In popular culture, black and white are thought of as simple opposites, but my colleague Jose-Manuel Alonso and I have been uncovering ways that we perceive black and white differently, and how our brains have evolved mechanisms that create these differences. I want to walk you through some of our experiments that have led to an interesting answer to a 400-year-old puzzle.

If you look at the left side of the two busts of Caesar paired at the top, you’ll see a three-dimensional white sculpture, because we interpret the two-dimensional variations of brightness in the image as shading caused by light reflected from an object. In the photo on the right, we perceive essentially the same three-dimensional shape, but lit from the opposite side, and appearing to be made of a darker material. So not only is our judgment of the illumination different, but so is our judgment of the object’s material properties. This photo is just the contrast reversal (photo negative) of the photo with the white bust, so comparing the two illustrates how we interpret gradual variations of light versus variations of dark.

The difference in how we use black and white cues to infer the properties of an object is even more evident when the changes in brightness are more distinct. The bright streaks on the black bust above appear to be highlights, and from their sharpness and small scale relative to the object, we can estimate the glossiness of the material. If the contrast of the image is reversed (the right side of the image pair above), we see a white or even metallic bust, and the black streaks appear to be smudges or paint. In this situation the two tones give entirely different sorts of clues about illumination and material properties.

These examples illustrate a basic asymmetry in the way we perceive white and black: We interpret difference in lights as information about illumination, while differences in darks reveal something about materials. These interpretations fit well with the physics of the world: Illuminants light up objects, and are reflected less by highly absorbent materials and holes.

Other basic asymmetries have been noted for centuries. Galileo Galilei, who was as perceptive as he was creative, observed that Venus appeared larger through his telescope as a light object against the dark night sky than it appeared as a dark object against the bright day sky. Ernst Mach, for whom the speed of sound is named, demonstrated that letters are difficult to recognize if some strokes are white and others black, suggesting that the two shades may be processed separately by the brain.

We began our experiments by testing whether subjects could pick out blacks and whites on unbiased backgrounds with equal ease. We created randomly arranged background panels with an equal number of equal-sized black and white pixels, and then asked observers to count the number of larger targets presented on the background as quickly as possible. To make the targets clearly different from the background pixels, we made them nine times larger in area. The targets were either all black or all white. To our surprise we found that people counted black targets significantly faster and with many fewer errors. You can see that black targets are easier to identify than white ones in these 12 examples:

How could we explain this discrepancy? Galileo had attributed the illusion of Venus’ size to light scatter in the eye, which would enlarge the image of a light area compared to a dark area. Herman von Helmholtz, the polymath physicist and physician, showed that there was too little light scatter in the eye for Galileo’s explanation to be complete, but the actual cause remained unclear. Helmholtz took Galileo’s observation and made a simpler, abstract version of it with equal-sized white and black squares on the opposite backgrounds. The white square appeared larger, so he called it the “irradiation illusion.” We noticed that something akin to the irradiation illusion was occurring in our backgrounds, too: Even though there were equal areas of black and white, there appeared to be more white area.

We measured the magnitude of Helmholtz’s irradiation illusion by asking people to increase the area of the black square until it appeared to be the same size as the white. Then we calculated the ratio of the physical sizes of the squares. Similarly, we measured the magnitude of the area illusion in the background by having people increase the ratio of black to white pixels until the areas appeared equal. Since the ratios required by the two corrections were approximately equal, we reasoned that both illusions must share an underlying cause. We became more convinced that our ability to see black versus white targets was influenced by the irradiation illusion when we found that if we used backgrounds with what people saw as the “balanced” ratio of black to white, targets of the two shades were equally easy for viewers to see and count.

Our next step was to search for a brain mechanism that could explain the irradiation illusion. When Keffer Hartline recorded the first electric signals from single retinal nerves responding to light stimulation, he found two types of nerves whose responses are shown on the left side of the figure below. One kind of neuron generated spiking electrical signals when exposed to light (bottom two rows). The other kind generated spikes in the dark, but turned off when exposed to light (top row). Since then, such cells have been found in eyes of many species as disparate as insects and mammals, separated by more than 500 million years of distinct evolutionary pressures, suggesting that this neural strategy fits something fundamental about the world, across many environmental niches.

