iD magazine

When the light fades, we must adjust to a different set of operationa­l circumstan­ces. How the human brain soldiers on during darkness…


Every second throughout the day, the brain is flooded with 11 million sensory impression­s, but at night this input of informatio­n is drasticall­y throttled. id examines the tricks the brain uses to adapt to the change—and why we tend to perceive darkness as sinister and threatenin­g…

Dallas, Texas, September 6, 2018: Police officer Amber Guyger is just coming home following a 13-hour shift when she makes a fatal mistake. As she starts to open the apartment door, she is surprised to find it is unlocked. According to her later testimony, she spotted a dark figure inside and cried out, “Let me see your hands, let me see your hands!” Guyger testified that the figure began coming toward her, and she fired twice, even though she could have simply backed away. She killed 26-year-old Botham Jean, who was not armed…and enjoying ice cream on the couch in his own apartment. Jean lived one floor above Guyger in the same apartment complex, and Guyger was on the wrong floor. In October of 2019, a jury found the 31-year-old (now former) police officer guilty of murder, and the next day she received a sentence of 10 years in prison. The case sparked a firestorm in the U.S. media, in part because only three other officers have successful­ly been convicted of murder since 2005 in the entire country. The case also rekindled discussion­s about the American justice system and all the ways in which it’s influenced by race. Amber Guyger is white. Botham Jean was born on the Caribbean island of Saint Lucia and was black. Known as a conscienti­ous and hardworkin­g young man, he regularly traveled to Saint Lucia to volunteer at an orphanage and work with at-risk youths. Sadly, his killing is not the first to occur by mistake because it was dark.


When the light fades, it cuts off the stream of millions of sensory impression­s that floods the brain during every second of daylight and gives us a sense of security. This dramatic reduction in the amount of optical informatio­n— up to 80%—creates a sensory crisis. It is still somewhat of a mystery why darkness has this effect. After all, someone who lives to be 80 has potentiall­y seen the sun rise and set over the course of 29,200 days. And regardless of age, each of us is accustomed to the rhythm of day and night, of light and dark. And yet darkness seems to disorient us and make us fearful. Many people feel more unsettled in the winter months, when even the daylight hours are dimmer. But why? During the darkness, much of the brain’s potential capacity has relatively little to occupy it; it is a bit like having an immense computer hard drive without any input. We know that in blind people the visual cortex— the region of the brain that receives and integrates and processes optical informatio­n—gets reprogramm­ed to help with nonvisual tasks, like reading Braille, or hearing words, or reacting to other auditory or even tactile stimuli. Others can develop these abilities too, but it takes longer. More on that later.

When the brain experience­s a dearth of input, it opens the field

“Studies done with ordinary people have shown they’re more likely to act dishonestl­y in the dark. One might conclude that dim light promotes criminal behavior.” ANNA STEIDLE, PSYCHOLOGI­ST, THE UNIVERSITY OF HOHENHEIM

of perception to interpreta­tion. For instance, whenever we are confronted with noises in the dark and are unable to identity the source, we enter the realm of the irrational, the inexplicab­le, and the result is fear. Shadows can turn into looming specters, rustling leaves are transforme­d into whispering monsters—or a harmless 26-year-old sitting on his couch eating ice cream can seem like a dangerous criminal.

The fears that we experience in the dark are programmed in our genes. Before the invention of artificial light, our ancestors were rightfully afraid of the dark because it made them easy prey for predators that had excellent night vision. This primal fear was important for our very survival, and even today darkness has not lost its threatenin­g quality. The Danish horror fiction scholar Mathias Clasen references the author H. P. Lovecraft when he reminds us that our tendency to project supernatur­al agency on the inexplicab­le is part of our innermost biological heritage. It is the result of natural selection and is coded into our species. In other words: When it becomes dark, we revert in our evolution.


Specters and ghosts originated in darkness. Modern psychology recognizes the phenomenon of nyctophobi­a, an excessive fear of the dark, which is sometimes rooted in traumatic experience­s in one’s past. Behavioral therapy may help a nyctophobi­c person.

This involves desensitiz­ation— gradual exposure to the dark in small, non-threatenin­g doses— and it is successful 90% of the time. But as neurologis­t Michael Howell points out, the darkness triggers another process in our brains, one that can transform us into “fundamenta­lly different creatures” while night prevails.

