Subliminal: how your unconscious mind rules your behavior - Leonard Mlodinow 2013


These subliminal aspects of everything that happens to us may seem to play very little part in our daily lives. But they are the almost invisible roots of our conscious thoughts. —CARL JUNG

IN JUNE 1879, the American philosopher and scientist Charles Sanders Peirce was on a steamship journey from Boston to New York when his gold watch was stolen from his stateroom.1 Peirce reported the theft and insisted that each member of the ship’s crew line up on deck. He interviewed them all, but got nowhere. Then, after a short walk, he did something odd. He decided to guess who the perpetrator was, even though he had nothing to base his suspicions on, like a poker player going all in with a pair of deuces. As soon as Peirce made his guess, he found himself convinced that he had fingered the right man. “I made a little loop in my walk,” he would later write, “which had not taken a minute, and as I turned toward them, all shadow of doubt had vanished.”2

Peirce confidently approached his suspect, but the man called his bluff and denied the accusation. With no evidence or logical reason to back his claim, there was nothing Peirce could do—until the ship docked. When it did, Peirce immediately took a cab to the local Pinkerton office and hired a detective to investigate. The detective found Peirce’s watch at a pawnshop the next day. Peirce asked the proprietor to describe the man who’d pawned it. According to Peirce, the pawnbroker described the suspect “so graphically that no doubt was possible that it had been my man.” Peirce wondered how he had guessed the identity of the thief. He concluded that some kind of instinctual perception had guided him, something operating beneath the level of his conscious mind.

If mere speculation were the end of the story, a scientist would consider Peirce’s explanation about as convincing as someone saying, “A little birdie told me.” But five years later Peirce found a way to translate his ideas about unconscious perception into a laboratory experiment by adapting a procedure that had first been carried out by the physiologist E. H. Weber in 1834. Weber had placed small weights of varying degrees of heaviness, one at a time, at a spot on a subject’s skin, in order to determine the minimum weight difference that could be detected by the subject.3 In the experiment performed by Peirce and his prize student, Joseph Jastrow, the subjects of the study were given weights whose difference was just below that minimum detectable threshold (those subjects were actually Peirce and Jastrow themselves, with Jastrow experimenting on Peirce, and Peirce on Jastrow). Then, although they could not consciously discriminate between the weights, they asked each other to try to identify the heavier weight anyway, and to indicate on a scale running from 0 to 3 the degree of confidence they had in each guess. Naturally, on almost all trials both men chose 0. But despite their lack of confidence, they in fact chose the correct object on more than 60 percent of the trials, significantly more than would have been expected by chance. And when Peirce and Jastrow repeated the experiment in other contexts, such as judging surfaces that differed slightly in brightness, they obtained a comparable result—they could often correctly guess the answer even though they did not have conscious access to the information that would allow them to come to that conclusion. This was the first scientific demonstration that the unconscious mind possesses knowledge that escapes the conscious mind.

Peirce would later compare the ability to pick up on unconscious cues with some considerable degree of accuracy to “a bird’s musical and aeronautic powers … it is to us, as those are to them, the loftiest of our merely instinctive powers.” He elsewhere referred to it as that “inward light … a light without which the human race would long ago have been extirpated for its utter incapacity in the struggles for existence.” In other words, the work done by the unconscious is a critical part of our evolutionary survival mechanism.4 For over a century now, research and clinical psychologists have been cognizant of the fact that we all possess a rich and active unconscious life that plays out in parallel to our conscious thoughts and feelings and has a powerful effect on them, in ways we are only now beginning to be able to measure with some degree of accuracy.

Carl Jung wrote, “There are certain events of which we have not consciously taken note; they have remained, so to speak, below the threshold of consciousness. They have happened, but they have been absorbed subliminally.”5 The Latin root of the word “subliminal” translates to “below threshold.” Psychologists employ the term to mean below the threshold of consciousness. This book is about subliminal effects in that broad sense—about the processes of the unconscious mind and how they influence us. To gain a true understanding of human experience, we must understand both our conscious and our unconscious selves, and how they interact. Our subliminal brain is invisible to us, yet it influences our conscious experience of the world in the most fundamental of ways: how we view ourselves and others, the meanings we attach to the everyday events of our lives, our ability to make the quick judgment calls and decisions that can sometimes mean the difference between life and death, and the actions we engage in as a result of all these instinctual experiences.