These neurons are called ON and OFF cells, because of their behavior in response to light. Until recently, they had been generally considered to be opposite but equal. However, we found that when we measured the responses of ON cells to increasing equal increments of light on a black background, the response increased rapidly but then plateaued (red curve). On the other hand, OFF cell responses increased roughly in a straight line as light was decreased on a white background (blue curve). The more rapid initial increase in ON outputs explains why we are more sensitive to small increases of light in dark settings than to small decreases of light in bright settings. The plateau at the top of the ON response curve explains why we are more limited at distinguishing progressively lighter shades than we are darker shades. The neural explanation for both the irradiation illusion and Galileo’s observation arises from the same difference in the response curves.

Remarkably, these simple but different responses of the ON and OFF cells also explain some black-white asymmetries that seem almost paradoxical. For example, it is easier to make out black text on a white background than white text on a black background, despite the fact that we are capable of seeing much tinier white dots on black backgrounds than black dots on white backgrounds. The reason for this is that the ON response expands strokes of white letters slightly so that they become more difficult to distinguish. The same effect “expands” a white background, making small black dots seem smaller.

Whites and blacks in images of the world thus arise from different physical causes, provide information about different aspects of the world, and are processed differently by the brain. The differences in how we see shades originate in the beginnings of sensory neural processing. We have yet to figure out the neural mechanisms that allow us to make inferences about illumination and materials from different scales of lights and darks, so we may have much to learn from the strategies that artists use to depict them. If you look at black and white drawings not as impoverished versions of the colored world, but as pared-down illustrations of the cues we use to understand what we are looking at, you can enjoy them as intellectual puzzles, and it may change the way you look at art.

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My work starts on dark, black nights, when there is no moon or reflection from it. The telescopes I use have to be in places with three qualities: High, dry, and—you guessed it—very dark. And so, I search for planets atop the summit of the highest, driest, and darkest peak in Hawaii. Mauna Kea, a dormant volcano—where the world-famous Keck Observatory is located—minimizes the “noise” in the images from Earth’s constantly swirling atmosphere and the light drifting in from cities.

Because black is defined by the absence of light, you might not think there are different gradations of black—but there are when you are hunting for other planets in our galaxy. Every day, I am looking through images that appear, at first, like exposures devoid of any light. In reality, shades of black can hide amazing worlds—some of which could be habitable or inhabited by life forms.

Seeing the color black in fact is a comforting affirmation that I’m searching in the right direction, for a planet must be so faint as to appear to not be there at all. If an image has many bright dots of light, that means I am looking at a field full of stars. I am not interested in objects that emit their own light. A star is too extreme an environment for life as we know it—it’s an enormous ball of hot plasma and even if it had a solid surface to stand on, which it doesn’t, life forms like us would get crushed under the star’s tremendous gravitational pull.

What I’m trying to find are very faint objects that reflect and re-emit the light from a host star nearby. These planets outside our solar system—which are known as exoplanets—are companions to stars, swimming in their own sea of darkness. Finding these planets tells us about the architecture of planetary systems. It also lets us know how common exoplanets are in the habitable regions around stars, where the temperatures are not too hot and not too cold, where liquid water can exist, and complex molecules may have figured out the processes we call life.

Sample image of searching for a planet around a mature star, taken in March 2016 with the NIRC2 camera on Keck II telescope.

 
My research uses the newest planet-hunting technique—“direct imaging.” Put simply, we place a small piece of black film in the field of view of the telescope to dampen the light from the parent star. Then, astronomers like myself can make out the faint planet companions orbiting the star. We rotate the powerful Keck telescope, taking pictures in a time-lapsed sequence, and then apply an intensive mathematical data analysis procedure. Through this process, we can carefully distinguish the feeble signal of a planet from the overwhelming glow of the host star. The dark piece of film is called a coronagraph, and it is a key component of the direct imaging technique.

That’s right, I am actually trying to make the picture darker because the natural blackness of space is not enough to be able to see what we want to see. In order to extract the signal of a planet in an image, there is a lot of interference I have to take out: the random noise from the camera’s own electronics, the scattered light around the coronagraph, and the rotation of the individual exposures. The final image, a deeper tone of black, is the result of stacking cleaned-up exposures to reveal a clear signal from the planetary system. Galileo Galilei, the first observational astronomer, would be fascinated to see how we’ve progressed in the last 400 years. We are now seeing planets in the blackness around other stars, very much in the same way he discovered the faint moon companions around Jupiter.

