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Sight Unseen

The paradox of blindsight might unlock the mystery of consciousness.

March 21, 2022
by Leah Worthington and Illustration by David Junkin
Artistic rendering of girl with eyes around her

THE FIRST THING Simon Lewis, J.D. ’80, remembers seeing when he opened his eyes was a window, with a faint glow of sunlight. 

It was a beautiful, if mysterious, sight. Though Lewis was a fully grown man, the concept of a window was no more familiar to him than his own name, which was lost to him. 

A month earlier, at age 35, he had survived a horrible accident. It was March 2, 1994. Lewis, a movie producer, and his wife, Marcy, were driving through central Los Angeles when a car going nearly 80 miles per hour T-boned the newlyweds’ Infiniti, sending it flying through the air and into a tree, ultimately landing in someone’s front yard.

Lewis doesn’t remember the crash, but his final words to his wife, about seeing her boss’s new home, were banal. “Let’s take a look after dinner,” he remembers telling her. She died instantly.

When help arrived on the scene, they must have thought him dead as well. Only hours later, after jaws of life were used to pry his body from the wreckage, did they find a pulse. Lewis was rushed to the hospital, where he was intubated and eventually put into a deep coma. A doctor quietly warned one of his brothers that no one thought he would wake up. 

A month later, incredibly, he opened his eyes to the light coming through the window. With no memory of himself, his wife, or his family, and no knowledge of where he was, he felt like an alien just arrived on a new planet. “I didn’t notice that my jaw was wired. I didn’t notice that I couldn’t move my body because my pelvis had been crushed, my spine was broken,” he remembers. “I didn’t have a framework of comparison to think, ‘Wait a minute, why am I in this bed? Why can’t I move my arms?’ I didn’t know I had arms. I didn’t know I had a jaw. I didn’t know anything. I was brand new, born at the age of 35.”

Over the course of several months, Lewis underwent arduous therapy, working on everything from walking to regaining his memory. With all that was wrong with him—head trauma, broken bones, amnesia—it took a while for anyone to realize that one of his primary senses was also severely damaged.

In fact, with a third of his right cerebral hemisphere gone, he had completely lost sight in his left field of vision. But further tests detected something peculiar: Lewis could still identify objects his optometrist, Dr. Alan Brodney, presented in his blindspot with surprising accuracy, but with no awareness of actually seeing them. 

“He said, ‘I’m holding a card. Can you see the card?’” Lewis recalls. “And then he said, ‘What color is the card?’ And I said, ‘I can’t see the card. I’ve no idea what color it is.’ I thought it was nuts.” 

But he played along. 

“He could tell me characteristics of the object, even though he was technically blind in that field,” recalls Brodney, who began to realize that he was seeing a classic case of blindsight.

Blindsight, as the name suggests, is a paradoxical condition of simultaneous blindness and sightedness—the discovery of which, more than 50 years ago, completely upended scientists’ understanding of how vision works. Until then, visual perception was believed to follow a single pathway, in which the retina detects and sends signals via the optic nerve through the thalamus and into the primary visual cortex, where information, including color, shape, and orientation, is processed. As far as medical science could determine, damage to the primary visual cortex, also known as the V1 or striate cortex, was as good as turning off the lights.

Blindsight, however, is thought to circumvent the primary visual cortex using a more primitive pathway to the brain. Although not yet fully described, it marks a distinction between conscious and subconscious vision—what we are aware of seeing and what simply arrives in our brains undetected.

The discovery could have profound implications not just for the visually impaired, like Lewis, but also for our very understanding of what it means to see and experience the world. Perhaps, some scientists speculate, if we can illuminate the neural pathways of conscious and subconscious visual perception, we will be able to observe the mechanisms of consciousness itself.

“For many years, for centuries even … we had many, many patients who had lost their vision—they had a gunshot wound or a stroke,” says Nikhil Bhatla, a postdoctoral researcher in Berkeley’s Department of Molecular and Cell Biology who studies blindsight in mice. “And we just assumed they were blind.”

Then, he says, in the 1960s people started experimenting with primates, removing or damaging the primary visual cortex. “And they were very surprised to find that these monkeys were sort of fine. If you did very precise tests, you could find subtle differences in their vision, but they seemed really normal. So it was a little bit of a conundrum.”