Though the unconscious aspects of human behavior were actively speculated about by Jung, Freud, and many others over the past century, the methods they employed—introspection, observations of overt behavior, the study of people with brain deficits, the implanting of electrodes into the brains of animals—provided only fuzzy and indirect knowledge. Meanwhile, the true origins of human behavior remained obscure. Things are different today. Sophisticated new technologies have revolutionized our understanding of the part of the brain that operates below our conscious mind—what I’m referring to here as the subliminal world. These technologies have made it possible, for the first time in human history, for there to be an actual science of the unconscious. That new science of the unconscious is the subject of this book.


PRIOR TO THE twentieth century, the science of physics described, very successfully, the physical universe as it was perceived through everyday human experience. People noticed that what goes up usually comes back down, and they eventually measured how quickly the turnaround occurs. In 1687 Isaac Newton put this working understanding of everyday reality into mathematical form in his book Philosophiae Naturalis Principia Mathematica; the title is Latin for Mathematical Principles of Natural Philosophy. The laws Newton formulated were so powerful that they could be used to accurately calculate the orbits of the moon and faraway planets. But around 1900, this neat and comfortable worldview was shaken. Scientists discovered that underlying Newton’s everyday picture is a different reality, the deeper truth we now call quantum theory and relativity.

Scientists form theories of the physical world; we all, as social beings, form personal “theories” of our social world. These theories are part of the adventure of participating in human society. They cause us to interpret the behavior of others, to predict their actions, to make guesses about how to get what we want from them, and to decide, ultimately, on how we feel toward them. Do we trust them with our money, our health, our cars, our careers, our children—or our hearts? As was true in the physical world, in the social universe, too, there is a very different reality underlying the one we naively experience. The revolution in physics occurred when, in the nineteenth and early twentieth centuries, new technologies exposed the exotic behavior of atoms and newly discovered subatomic particles, like the photon and electron; analogously, the new technologies of neuroscience are today enabling scientists to expose a deeper mental reality, a reality that for all of prior human history has been hidden from view.

The science of the mind has been remade by one new technology in particular. Functional magnetic resonance imaging, or fMRI, emerged in the 1990s. It is related to the ordinary MRI that your doctor employs, except fMRI maps the activity of the brain’s different structures by detecting the blood flow that waxes and wanes, just slightly, as that activity varies. In this way fMRI offers three-dimensional pictures of the working brain, inside and out, mapping, to a resolution of about a millimeter, the level of activity throughout the organ. To get an idea of what fMRI can do, consider this: scientists can now use data collected from your brain to reconstruct an image of what you are looking at.6

Have a look at the pictures below. In each case, the image on the left is the actual image a subject was gazing at, and the image on the right is the computer’s reconstruction. The reconstruction was created from the fMRI’s electromagnetic readings of the subject’s brain activity, without any reference to the actual image. It was accomplished by combining data from areas of the brain that respond to particular regions in a person’s field of vision together with data from other parts of the brain that respond to different themes. A computer then sorted through a database of six million images and picked the one that best corresponded to those readings.


Courtesy of Jack Gallant

The result of applications like this has been an upheaval as radical as that of the quantum revolution: a new understanding of how the brain operates, and who we are as human beings. This revolution has a name, or at least the new field that it spawned has one. It is called social neuroscience. The first official meeting ever devoted to that field took place in April 2001.7

CARL JUNG BELIEVED that to learn about the human experience, it was important to study dreams and mythology. History is the story of events that played out in civilization, but dreams and myths are expressions of the human heart. The themes and archetypes of our dreams and myths, Jung pointed out, transcend time and culture. They arise from unconscious instincts that governed our behavior long before civilization papered over and obscured them, and they therefore teach us about what it means to be human on the deepest level. Today, as we piece together how the brain works, we are able to study human instincts directly, to see their physiological origins within the brain. It is by uncovering the workings of the unconscious that we can best understand both how we are related to other species and what makes us uniquely human.

The upcoming chapters are an exploration of our evolutionary heritage, of the surprising and exotic forces at play beneath the surface of our own minds, and of the impact of those unconscious instincts on what is usually considered willed, rational behavior—an impact that is much more powerful than we have previously believed it to be. If you really want to understand the social world, if you really want to understand yourself and others, and, beyond that, if you really want to overcome many of the obstacles that prevent you from living your fullest, richest life, you need to understand the influence of the subliminal world that is hidden within each of us.