Stereo Sue, Susan Barry and Stereoscopic Vision

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What Is Stereoscopic Vision?

Stereoscopic vision or seeing in stereo refers to seeing in 3D or 3 dimensions. If you have binocular vision, your eyes coordinate with the brain. Each eye sends an image so that the brain can merge them into one image in 3 dimensions, i.e., with depth.

One person out of every 20 does not see in three dimensions. This means they do not have a stereoscopic vision and see the world as flat, two-dimensional. Since this vision is not binocular, it does not come from both eyes but from one at a time (monocular vision).

In order to have a vision in three dimensions, the two retinas of the eyes must have slightly different perspectives of the same object so that the brain fuses these two complementary images to form depth vision.

When these two complementary images derived from each of the retinas are very different, the brain cannot fuse them, and it suppresses one of them, forcing us to see in two dimensions without depth perception.

Despite this, many people who cannot see the world in depth or 3D can function adequately in their environment.

They have learned to adapt to a ‘sensation of depth’ through monocular signals, such as shadows or lights that produce effects on the objects they observe, the proximity or remoteness of objects based on their size, or when one object covers another. They know that the more distant one is entirely covered by the nearby one.

When vision is in two dimensions, the visual process is slower, inefficient, and confusing. It is not easy to perceive the distance and space between objects.

Stereoscopic vision enables us to better calculate the distances between these objects and the position between them and perceive the space between them.

When we refer to strabismus or amblyopia, the brain cannot correctly coordinate the images each eye provides since the two eyes do not work together, making stereopsis impossible.

The aim is to train the brain, to re-educate it to adequately coordinate the two images and form a single image, thus achieving a stereoscopic vision.

However, as Oliver Sacks indicated in his article Stereo Sue, it was not until 1840 that the English inventor and scientist Charles Wheatstone (1802 – 1875) began to suspect that the differences between the images provided by each eye had something to do with the ability to have the sensation of depth emitted by the brain.

To do this he performed an experiment: he made two drawings of the same solid object from different perspectives, just as each eye would do, and then, with the help of an instrument he designed called a stereoscope (from the Greek ‘for solid vision’) He had two mirrors, which ensured that each eye saw its own drawing in the same way as each eye would.

When looking into the stereoscope, the two flat drawings were merged, and a single three-dimensional drawing was created.

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Who is Susan Barry?

Susan Barry was born on February 20, 1954, to an artist father and a history teacher mother. The prologue of the book ‘Strabismus and lazy eye’ by Pilar Vergara states that Susan had strabismus since she was a child and underwent three surgeries to align her eyes. Still, they did not allow her to improve her vision.

She only had a 3D vision when she was 47 after beginning optometric vision therapy in 2001 with Dr. Theresa Ruggiero.

One of the exercises she first practiced was with Brock’s String, which allowed her to learn to merge the two images she received from each eye, without suppressing one.

She learned to direct her eyes toward the same point thanks to her perseverance, effort, hard work, and motivation. This way, she could see the space between objects for the first time and ‘see’ the world with a three-dimensional vision.

But who better than she herself to tell us her story:

No supo que no veía en tres dimensiones hasta los 20 años, mientras asistía a una clase de neurobiología, cuando le explicaron en la facultad, que las personas que sufrían de estrabismo, no podían disponer de visión estereoscópica.

Susan Barry se licenció en Biología en 1976 en la Universidad Wesleyan, Connecticut y se doctoró en Biología en la Universidad de Princeton en 1981. 

Trabajó como neurocientífica investigadora en la Facultad de Medicina de la Universidad de Miami (Florida), la Universidad de Michigan en Ann Arbor, en el Centro Espacial Johnson de la Nasa en Houston (Texas) y en el Laboratorio de Biología Marina en Woods Hole, Massachusetts. 

Además, fue profesora de neurobiología en el Departamento de Ciencias Biológicas en la Universidad Mount Holyoke College (Massachusetts, Estados Unidos) desde 1992 hasta 2016, momento en el que se retiró.

La Dra. Barry es una reconocida autoridad en el campo de la plasticidad sináptica de las neuronas gracias a sus investigaciones y su vinculación con la comunidad científica de la neurobiología. Conocida en Estados Unidos como ‘Stereo Sue’.

Fixing My Gaze, Book Written By Susan Barry

In 2009, Dr. Susan R. Barry published her book “Fixing my gaze: A Scientist’s Journey Into Seeing in Three Dimensions.”

In it, Susan Barry herself is the protagonist and shows us in first person how visual stimuli are processed until they reach the brain when a person does not have a stereoscopic vision and the discovery of finally being able to have it.

