn out twelve thousand printed pages of published works, on topics ranging from the physical sciences to the social sciences. His discovery of the fact that the unconscious mind has knowledge unknown to the conscious mind—which had its unlikely origin in the incident in which he was able to form an accurate hunch about the identity of the man who stole his gold watch—was the forerunner of many other such experiments. The process of arriving seemingly by chance at a correct answer you aren’t aware of knowing is now used in what is called a “forced choice” experiment, which has become a standard tool in probing the unconscious mind. Although Freud is the cultural hero associated with popularizing the unconscious, it is really to pioneers like Wundt, Carpenter, Peirce, Jastrow, and William James that we can trace the roots of modern scientific methodology and thought about the unconscious mind.

TODAY WE KNOW that Carpenter’s “two distinct trains of Mental action” are actually more like two entire railway systems. To update Carpenter’s metaphor, we would say that the conscious and unconscious railways each comprise a myriad of densely interconnected lines, and that the two systems are also connected to each other at various points. The human mental system is thus far more complex than Carpenter’s original picture, but we’re making progress in deciphering its map of routes and stations.

What has become abundantly clear is that within this two-tier system, it is the unconscious tier that is the more fundamental. It developed early in our evolution, to deal with the basic necessities of function and survival, sensing and safely responding to the external world. It is the standard infrastructure in all vertebrate brains, while the conscious can be considered an optional feature. In fact, while most nonhuman species of animals can and do survive with little or no capacity for conscious symbolic thought, no animal can exist without an unconscious.

According to a textbook on human physiology, the human sensory system sends the brain about eleven million bits of information each second.⁹ However, anyone who has ever taken care of a few children who are all trying to talk to you at once can testify that your conscious mind cannot process anywhere near that amount. The actual amount of information we can handle has been estimated to be somewhere between sixteen and fifty bits per second. So if your conscious mind were left to process all that incoming information, your brain would freeze like an overtaxed computer. Also, though we don’t realize it, we are making many decisions each second. Should I spit out my mouthful of food because I detect a strange odor? How shall I adjust my muscles so that I remain standing and don’t tip over? What is the meaning of the words that person across the table from me is uttering? And what kind of person is he, anyway?

Evolution has provided us with an unconscious mind because our unconscious is what allows us to survive in a world requiring such massive information intake and processing. Our sensory perception, our memory recall, our everyday decisions, judgments, and activities all seem effortless—but that is only because the effort they demand is expended mainly in parts of the brain that function outside awareness.

Take speech. Most people who read the sentence “The cooking teacher said the children made good snacks” instantly understand a certain meaning for the word “made.” But if you read, “The cannibal said the children made good snacks,” you automatically interpret the word “made” in a more alarming sense. Though we think that making these distinctions is easy, the difficulty in making sense of even simple speech is well appreciated by computer scientists who struggle to create machines that can respond to natural language. Their frustration is illustrated by a possibly apocryphal story of the early computer that was given the task of translating the homily “The spirit is willing but the flesh is weak” into Russian and then back into English. According to the story, it came out: “The vodka is strong but the meat is rotten.” Luckily, our unconscious does a far better job, and handles language, sense perception, and a teeming multitude of other tasks with great speed and accuracy, leaving our deliberative conscious mind time to focus on more important things, like complaining to the person who programmed the translation software. Some scientists estimate that we are conscious of only about 5 percent of our cognitive