“The doctor asked, ‘What color is the card?’ 

And I said, ‘I can’t see the card. I’ve no idea what color it is.’ I thought it was nuts.” 

The conundrum was embodied in Helen, a rhesus monkey later dubbed “a blind monkey that sees everything.” In 1965, a Cambridge researcher named Lawrence Weiskrantz removed Helen’s primary visual cortex.    

For the first 19 months post-operation, she appeared to be almost completely unsighted—as expected. But then Weiskrantz and his fellow researcher began to notice something odd: Occasionally, the movement of a nearby object would catch Helen’s eye, causing her to turn her head.

Intrigued, they started introducing food rewards to elicit the response behavior. Over the course of a few weeks, the researchers trained her to reach out and grasp, with increasing accuracy, things held in front of her.

Within a few years, Helen had graduated from her cage to more complex environments. Brought to a nearby forest, she would approach, then dodge, trees; in the laboratory, she learned to forage for currants scattered on the floor, deftly navigating an ever-changing array of obstacles.

In the coming years, several human subjects displayed conditions analogous to Helen’s. One well-studied patient, known simply as DB, had the right part of his primary visual cortex surgically removed to extract a benign tumor. Like Helen, DB nevertheless showed a striking capacity for visual discrimination. 

He could, for example, identify the presence and orientation of grid lines and detect motion with impressive accuracy. Yet he insisted he couldn’t see the stimuli presented to him in his blindspot, that his responses were just guesses. 

Similarly, in 2008, a completely blind, cane-using patient known as TN was instructed to walk down a hallway that, unbeknownst to him, was strewn with office equipment. Footage from the study shows TN, caneless, expertly navigating around the obstacles, which he claimed he had no recollection of consciously doing.

“The surprise,” Weiskrantz wrote, “is that human subjects with loss of V1 claim they are blind.”

Understandably, the suggestion that those who are functionally blind might be able to see, albeit unconsciously, has inspired doubts. Ian Phillips, a professor of philosophy and brain sciences at Johns Hopkins University, is one such skeptic. 

Phillips argues that the ability to make deliberate and voluntary decisions—such as pointing or navigating a narrow hallway—is itself evidence that people are consciously aware of the objects in front of them and are instead experiencing an “extremely degraded form of vision.” On top of which, he says, some people do report some level of awareness. “So that immediately kind of muddies the water,” he said. 

Others, like Tony Ro ’93, a professor of psychology and biology at The Graduate Center of the City University of New York, find the research more compelling. “I think there’s a lot of evidence for these types of phenomena or experiences that these [blindsight] patients display,” says Ro, who studies perception, consciousness, and attention. 

“Because of its oxymoronic nature, it’s intrinsically very mysterious. On the one hand, you can’t see, and on the other hand, you can.” 

“We’ve been able to induce blindsight in otherwise completely normal individuals,” says Ro, who uses transcranial magnetic stimulation (TMS) to temporarily disrupt brain function in certain regions of his subjects’ visual field. “If you flash the light, you do anything there, they’ll say, ‘I don’t see anything.’” And yet, he adds, “the eye movements and eye movement behavior are not disrupted, even though their awareness of that visual information is disrupted. So we get these really clear dissociations that seem to be consistent with known anatomy and known ways in which the brain should function under these types of conditions.”

The skepticism doesn’t surprise Bhatla, who acknowledges that blindsight, by definition, seems to defy understanding. “Because of its oxymoronic nature, it’s intrinsically very mysterious,” he says. “On the one hand, you can’t see, and on the other hand, you can.” 

That said, blindsight is not sight. The “richness” of visual experience, as Bhatla calls it, is something blindsight patients generally lack even if, like Lewis, they’re able to gradually expand their field of vision.

“They can point to the targets,” he says. “But they don’t have the experience of seeing. They don’t have what I would call, or what philosophers call, quality.”

From a young age, Bhatla found himself drawn to color and light and fascinated by the nature of consciousness. “I remember as a kid, maybe in like, seventh grade, thinking about, ‘Why am I here? Why am I alive? What is the meaning of life?’” he says.

In grad school at MIT, he was surprised to find few people studying what he believed to be fundamental questions about the human experience. “The bulk of biological research, and neuroscience research, isn’t in any of these sort of philosophical domains,” he says. 