In her book, Dr. Barry allows us to accompany her through the journey towards a stereoscopic vision, undoubtedly a revealing work in the field of neuro-rehabilitation.

Seeing in Stereo by Susan Barry, published in 2009, was the fourth book among the Top 10 best scientific books according to Amazon.

Below, we can find a lecture in English where Susan Barry herself comments on the contents of her book ‘Fixing my gaze’.

Stereo Sue

Until recently, it was believed that the ability to have stereo vision developed only in childhood.

The brain is wired so that seeing in three dimensions requires similar images to provide a unified 3d image. Suppose each eye points in a different direction. In that case, the brain cannot coordinate the two images, so it discards one of them, and the neural circuits are modified accordingly.

It was believed that these changes in the neurological pathways, which happen between 2 to 4 months of age, were permanent. However, through vision therapy, it is possible to learn to focus both eyes on the same point.

As we see in Dr. Susan Barry’s case, we can change the visual habits we have adopted since childhood. Her experience suggests that the brain has enough plasticity for the binocular cells and circuits to be activated in the brain.

In June 2006, Dr. Oliver Sacks published an article in The New Yorker about her case and titled it Stereo Sue, hence her nickname Stereo Sue.

Since that article, she was inspired to continue researching binocular vision and vision therapy and eventually write her book.

As shown in his article, Dr. Sacks also discusses the experience of Paul Romano, a pediatric ophthalmologist who lost binocular vision for an extended time after an ocular hemorrhage.

Dr. Romano expresses what he experienced during the period of experiencing two-dimensional vision: ‘Things are not the same object, monocular as they are binocular’ ‘Binocular stereoscopic depth perception is not just a visual phenomenon.

It is a way of life. Life in a two-dimensional world is very different from that in a three-dimensional world and much inferior’.

If you still need to read the full article Stereo Sue by Oliver Sacks, please feel free to read it here.

Below, we find a short interview where Oliver Sacks, author of the book ‘The Mind’s Eye‘ shows us the case of Stereo Sue in a video where both appear:

Eduard Punset Interviews Susan Barry In 'Redes'

Interview Of Eduard Punset With Susan Barry In ‘Redes’
To finish this article we would like to do it with the transcript and recording of the interview conducted by Eduard Punset in his popular science program Networks in chapter number 99 issued on June 12, 2011, on TV2, entitled: ‘See the World in stereo’.

This interview conducted by Punset with Dr. Barry gives us an overall idea of everything we have discussed throughout our article. We hope you enjoy it:

“When we look at a close object against a more distant background, we are able to perceive the space in between.

However, one in twenty people sees the world as if it were flat. Many are not even aware of their deficiency, but, with the right therapy, they can manage to see the world in three dimensions.

Susan Barry, neuroscientist and author of the book The World in Stereo, was one such person. In this episode of Redes, the author explains to Eduard Punset the wonders of stereoscopic vision.

We have two eyes, but only one view of the world. Susan Barry

Eduard Punset: Susan, finally, can we talk about your wonderful experience that started when you were, what, forty years old?

Susan Barry: Forty-eight years old.

Eduard Punset: Forty-eight years old. Until then, you saw the world as flat.

Susan Barry: That’s right.

Eduard Punset: So when you see Dan, your husband, who is an astronaut, well, who was an astronaut, catapulted into space, even something so moving is nothing compared to being able to see the world for the first time in its stereoscopic depth.

Is it so different to see things flat, you say flowers are flat, to seeing them in depth?

Susan Barry: Absolutely, it gives you a qualitative way of seeing the world. Imagine you had never seen the color red and suddenly one day, one day in autumn, when all the trees are showing their beautiful foliage, with all those wonderful colors, you see the color red for the first time. Could you stop looking at it?

Eduard Punset: Maybe not.

Susan Barry: Well, it’s very much like the experience I had. I had a sense of space, palpable volumes of space, pockets of space between things, and although I could infer it before my vision changed, I knew that the world existed in-depth, although I didn’t see it that way.

So it was an eye-opening experience.

The Brain Merges Everything
Eduard Punset: Please correct me if I’m wrong, but it seems that with each retina, you see something different, something slightly different, and the brain fuses it all together so that you can have that depth perspective. Is that true?

Susan Barry: Well, since the 1950s, the conventional wisdom has been that you have to develop the ability to have stereoscopic vision, to see things in three dimensions within the first few years of life, sometime in early childhood.

And if you don’t develop it at that age, your brain is wired in such a way that you will never be able to see in three dimensions; but why would the brain do that? Let’s see, if it had one eye looking at you and the other eye looking away, they would have very different views of the world, so you would see everything duplicated, and you wouldn’t know where things were.

