Binocular vision refers to the ability of eyes to work together to perceive depth and create a single, three-dimensional image. It plays a critical role in spatial perception, allowing us to judge distances and navigate our surrounding environment. This is achieved through a process known as stereo vision, in which each eye receives a slightly different image of the same scene. The brain then combines these two images to create a single, more detailed image with a sense of depth and distance. The eyes are positioned slightly apart from one another, which allows each eye to see a slightly different angle of the same object. This slight difference in angle is known as binocular disparity, and it is this difference that allows the brain to perceive depth.
This image demonstrates the binocular visual field. The ‘Left Eye View’ and ‘Right Eye View’ indicate a monocular visual field (https://www.scientificamerican.com/article/exploring-the-depths-of-vision/Credit:George Retseck)
The study of visual binocularity, or the ability to use both eyes together to perceive depth and spatial relationships, has a long history dating back to the early 19th century. One of the earliest researchers in this field was the German physiologist Franz Joseph Gall, who proposed the theory of phrenology, which claimed that the shape of the skull could reveal a person's mental abilities and characteristics. In the mid-19th century, British physician Sir Charles Bell and French physiologist Louis Pierre Gratiolet independently discovered the concept of binocular disparity, which is the slight difference in the images that each eye sees. This difference is used by the brain to perceive depth and distance. In the late 19th and early 20th centuries, the psychologist and philosopher Ernst Mach, and physiologist and psychologist Sir David Brewster, made important contributions to the understanding of binocular vision and stereopsis (the perception of depth from the combination of the slightly different images from each eye).
In the 20th century, David Hubel and Torsten Wiesel discovered the importance of the primary visual cortex in binocular vision and showed that neurons in this area respond selectively to binocular disparities.
Apart from mammals, birds also possess visual binocularity, and this trait is thought to be important for their survival as it allows them to accurately judge distances and navigate while flying. Most fish, on the other hand, have greater monocular vision and much less visual binocularity as their eyes are located on either side of their head. This allows them to have a wide field of view but they are not able to judge distances as accurately as mammals or birds. Insects also have lesser visual binocularity. They have compound eyes which consist of many smaller units called ommatidia giving them a wide field of view but poor distance or depth perception.
Binocular vision disorders occur when there are problems with the way the eyes work together as a team. This can cause issues with depth perception, eye strain, and headaches. Some common binocular vision disorders include:
Strabismus: eyes that are misaligned, pointing in different directions.
Amblyopia: a decrease in vision in one eye due to the brain ignoring input from that eye.
Convergence Insufficiency: difficulty focusing both eyes on near objects, leading to eye strain and headache.
Diplopia: double vision caused by misaligned eyes or muscle weakness.
These disorders can be treated with various methods, such as eye exercises, vision therapy, and/or glasses or contact lenses and in severe cases, even surgery might be necessary.
Today, research in the field of visual binocularity continues to advance our understanding of the neural mechanisms underlying binocular vision and the perception of depth and has practical applications in fields such as ophthalmology, robotics and virtual reality.
1. Signs and Symptoms of Binocular Vision Problems. Available from: https://www.seevividly.com/info/Binocular_Vision/Signs_and_Symptoms
2. Howard, Ian P., and Brian J. Rogers, 'Binocular and stereoscopic vision in animals', Binocular Vision and Stereopsis, Oxford Psychology Series (New York, 1996; online edn, Oxford Academic, 1 Jan. 2008), https://doi.org/10.1093/acprof:oso/9780195084764.003.0016
3. Finger S, Franz Joseph Gall and the Origins of Phrenology (26 July, 2019). Available from: https://becker.wustl.edu/news/franz-joseph-gall-and-the-origins-of-phrenology/
4. Wade NJ. On the Origins of Terms in Binocular Vision. Iperception. 2021 Feb 24;12(1):2041669521992381. doi: 10.1177/2041669521992381. PMID: 33717428; PMCID: PMC7926055.
5. Lienhard, Dina A., "David H. Hubel and Torsten N. Wiesel’s Research on Optical Development in Kittens". Embryo Project Encyclopedia (2017-10-11). ISSN: 1940-5030 http://embryo.asu.edu/handle/10776/12995.Available from: https://embryo.asu.edu/pages/david-h-hubel-and-torsten-n-wiesels-research-optical-development-kittens
About the author
Author: Aiendrila Roy
Editor: Maalavika Govindarajan