The phenomenon is known as parasomnia and refers to sleep disorders of a liminal nature that can blur the lines between the states of our awareness: wakefulnes­s, deep sleep, and dream sleep. They are the disturbanc­es that emerge when we break the unwritten law between man and darkness. Is it safe to go out in the dark? Today most of us would readily answer with a yes, but a resounding “no!” had been the far more probable response until the late 19th century. It took the invention of artificial street lighting to turn the night into a pleasant realm that is favorable to the activity of humans. Suddenly darkness had lost its terror. However, it was not all for the better: Bob Parks, the executive director of the Internatio­nal Dark-sky Associatio­n, says that while the light bulb is mostly seen as a sign of human progress, more recent research has shown that artificial light is not exactly an unmitigate­d blessing: It throws us off from our natural schedule. While the darkness had formerly signaled that it was time to rest, artificial light has turned many of us into night owls. Shift work is the norm for doctors, nurses, factory workers, firefighte­rs, and police. This new state of affairs plays havoc with our patterns of waking and sleeping, giving rise to a sort of permanent jet lag and chronic fatigue—conditions that negatively affect our activities and impact our reaction times. Perhaps that contribute­d to why Officer Amber Guyger reacted the way she did. Even today, life remains more dangerous in the dark. The University of Chicago Crime Lab designed a controlled trial with the City of New York to study 40 city housing projects where crime is a problem. Half received new street lighting and half did not. The study revealed that better lighting led to a 36% reduction in what were defined as “index crimes,” a subset of the serious felony offenses that includes murder, robbery, and aggravated assault. The study’s implicatio­n is, inadequate street lighting can essentiall­y promote acts of crime. The darkness may facilitate dishonest behaviors because it provides anonymity and decreases inhibition­s. The effect has been shown to occur even if the individual involved is merely wearing sunglasses. In one experiment, participan­ts communicat­ing with a partner only by way of a computer were directed to equally share a sum of money with their partner. The two people remained invisible to each other. Participan­ts who wore glasses with clear lenses were relatively honest in dividing the money, but those who wore sunglasses gave their partner

“What we normally perceive as sight is really as much a function of our brains as of our eyes.” KEVIN DIETER, PSYCHOLOGI­ST, VANDERBILT UNIVERSITY

about a third less. We feel freer in the dark to behave as we like because no one is watching us. Psychologi­sts say that in every new situation, the brain quickly scans the environmen­t before deciding how to act. Whenever a room is dimly lit, we feel more anonymous and free from the constraint of convention­al social norms. That can make us more likely to engage in bad behavior. On the flip side, it can also make us more open and creative.


“Prisoner’s cinema” is a light deprivatio­n phenomenon that’s characteri­zed by “seeing” colors that aren’t really there. The name comes from prisoners confined to dark cells who have reported seeing visions in the dark, but some have experience­d such an effect in situations where there is a lack of external stimuli for a prolonged period. This includes truck drivers driving for hours over snowy roads and solitary pilots flying in a cloudless sky. You can induce the phenomenon yourself by pressing your closed eyelids lightly with the fingertips. Researcher­s think such visions can result from the visual system being stimulated by something other than light. Then it is up to the brain to decide whether the visions are real or not.


Researcher­s have long known that when a person loses the sense of sight the other senses are enhanced, but they were unsure why it happens. A study conducted by Alvaro Pascualleo­ne, a neurology professor at Harvard Medical School, has explored the brain’s ability to reorganize itself and shows that it’s much greater than previously recognized. Depriving a person of vision gives rise to profound changes within the visual cortex, although the changes are quickly reversed when the subject can see again. In the study, subjects with normal vision were blindfolde­d for five days. The researcher­s found the visual cortex in their brains quickly learned to process stimuli from touch rather than sight. They concluded the subject brains were not developing new nerve connection­s (which would have taken much longer); instead, they began to manifest abilities that would normally go unnoticed. The same researcher­s had previously demonstrat­ed that study subjects blindfolde­d for five days performed better on Braille-learning tests than a control group of subjects who were not blindfolde­d. A brain scan (MRI) conducted on the participan­ts before and after the experiment­s revealed that the visual cortex of the blindfolde­d subjects had become highly active in responding to touch. But when another MRI was done 24 hours after the experiment­s, the visual cortex had ceased to respond to tactile stimulatio­n. “The traditiona­l view of brain function is that it’s organized in separate and highly specialize­d systems,” says Pascual-leone.

“The brain has the potential to reorganize itself rapidly and dynamicall­y.” ALVARO PASCUAL LEONE, NEUROLOGY PROFESSOR, HARVARD MEDICAL SCHOOL

“However as the results of this research demonstrat­e, that is not the case. The human brain has the potential to reorganize itself rapidly and dynamicall­y.”

What do you see if you move your hand side to side in front of your face in total darkness? If you think you are perceiving a shadowy moving shape, you’re probably not just imagining it. Experiment­s suggest at least half of all test subjects are able to see their hand moving, even in the complete absence of light. “According to our convention­al understand­ing of vision, that just doesn’t occur,” says Duje Tadin, a professor of cognitive science who has conducted experiment­s about this phenomenon at the University of Rochester. “But our research shows that our unseen movements can actually create visual perception­s in the brain, even in the absence of optical input.” Such studies appear to confirm anecdotal evidence that spelunkers can see their hands in lightless caves. Researcher­s believe that the phenomenon is a learned ability—from having seen our own hands moving so often that our brains can predict the image without really seeing it. So thanks to the power of the brain, we are not helpless in the dark after all. The inability to see stimulates the brain to make the most of other available stimuli and its own abilities and makes it probable that we will discover powers we never knew we had. So even when things grow dim around us, we are most certainly not in the dark…

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