Subliminal

you look at your boss, for example, the true retinal image would show a fuzzy, quivering person with a black hole in the middle of his or her face. However emotionally appropriate that may seem, it is not an image you’ll ever perceive, because your brain automatically processes the data, combining the input from both eyes, removing the effects of the jiggling, and filling in gaps on the assumption that the visual properties of neighboring locations are similar. The images below illustrate some of the processing your brain does for you. On the left is the scene as recorded by a camera. On the right is the same image as it would appear if recorded by a human retina with no additional processing. Fortunately for you, that processing gets done in the unconscious, making the images you see as polished and refined as those picked up by the camera.

Our hearing works in an analogous manner. For example, we unconsciously fill in gaps in auditory data. To demonstrate this, in one study experimenters recorded the sentence “The state governors met with their respective legislatures convening in the capital city,” then erased the 120-millisecond portion of the sentence containing the first “s” sound in “legislatures” and replaced it with a cough. They told twenty experimental subjects that they would hear a recording containing a cough and would be given printed text so they could circle the exact position in the text at which the cough occurred. The subjects were also asked if the cough had masked any of the circled sounds. All of the volunteers reported hearing the cough, but nineteen of the twenty said that there was no missing text. The only subject who reported that the cough had obscured any phonemes named the wrong one.²⁵ What’s more, in follow-up work the researchers found that even practiced listeners couldn’t identify the missing sound. Not only could they not pinpoint the exact location of the cough—they couldn’t even come close. The cough didn’t seem to occur at any clear point within the sentence; rather, it seemed to coexist with the speech sounds without affecting their intelligibility.

^{Original image, made by a camera. The same image seen by a retina (right eye, fixation at the X.)}

^{Courtesy of Laurent Itti.}

Even when the entire syllable “gis” in “legislatures” was obliterated by the cough, subjects could not identify the missing sound.²⁶ The effect is called phonemic restoration, and it’s conceptually analogous to the filling in that your brain does when it papers over your retinal blind spot, and enhances the low resolution in your peripheral vision—or fills holes in your knowledge of someone’s character by employing clues based on their appearance, their ethnic group, or the fact that they remind you of your uncle Jerry. (About that, more later.)

Phonemic restoration has a striking property: because it is based on the context in which you hear words, what you think you heard at the beginning of a sentence can be affected by the words that come at the end. For example, letting an asterisk denote the cough, listeners in another famous study reported hearing the word “wheel” in the sentence “It was found that the *eel was on the axle.” But they heard “heel” when they listened to the sentence “It was found that the *eel was on the shoe.” Similarly, when the final word in the sentence was “orange” they heard “peel,” and when it was “table,” they heard “meal.”²⁷ In each case the data provided to each subject’s brain included the same sound, “*eel.” Each brain patiently held the information, awaiting more clues as to the context. Then, after hearing the word “axle,” “shoe,” “orange,” or “table,” the brain filled in the appropriate consonant. Only at that time did it pass to the subject’s conscious mind, leaving the subject unaware of the alteration and quite confident of having accurately heard the word that the cough had partially obscured.

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IN PHYSICS, SCIENTISTS invent models, or theories, to describe and predict the data we observe about the universe. Newton’s theory of gravity is one example; Einstein’s theory of gravity is another. Those theories, though they describe the same phenomenon, constitute very different versions of reality. Newton, for example, imagined that masses affect each other by exerting a force, while in Einstein’s theory the effects occur through a bending of space and time and there is no concept of gravity as a force. Either theory could be employed to describe, with great accuracy, the falling of an apple, but Newton’s would be much easier to use. On the other hand, for the calculations necessary for the satellite-based global positioning system (GPS) that helps you navigate while driving, Newton’s theory would give the wrong answer, and so Einstein’s must be used. Today we know that actually both theories are wrong, in the sense that both are only approximations of what really happens in nature. But they are also both correct, in that they each provide a very accurate and useful description of nature in the realms in which they do apply.

As I said, in a way, every human mind is a scientist, creating a model of the world around us, the everyday world that our brains detect through our senses. Like our theories of gravity, our model of the sensory world is only approximate and is based on concepts invented by our minds. And like our theories of gravity, though our mental models of our surroundings are not perfect, they usually work quite well.

The world we perceive is an artificially constructed environment whose character and properties are as much a result of unconscious mental processing as they are a product of real data. Nature helps us overcome gaps in information by supplying a brain that smooths over the imperfections, at an unconscious level, before we are even aware of any perception. Our brains do all of this without conscious effort, as we sit in a high chair enjoying a jar of strained peas or, later in life, on a couch, sipping a beer. We accept the visions concocted by our unconscious minds without question, and without realizing that they are only an interpretation, one constructed to maximize our overall chances of survival, but not one that is in all cases the most accurate picture possible.

That brings up a question to which we will return again and again, in contexts ranging from vision to memory to the way we judge the people we meet: If a central function of the unconscious is to fill in the blanks when there is incomplete information in order to construct a useful picture of reality, how much of that picture is accurate? For example, suppose you meet someone new. You have a quick conversation, and on the basis of that person’s looks, manner of dress, ethnicity, accent, gestures—and perhaps some wishful thinking on your part—you form an assessment. But how confident can you be that your picture is a true one?

In this chapter I focused on the realm of visual and auditory perception to illustrate the brain’s two-tier system of data processing and the ways in which it supplies information that does not come directly from the raw data in front of it. But sensory perception is just one of many arenas of mental processing in which portions of the brain that operate at the unconscious level perform tricks to fill in missing data. Memory is another, for the unconscious mind is actively involved in shaping your memory. As we are about to see, the unconscious tricks that our brains employ to create memories of events—feats of imagination, really—are as drastic as the alterations they make to the raw data received by our eyes and ears. And the way the tricks conjured up by our imaginations supplement the rudiments of memory can have far-reaching—and not always positive—effects.

CHAPTER 3 Remembering and Forgetting How the brain builds memories … why we sometimes remember what never happened

A man sets himself the task of portraying the world. Through the years he peoples a space with images of provinces, kingdoms, mountains, bays, ships, islands, fishes, rooms, instruments, stars, horses, and people. Shortly before his death, he discovers that the patient labyrinth of lines traces the image of his face.

—JORGE LUIS BORGES

JUST SOUTH OF the Haw River in central North Carolina lies the old mill town of Burlington. It’s a part of the country that is home to blue herons, tobacco, and hot, humid summer nights. The Brookwood Garden Apartments is a typical Burlington complex. A pleasant single-story building made of gray brick, it is situated a few miles east of Elon College, now Elon University, a private school that, with the decline of the mills, came to dominate the town. On one of those hot nights in July 1984, a twenty-two-year-old Elon student named Jennifer Thompson was asleep in bed when a man snuck up to her back door.¹ It was three o’clock in the morning. As her air conditioner hummed and rattled, the man cut Jennifer Thompson’s phone line, busted the lightbulb outside her door, and broke in. The noise was not enough to rouse her from her sleep, but the man’s footsteps inside her apartment