I did not set out to stare at blackness all day long. I came to astronomy by way of mathematics, which is a great tool for designing ways to see very small perturbations in data. But as I learned more about how astronomy could help expand the boundaries of human knowledge, I became more and more interested in trying to see what the universe conceals in the darkness.

Ultimately, this is what all research is—seeking light in the darkness of the unknown. Our bodies are limited by the sensitivity of the human eye, but we have expanded our searches by manipulating the pixels of more sensitive cameras, and can thus capture evidence of real physical phenomena with our machines. If humans are to learn about how we came to be and search for life beyond ourselves, we must continue to look for answers in the deep blackness of space. And of course, we have to combine that with a little patience for staring into what may seem like a lot of nothingness.

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Who was she? The woman who—simply by wearing all black—makes you feel stupidly ostentatious for wearing anything else. Even in yoga class.

Legs over head, I tried to steal a glance to pinpoint why some women look so good in black that you’d rather look at them than the mountains behind them. How do they look like Paloma Picasso while others like students on a budget? What could be easier than wearing all black?

Like most enviable skills, wearing all black is not nearly as easy as it looks. I covered fashion in New York in the 1990s so I spent a lot of time staring across a runway, studying row after row of women in black. (In those pre-Instagram years, the only person not in black was Anna Wintour.) And I think I’ve come up with the secret to pulling it off: It’s all about the grooming and the accessories.

Wear all black without perfect lipstick and hair and you can be mistaken for someone who just can’t be bothered with dry cleaning bills. The woman next to me at yoga—in gym clothes for crying out loud—had nary a hair out of place. Even in sweats, the black Lycra worked as a backdrop for her simple but stunning earrings.

Which is why the most successful wearers of all black tend to hail from the design industry. They are the kind of people who can find integrity in a chair, or distinguish a deep, rich blue-black (good) from a faded grey-black (bad—a sign of a garment in need of replacing) at 20 paces. They are ruthless in their design aesthetic—and nothing draws attention to good design better than removing anything, like color, that distracts from it. Similarly, the beatniks wore black to underscore their intellectual rigor. Nothing said square like Lily Pulitzer prints.

In matters of wearing black, it seems little has changed in the last 50 years. A recent study by a U.K. T-shirt manufacturer found that people who wear all black are seen as serious and reliable compared to their chromatic brethren. Which explains why it’s so common in boardrooms—even though a shapeless black suit doesn’t have any of the same appeal as the well-tailored pieces worn by the design cognoscenti.

“When you go to the office, a business meeting or networking event, everyone is wearing black, or gray,” says Jacqueline Allen, the founder of Edit-London, a personal styling firm that focuses only on executives. “The net result is that no one looks particularly senior, distinguished, or influential because everyone looks generic. Rather than enhancing the individual it becomes an equalizer and, instead of appearing unique and authoritative, you appear diminished and lacking confidence.”

For those without a personal stylist, black can also seem safe and speedy. Safe, because if you’re not at the top of the corporate ladder, standing out might be more risky than blending in. Speedy, because it limits the number of decisions to be made in the early morning hours. But unless you get the details perfect, you risk fading away into the background.

Outside of corporate life, color and prints are more popular than ever, but need to be worn with care. Standing out is risky business—remember it was Joseph’s coat of many colors that got him into trouble with his brothers.

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Ozzie’s my fourth black dog. Starting with a sweet Labrador mix in childhood, I have nurtured a love affair with dark-coated canines for decades. I’m not alone in this bias; Labrador retrievers are the most popular dog breed, according to the American Kennel Club, and black labs in particular are bred for their intelligence, energy, and protectiveness. My childhood companion, Lena, was a well-mannered black lab/springer spaniel mix who had all of these qualities in abundance. She was a constant companion on road trips, family outings to the park, and even at my father’s office.

Yet if you listen to many animal workers, and many pet owners, you would think my infatuation is unusual. Black animals generally are thought to repel, not attract. Humane shelters report that large black dogs have more trouble finding homes than do other dogs. The phenomenon even has a name: black dog syndrome.

There are practical explanations. Black animals can be frightening. Black animals of all sizes and breeds are harder to photograph in the shadows of a kennel. Their expressions are harder to read due to the lack of facial contrast. But as a psychologist, I’ve studied the phenomenon, and my research suggests that the explanation for this syndrome, if it actually exists, has nothing to do with the nature of the animal. Instead, it’s based in the cultural associations of the color black itself.