You would have to choose one of the two eyes, so the brain chooses one eye and ignores or eliminates the information it receives from the other. So the brain circuits are modified accordingly.

It was thought that these changes were permanent, but they are not. With proper therapy, many cross-eyed people can learn to do what I did.

The Brain And Its Areas
Eduard Punset: When you say, or when you talk about the brain, what are the areas that, in fact, manipulate everything?

I mean, those areas that when they are activated, they sort of modulate things, dopamine or whatever, so that you end up seeing in three dimensions, you end up having a stereoscopic vision.

Susan Barry: Okay. There are a lot of brain areas that are involved. We start with the eye and the retina in the back of the eye. Did you know that the retina is actually a part of the brain?

It’s actually brain tissue. It communicates with different synaptic junctions, with the visual cortex, which is at the back of the brain and that is where the images from both eyes are first fused, that is, there are neurons there that capture information from both eyes at the same time.

Eduard Punset: So what you are telling me is that from the back of the brain, we start to evaluate that there are two slightly different visions and we start to merge those visions?

Susan Barry: That’s right. From the back. And that information diffuses to many other areas of the brain, some of which have to do with the shape of objects, some of which have to do with the location of those objects in space and our own spatial position that allows us to grasp and manipulate those objects.

So that ability to fuse information from both eyes is used over and over again in the brain in order to recognize objects and to know where things are.

Eduard Punset: That’s probably what we have learned from you neurologists, is what you call personal experience or individual experience, which can influence the structure of the brain. You call it “plasticity,” I think.

Susan Barry: Plasticity, yes, neuroplasticity.

Eduard Punset: Yes, and how is it possible that with neuroplasticity, with neuroplasticity existing, how is it possible that the human brain does not accept any change since childhood?

Susan Barry: Well, here’s the situation: when I was little, let’s say when I was two or three months old, I crossed my eyes; if I looked with one eye, the other eye was turned inward, and what I saw was different. From four months on, babies start to want to reach for objects, to want to grab things.

But if your two eyes are looking in different directions at the same time, it’s going to be hard for you to know where things are. You’re going to get two different images: one coming from your right eye and one coming from your left eye, and they’re too different for the brain to merge them into a single point, so you have to learn to suppress one eye, and one of the ways to suppress one eye is to divert it even more.

So throughout my life, I have learned to look with one eye and divert the other eye inward, to ignore what I saw. Notice that thanks to that, I was able to grasp objects when I was four months old and try to pick things up.

At one year of age, our visual habits and the way we use our eyes are consolidated, and we have a way of waking up in our environment.

So, to change at forty-eight years old, I had to break some visual habits that had been with me for forty-eight years and learn something new: to learn to focus both eyes on the same point at the same time.

So it had to be very conscious exercises. The therapy had to teach me where my two eyes were looking in order to learn to change that direction and direct both eyes to the same point at the same time.

And I had to be very conscious of what I was doing. I had to practice every day. It was not a spontaneous change, it had to come with practice.

Eduard Punset: Well, I guess that was the price you had to pay for not seeing flowers in two dimensions.

Susan Barry: Right, to be able to see them coming closer to you, to be able to see each leaf and petal in a different space.

What optometric vision therapy taught me was how to focus both eyes on the same point. That’s how I started to perceive the depth of things.

Vision And Animals
Eduard Punset: Listen, there is something that fascinates me. It seems that all this stereoscopic vision, which you learned after forty years, is something extremely useful for some animals.

Well, and for humans of course, but apparently there are cuttlefish, gibbons, that go from one branch to another, that would fall to the ground if they couldn’t see in three dimensions, right?

And in order to see the world in stereo, the eyes of some organisms look frontally like this, right? They don’t see anything behind, and they don’t have a panoramic view. Is that right? Is it essential for us, like for gibbons, to have that stereoscopic vision?

Susan Barry: Yes, probably because our ancestors were tree-dwelling animals. It’s very important, when we climb a tree, to have stereoscopic vision.

Think of a child who has to climb on the gymnastic apparatus or who goes from one branch to another or swings from one branch to another. It is very useful to have that depth perception to know where the other branches are in space.

In general, it’s believed that predators that chase and grab other animals, whether it’s a praying mantis or a squid as it grabs its prey, tend to have eyes that allow them to look straight ahead.

And they have stereoscopic vision. Animals that are prey that are the ones that have to flee, the ones that are going to be devoured, tend to have their eyes positioned more to the sides of their head to have a wider view of everything around them so they can escape.

This would explain in general, why some animals have two eyes that look frontally and stereoscopic vision and others have more lateral eyes and a more panoramic vision.

