By Barry Sandrew, Legend3D
This is not intended as an insult – it’s a legitimate suggestion because we all experience 3D movies differently, and many of us have vision problems that can affect the quality and way we experience 3D. We’re all aware of some film critics who have declared that they don’t like 3D movies in general or that the 3D in a particular movie is flat or the 3D adds nothing to the story. I would be interested in knowing if some of these critics have deficits in binocular vision that limit their appreciation of 3D if not their entire movie-going experience. An optometrist or ophthalmologist who is schooled in binocular vision can determine if a person has vision problems that prevent them from optimally seeing 3D movies. There are also some easy tests you can try online that can assess the quality of your 3D vision.
One Film Critic’s Generalisation about Hugo
I read an article the other day by an unnamed critic who wrote that Hugo causes eyestrain. It would have been more accurate if he had limited the statement to his own personal experience rather than generalising his reaction to the rest of the audience. Indeed, the film was nominated for 11 Oscars, so clearly many other viewers did not experience visual discomfort from the movie. It’s very possible that this critic is lacking something in his ability to comfortably watch a 3D movie. Most people who experience eyestrain in 3D movies are not stereo-blind. Their binocular vision can be normal during everyday activities and they can comfortably look at a stereogram or single 3D image, but they have difficulty in maintaining convergence and divergence of their eyes when watching a 3D movie.
That’s because a 3D movie requires our eyes to do something that does not happen routinely. In the real world, we focus and aim our two eyes (converge or diverge) at the same location in space. For instance, we have to both focus and converge on our thumb to see it in three dimensions. However, in a 3D movie, focus and vergence are completely separate. The only place in a 3D movie where anything is in focus is on the movie screen. However, independently of focus, the amount of disparity in an image pair signals the degree to which our eyes need to converge or diverge, providing the brain with an illusion of where an object is behind or in front of the screen respectively. How the brain and eyes try to reconcile this dissociation between focus and vergence is believed to cause discomfort in some people. However, this can often be treated through optometric vision therapy.
So we can’t really fault the critic for making the generalisation that Hugo causes eyestrain, because if he has a problem dealing with the special type of binocular vision required in a 3D movie, he is probably unaware of it and he likely thinks everyone is experiencing the movie in the same way as he. However, if he has his vision checked and, if necessary, gets professional treatment, it could potentially change his opinion of 3D movies and more importantly, he may start to appreciate the new medium and have a more fulfilling movie-going experience.
My Personal Experience with Partial Stereo Blindness
I’ve had personal experience with vision deficits that can create a less than optimal appreciation of 3D movies. When we were working on footage for Michael Jackson’s This is It Tour in the very early days of 2D to 3D conversion at Legend3D, I noticed that I was seeing things in 3D differently than my stereo artists. When they would comment how amazing a particular 3D converted shot looked, I could appreciate the stereo but not sufficiently to share in their excitement. I certainly was able to perceive 3D or I would not have been able to develop our software during the preceding two years. However, it wasn’t until we started to assess creative decisions as a team that it became most apparent I was missing something.
At that point, I decided to have my binocular vision checked by an ophthalmologist. What I learned was that I had been fitted with contact lenses using a corrective technique called ‘mono-vision’, where my left eye was corrected for seeing close and my dominant right eye was corrected for seeing far. This type of eye correction is very commonly used for nearsighted people. In essence, I was using only one eye for seeing far and one eye for seeing close. You might think that walking around like this is far worse than having just one good eye, but my brain adapted to the situation by partially ‘turning off’ or suppressing the blurry images coming from my non-dominant left eye when viewing something in the distance. I was still able to appreciate 3D movies and work in 2D to 3D conversion because I was forcing the use of my weaker eye but to a much a lesser extent than my dominant eye.
Children Have No Frame of Reference That They Might See the World Differently
This was not the first time I discovered that I had vision problems of which I was previously unaware. When I was in third grade, my teacher noticed that I was squinting at the blackboard and suggested to my parents that I have my eyes examined. The optometrist told me that I was nearsighted and needed glasses. Prior to this event, my parents never had my eyes tested, and I never doubted that I was seeing the world in the same way as all my friends. In other words, I had no frame of reference.
However, as soon as I was tested for glasses I was amazed at how clear and sharp the world really was, and I recognised how much I was missing. Indeed, the same was true of my 3D vision. As soon as the doctor changed my prescription so that my eyes were perfectly balanced for seeing distance with a correction greater than 20/20, my perception of 3D vastly improved, and I developed acuity for 3D that today very often exceeds that of my colleagues. I now have to wear glasses for reading, but my distance and binocular vision is exceptionally sharp. This clearly elucidated to me the fact that that no two people see 3D movies in quite the same way.
