By Stefanie Schneider
Blindsight: Sight Without Vision
If you close your eyes and someone waves their hand in front of your face, you wouldn’t be able to see it because your vision is blocked, right? Common sense tells us that if our vision is blocked or impaired, we’re not going to be able to know what is going on around us without additional assistance, but this is not actually true in all cases. Blindsight is essentially when someone with impairment in the primary visual cortex of the brain can identify the location of an object. The person acknowledges visual stimuli despite unconsciously perceiving them.
How Do We See?
A little bit of background information first: vision begins when light hits the retina. The information is sent by the optic nerve through the optic chiasm where the nerves cross. It is then sent to the primary visual cortex (V1), where the conscious action of vision/seeing occurs. The cortex then disperses the information for additional processing in more detail, which allows people to see the world around them.
History of Blindsight
Lawrence Weiskrantz, a British neuropsychologist, is known as the person who discovered blindsight. In 1974, he tested a patient at the National Hospital in London. The patient had had their primary visual cortex removed previously due to a tumor, so Weiskrantz and his colleagues tested his visual abilities. Previously, it was believed that without the V1 cortex, vision is completely cut off. To challenge this, the patient was asked to locate a stimulus or differentiate between two possible stimuli that could’ve been put out in front of him, using forced-choice guessing that had previously been used more for animal testing while human testing required more precise information from the test subject. The results showed that he was very successful in the tasks despite claiming he couldn’t see anything. Even though he couldn’t “see” his surroundings, he had “feelings” that led him to the correct interpretations. This brought forward the possibility that in the absence of connection with the V1, there were alternate methods for the brain to process the visual information from the retinas.
The term blindsight itself came from a seminar Weiskrantz gave to Oxford neurologists. In a rush to come up with a title for it, he named it “Blindsight and Hindsight”. The term blindsight was well received so it grew in use until it was officially added to the dictionary.
What Does This Mean?
In essence, blindsight indicates that the traditional pathway of visual information processed through the primary visual cortex is not the only way to view one’s surroundings. While it doesn’t mean that people who are considered legally blind that are missing their V1 cortex can miraculously see everything in detail, it does mean that the alternate visual processing pathways in the brain can allow people to detect some aspects of what is in front of them. More specifically, there are four main types of blindsight: action-blindsight, attention-blindsight, agnosopsia, and affective-blindsight.
Action-blindsight is when patients are able to follow objects in motion with their eyes or by pointing.
Attention-blindsight is when patients can sense items in their visual field without technically seeing them.
Agnosopsia is when patients can identify the color and shape of an object.
Affective-blindsight is when patients can identify facial expressions and body language.
While blindsight varies from person to person, as a whole, it is an astonishing way in which our body is able to create an element of vision despite being blind based on current definitions/categorizations.
Works Cited
Learning, Lumen. “Introduction to Psychology.” Lumen, courses.lumenlearning.com/waymaker-psychology/chapter/psych-in-real-life-consciousness-and-blindsight/. Accessed 7 Nov. 2023.
Weiskrantz, Larry. “Blindsight.” Scholarpedia, www.scholarpedia.org/article/Blindsight. Accessed 7 Nov. 2023.