Bhatla’s work at Berkeley involves extending previous primate studies to mice that have had part of their visual cortexes removed. While the mice’s discrimination in navigating a maze wasn’t as accurate as before the surgery, it was still three times better than it would be in total blindness. 

“It’s pretty robust,” he says. “It’s robust enough that I can do some real science with it.”

Hillel Adesnik, an associate professor of neurobiology at Berkeley and Bhatla’s advisor, describes the experimental design and initial findings in mice as “awesome.”

With his first trials showing strong evidence of blindsight in mice, Bhatla now has his eyes set on loftier goals, like tracing the evolution and function of consciousness. What, he wants to know, is happening at the cellular, mechanistic level that creates something as singular and mystifying as consciousness? 

In the short term, Bhatla wants to apply modern biotechnology to more precisely identify the cranial regions involved in visual perception. The recent development of optogenetic tools, which use light to selectively stimulate neurons, enables scientists like Bhatla to manipulate neural circuits and ask, essentially, “What does this wire do?”

In the long term, he hopes to trace the pathways of unconscious and conscious vision through the brain to develop a sort of “blueprint” of the neural networks that produce our conscious experience of the world. 

“What you can do in mice is you can break this down according to the circuit elements,” Adesnik says, to identify which cells and pathways are involved in conscious vision. “[Bhatla] has now gone through like 10 different cell types in the cortex,” he says. And, indeed, they’ve shown that “some cell types are actually dispensable, other cell types are critical.”

Such a map, Bhatla says, could even offer insights into the origins of consciousness in evolutionary history. By comparing the brain activity of mice and other animals like worms, researchers might be able to identify when and where consciousness arose—and to what end.

“There’s a second question here,” Bhatla says, explaining that it’s not just how we have a conscious experience of our world, but why

“From a sort of basic scientific point of view, we shouldn’t even be conscious.” 

On the darkest day of his recovery, Lewis tried to give up. 

What was the point in continuing on, he wondered from the prison of his hospital room, if everything that brought meaning and joy to his life was gone? Bedridden and immobile, he pushed his remote off the side of the bed, throwing away the last thing of value in his possession.

“I just didn’t want to be… ” he says, trailing off. “I wanted to be gone.”

In the end, it was a throat infection that yanked him from his depression. 

“When I woke up that morning, my throat was completely choked up,” he remembers, cheerful again. “I realized things can always get worse… and they can always get better.”

Eventually, Lewis found that the blindsight diagnosis gave him language to describe his new experience of reality—and tools to work with what abilities remained. 

“From a sort of basic scientific point of view, we shouldn’t even be conscious.”

Through weekly therapy sessions and exercises designed to expand his peripheral vision, Lewis began to develop greater awareness of his own subconscious knowledge—and an ability to probe it. For instance, driving in focused silence (with the aid of prismatic glasses and after many  specialized lessons) allows him to attend to objects in his blindspot that might otherwise go unnoticed. He says he also learned to ask questions of his subconscious and to let the answers come with time, an experience akin to searching in vain for the name of a band only to have it pop into your head hours later.

Since his accident, Lewis has recovered much of the function in the lower left quadrant of his vision. He’s still impaired in his gait and sight (he recently tripped and broke his humerus and rotator cuff) and suffers from headaches, sensory overload, and chronic fatigue. But he can walk, drive, has given TED Talks, and has even written a book, Rise and Shine, about his experience. Galvanized by his own miraculous survival, he wants his story to be a model for others on a path to recovery. 

“I’m functionally unsighted. There are many things I can’t do,” he says. And yet he embraces his blindsight as a sort of superpower. Where a neuroscientist might see chaos or disjointedness, Lewis sees open-mindedness—and possibility.

“It’s about, each day, celebrating what remains,” he says. “The way I put it is, there’s always reasons for hope, and hope for reason.”

A bush is growing just outside his window, Lewis says. He describes the pattern, from seed to branch to more branches, and the way it bends where shade falls, preferring to catch the light. 

“It’s responding to all kinds of different things,” he says, with admiration. “It’s maximizing”—much like our brains—“to express the fullest range of possibilities.”

Leah Worthington is a Bay Area–based writer, currently reporting for the Redwood City Pulse, and co-host of California’s podcast, The Edge. She has many half-baked theories on the nature of consciousness—but would much rather hear yours.

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