The Eyes And The Brain
Eduard Punset: At the beginning, it seems, we discovered, some scientists discovered, I think it was Galen, in the second century A.D., that each eye had a different vision, right?

Susan Barry: Yes.

Eduard Punset: But nobody knew why the hell…, what was the purpose…., they didn’t understand that the brain was acting mysteriously, merging the two visions, and we had to wait until the 18th century, I think, with a scientist named…

Susan Barry: Until 1838.

Eduard Punset: 1838? What was his name, Wheatstone?

Susan Barry: Charles Wheatstone.

Eduard Punset: That. Actually, what did he discover?

Susan Barry: Let’s see, here’s the thing: let’s imagine you hold up your finger like this, in front of you. You close one eye and then the other. You perceive as if your finger jumps slightly. It’s because our two eyes are somewhat separated on the face, so they have a somewhat different view of the world.

And it’s that somewhat different view of the world that our brain is able to process and combine to have that three-dimensional sensation.

For a long time, people believed that the fact that the two eyes saw something slightly different was a defect. And Wheatstone, Charles Wheatstone, was the first to say that, no, not at all, that this is what allows us to have that stereoscopic depth sensation.

And he proved it by building the first stereoscope. With the stereoscope, each eye saw a different image, but the image would be equivalent to the perspective from which each eye looked. That is, let’s imagine that I wanted to look at a chair, one eye would see the chair from its perspective, and the other eye would see the chair from its perspective as well.

Then the brain would say, “Oh, I’ve used these images and combined them,” so even though each eye would see a flat image of the chair, when you looked through the stereoscope with both eyes, the brain would have combined them and, you could see the chair as if it were in three dimensions.

That’s how three-dimensional movies and three-dimensional toys work, each eye has a slightly different view, and the brain combines them to give them stereoscopic depth.

The Shortcomings of Flat Vision
Eduard Punset: Susan, can there be anyone in our audience…? It has occurred to me in a program that we dedicate to synesthesia… I mean, could there be someone in our audience who does not see the world in the right way, who sees flat flowers and is not aware even today that he or she could see the world in three dimensions?

Susan Barry: Absolutely. About one in twenty people do not see in three dimensions.

Eduard Punset: One out of twenty?

Susan Barry: That’s right, maybe it’s because they have been cross-eyed, like me, or strabismic, that is, they have strabismus, which means that one eye looks one way and the other eye either looks inward, in which case we are talking about a cross-eyed person, or looks outward, strabismic.

Or they may have another more subtle visual problem that prevents them from having a stereoscopic vision.

It’s a very common thing. The interesting thing is that if you try to close one eye, a lot of people say to me, “Sue, I don’t know what you’re talking about. If I close one eye, the world doesn’t look very different.”

This is the feeling of many people, but if they have always had binocular vision, stereoscopic vision, throughout their whole life, no matter how much they close one eye, they will not perceive in the same way as I did before because their brains take advantage of a lifetime of stereoscopic experiences to provide the missing information.

So, first, you have to lose vision in one eye for a certain period of time to realize how different it is to see the world without depth. I discovered this in an interesting way. It was by going to the cinema, watching a two-dimensional movie, not a three-dimensional movie.

Eduard Punset: In two dimensions.

Susan Barry: A two-dimensional movie. Cinematographers, the people who make movies, are very clever at using all kinds of cues: motion cues and other kinds of cues to give us a sense of volume and space.

Shortly after my vision changed, my husband and I decided to go see the latest installment of the Star Wars movie on opening night. This was two years after my eyesight began to change.

And as I was watching it, as I watched the spaceships moving and floating through space on a flat movie screen, I thought, wow!!! How cinema has changed since I saw the last episode of the Star Wars saga! There was so much more space and volume.

It wasn’t until the next day, after a good night’s sleep, that I realized that this movie was not so different from the last Star Wars…

Eduard Punset: From the last Star Wars…

Susan Barry: Having experienced that sense of space and volume in real life, I was able to see it in the movie as well, and that helped me realize why when people close one eye, they may not know the difference.

It’s because they have accumulated stereoscopic experiences over a lifetime, which can fill in that missing information.”

To view the full video, click on the following link:

It is also possible to view the recording of the interview in its original version in English and without subtitles here.

In addition, Eduard Punset wrote the introduction for the Spanish edition of Susan Barry’s book ‘Ver en stereo’ and indicates that: “No one has explained with Susan’s clarity the long process to correct her birth strabismus, more common than suspected. She has demonstrated that this almost innate learning to see in 2D can be corrected if we employ the right therapy.”

Excerpted from the website of optometrist and former director of the International Society for Developmental and Behavioral Optometry SIODEC Elisa Aribau.