Convergence Problems and Stereo-blindness
My eye condition is one of the most common visual anomalies that have the potential of dampening the perception of 3D movies. More extreme conditions are found in people with strabismus (crossed eyes or wall-eyes) who cannot experience 3D vision because each eye is seeing a perspective so different that the brain cannot fuse the two images into a single 3D image. As a consequence, people with this neurological condition depend on only one eye to see the world, rendering them truly stereo-blind. These people literally exist in a flat visual world with little if any sense of depth and volume.
Stereo Sue: One Neuroscientist’s Journey into the 3D World
A well-known neuroscientist, Dr. Sue Barry suffered from a congenital form of crossed eyes, but like my experience in third grade, she thought everyone saw the world the way she did. However, as a junior in college, she attended a neurobiology lecture where experiments were described in which kittens with experimentally-created strabismus were found to lack the binocular neurons thought to be necessary for 3D vision. There appeared to be a critical period in the development of the brain during which experiencing binocular vision is essential for the development of stereopsis or 3D vision. It was only then that Dr. Barry realised that she was no different to those kittens and was very possibly permanently stereo-blind, never having seen the world in three dimensions.
As a child, she had undergone three surgeries to adjust the muscles in her eyes so her gaze would become straight. Unfortunately however, the outcome was more cosmetic than curative. To see in 3D in the real world, you have to point your two eyes at the same place in space, at the same time. While the surgery may have put her eyes into better alignment, it did not teach her how to aim her two eyes simultaneously at the same spatial location. When she had to focus on something, instead of her two eyes equally converging inward on an object, one eye would look straight at the object and the other would turn in. She could never adjust her eyes so that images of objects would fall on the same corresponding place on her two retinas. Therefore, fusion in her brain of the two perspectives into a single 3D image was impossible.
Rewiring the Brain to See 3D
At the age of 48, Dr. Barry consulted a developmental optometrist who guided her through a programme of optometric vision therapy that taught her how to point her two eyes simultaneously at the same point in space and fuse within her brain the images falling on her two eyes. What is so fascinating is that over time she was able to rewire her brain to fully experience 3D.
While this is an anecdotal example, there are other cases like Dr. Barry’s documented in the optometric literature. These cases contradict the cat study mentioned above as well as conventional wisdom in neuroscience that there is a critical time in an infant’s development where the absence of stereopsis creates stereo-blindness. In the case of Sue Barry, her congenital condition of strabismus prevented her from seeing the world in three dimensions from birth. Her poignant introspective journey into this foreign 3D world and how it changed her life is fascinating. I invite my readers to pick up her book, Fixing My Gaze, A Scientist’s Journey into Seeing in Three Dimensions. One of the many examples of the wonders she experienced in this new world is her description of seeing snow falling in three dimensions for the first time rather than the way she saw it all her life as a flat sheet of various sized white dots falling in front of her.
Today, one of her favourite pastimes is going to 3D movies, and she recently told me that she particularly enjoyed Hugo. She also told me that while she has always enjoyed 2D movies, after gaining binocular vision she now experiences them differently. Because of her new, real world experience of seeing in stereo, her brain can now ‘fill in’ the stereo depth in a 2D movie that is suggested by monocular cues such as object occlusion and motion parallax. People who have always had stereopsis have this innate ability to ‘fill in’ stereo depth in 2D images. However, you cannot experience a sense of depth and volume in a 2D movie if you’ve never experienced that sense of depth and volume in real life. We take these things for granted so it never occurred to me that while still stereo-blind, Dr. Barry did not experience a 2D movie the way people with normal vision do.
The passion with which she describes the immersive qualities of her new found 3D existence is one of the best, real-world examples of the importance of binocular vision to our quality of life, and it points to the relative difference of being engaged in a 2D movie or immersed in a 3D movie.
Everyone in the business of storytelling using 3D should have his or her eyes examined for binocular vision. Correctly experiencing 3D movies requires two eyes that are balanced for focusing images on the movie screen, and the ability of specialised parts of the brain, tuned to disparity to fuse the two images on the screen into a single 3D image, giving the impression of depth and volume.
If there are deficits in 3D vision they should be corrected so that both eyes are 20/20, or at least evenly balanced, to reduce eye dominance. If the separation of focus and vergence causes eyestrain, then optometric vision therapy might be the answer. As 3D becomes ubiquitous, people with 3D home theatres and those that enjoy the 3D theatre-going experience should have their binocular vision checked as a matter of course on their next visit to the eye doctor.
This article is based on a blog from the series of ‘Reflections on the Growth of 3D‘ by Barry Sandrew Ph.D., Founder and CCO/CTO of Legend3D. Legend3D is a leading digital media technology company that specialises in 2D-to-3D conversion.