Across nations, folklore, literature, and popular culture have long portrayed black animals as undesirable. Black is widely perceived as the color of evil and doom. The Egyptian god of the underworld, Anubis, was depicted as a black dog (or as a man with a dog’s head) to represent the discoloration of a corpse after embalming. In the folklore of the British Isles, a black dog was a ghostly being whose appearance was regarded as a harbinger of death. Perhaps drawing on this cultural metaphor, Sir Arthur Conan Doyle used the image of a black dog as his specter of horror in The Hound of the Baskervilles. The term “black dog” has been used since at least as far back as Samuel Johnson to describe the darkest depths of depression. Black cats also have negative connotations. In the Middle Ages, they were associated with witchcraft, often joining their owners in a fiery death at the stake. In much of the western world, they still are perceived as unlucky. (Although in parts of Asia and the United Kingdom, black cats actually are associated with good luck—except when one crosses an intended path.)

Psychological research confirms these traditional associations. In one study, for instance, the penalty records of National Football League and National Hockey League teams with black uniforms were found to rank near the top of the leagues. Furthermore, people who looked at pictures of these teams consistently dubbed them as more “aggressive” and “bad” than teams wearing lighter colors. These findings suggest that the color black may bias the judgments of referees, and even increase the aggressiveness of players themselves.

Conversely, studies also show that vibrant color, and especially color contrast, is highly appealing. Attractive color has been identified as a critical factor in product purchases in up to 90 percent of impulse buys. Web design research indicates that contrast in color (known as the isolation effect) can visually guide people to click on computer images. Color seems to be an important feature of branding in all fields of marketing, including pets.

But surprisingly, in the case of dogs, these psychological associations actually might not matter. Black dog syndrome, as a psychological phenomenon, is probably nonexistent. Since my early research on the topic, numerous studies have found that the syndrome may simply be an artifact of something called “base rate fallacy.” Due to the dominance of the dark-coat color gene, there are more black dogs and cats than any other color. This preponderance makes it appear that these animals are disproportionately represented in the shelter population. Moreover, contemporary research shows that prejudice against black dogs is not as prevalent as previously thought. In a 2013 study, participants were asked to rate pictures of dogs, colored black or white but otherwise identical, in terms of their perceived personality attributes. The white dog was rated less friendly and more dominant. Several other animal welfare researchers have confirmed that for dogs, coat color is less important to human perceptions of canine temperament than breed or other physical features such as size, ear conformation, facial features, and tail length.

Black cats, on the other hand, are a different story. They’ve been the focus of less empirical study, but research that controls for factors such as sex or age has found that black cats do in fact take longer to adopt from animal shelters than their lighter or multi-colored peers. Despite the fact that black coat color seems to be genetically linked to friendlier disposition and better health in cats, black cats are thought to be more energetic, aloof, and bold than multi-colored or lighter colored felines. And the additional time spent incarcerated contributes to a vicious cycle. The longer cats spend in shelters, the more their health and emotional well-being declines, which makes them even less desirable.

Whether it’s real or not in a technical sense, black dog syndrome still sometimes may have real effects. The simple belief that the phenomenon exists may be leading to something of a self-fulfilling prophecy: People might hesitate to adopt black dogs because of information they barely remember, or information from a less-than-credible source (a common cognitive heuristic called “source monitoring error”). As a result, fewer may be adopted, and the false beliefs may be perpetuated. And the consequences can be deadly. When shelter workers make assumptions about adoptability based on coat color, euthanasia may be disproportionately used to reduce the numbers of shelter animals that are alleged to be unadoptable.

Thankfully, there’s a growing push for us to recognize our misguided assumptions. Last year, one Utah animal shelter embraced what we know about the importance of appearance in product marketing by hiring a photographer to depict its black animals in a series of glamour shots. The aim was to allow the dogs’ personalities shine through their shadowy exteriors. And it worked; potential adoptive families lined up to meet them.

Ozzie, like all my pets, was a rescue animal. He was taken from a foreclosed house where he lived in a rabbit cage for his first three months. At first, Oz was an unsavory-looking companion, scrawny and timid, and my partner and I wavered before committing to adoption. But my love of black labs won, and now he brings our home so much joy. Like the dogs in the Utah animal shelter’s photographs, he is a reminder that first appearances can be deceptive. With pets, like anything else, color is not always an indicator of what lies beneath.

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