His eyes are working well, they are intact. But they say they don’t see anything. And they really see, not knowing what they are seeing. This curious phenomenon is what happens to people who suffer from blind vision, a neurological disorder caused by brain damage that affects the ability to consciously represent visual stimuli from the environment.
In this article, we explain what blind vision is, how this concept appears, what are its causes, and how to differentiate it from other similar disorders.
Blind vision: definition and context
Blindsight is a term coined by the English psychologist Lawrence Weiskrantz, which alludes to the ability of certain subjects to unconsciously detect, locate and discriminate visual stimuli. People who suffer from this disorder “see, not knowing that they are seeing”; that is, they do not consciously recognize the objects in front of them, even if they act as if, de facto, they are there.
The first investigations into the phenomenon of blind vision were carried out in animals, mainly monkeys, with surgical removal of the brain regions responsible for vision (zone V1). When deprived of these structures, animals seem to retain certain visual abilities, such as the ability to sense contrast or differentiate one object from another based on its shape.
Few neuroscientists believed humans could have normal vision with these damaged areas of the brain. Patients whose visual cortex had been destroyed showed complete blindness, at least at least. In 1973, the team of German psychologist Ernst Poppel found that although some of them did not have a visual cortex and reported that they were unable to see objects, the eye movements of his eyes were directed towards them: It was the proof that his visual system informed, in a certain way, of their existence.
But what has just convinced the scientific community that the phenomenon of blind vision deserves all its attention is the work of Larry Weiskrantz and his colleagues in the early 1970s. The forced choice technique was used in experiments (Force patients to choose from defined options, rather than just asking what they see): Patients were asked to choose between two possible colors or locations, while being asked to guess which one was applicable to a visual object. That they said they couldn’t see.
Responses from some patients were found to be significantly correct; that is, with a higher frequency than one might expect by chance. It was from there that these people started to be labeled as blind patients.
At present, it has been shown that blind people they can not only “intuitively” the color or location of objects, but also the orientation of lines or grids, time of appearance or facial expressions.. However, they cannot do this with other aspects such as detecting subtle nuances or complex movements.
Causes and brain structures involved
Blind vision occurs in a part of our perceptual organs: the scotoma or blind spot. This phenomenon occurs in the event of lesion or injury of the occipital lobe, and more particularly of the primary visual cortex (V1)., Who is responsible for processing visual stimuli.
When we receive information about an object through the retina of our eyes, it moves from the optic nerve ganglion cells to various subcortical structures which, acting as areas of relief, are responsible for integrating information from each modality. sensory (in this case, sight).
At the subcortical level, visual information passes through structures such as the medulla oblongata, midbrain, and the lateral geniculate nucleus of the thalamus. At this level, we are not yet aware of what we have “seen”As the information has not yet reached the upper cortical levels. However, it can influence our behavior, as in the case of blind vision, in which the person sees, without knowing what he is seeing.
Visually impaired patients have therefore damaged the final modulus of a complex visual processing circuit, which is insufficient on its own and without the other sensory and subcortical structures but necessary, at the same time, for there to be conscious recognition. of what we perceive. .
The sensorimotor vision model
The conventional model of structural failure in visual processing (involving injury to various areas of the brain) implicitly assumes that vision is to create an internal representation of external reality, activation would generate a conscious visual experience. However, this is not the only one that has been postulated in an attempt to explain why a phenomenon such as blind vision occurs.
The ecological approach to visual perception proposed by psychologist James J. Gibson, Believes that vision should be understood as a necessary tool for survival. According to Gibson, the real value of visual processing is being able to identify and see with our gaze what is there and where, so that we can avoid obstacles, identify possible food or threats, achieve goals, etc.
All of this “visual deduction” work would be done by the retina interacting with multiple environmental cues. And the key would be in discriminate the relevant information, from so many signals, to be able to manage a particular behavior.
Today, the Gibson approach has been reformulated as the sensorimotor model of vision, in which the concepts of the ecological approach are borrowed and it is postulated that vision is an activity of exploring our environment based on sensorimotor contingencies, not a representation that we have created internally.
What does it mean? what vision is not just about receiving information through our eyes; this information is modeled and transformed based on the motor (eg, eye muscles or pupillary contraction) and sensory changes that accompany this visual experience, as well as the visual attributes of the objects we perceive for ourselves.
The fundamental difference between the sensorimotor model and the conventional model is that the latter assumes that if a certain region of the brain (the primary visual cortex) fails or is necessary, the internal representation disappears from conscious perception, which implies; on the contrary, by the sensorimotor approach, the external world would not be retained in the mind of the person who perceives it and reality would function as an external memory tested in the relations between sensory stimuli and motor responses.
When diagnosed, blind vision should be differentiated from another set of similar disorders such as double hemianopsia, Munk’s mental blindness, hysterical blindness, and sham blindness.
The patient maintained macular and central vision, Although he has a vision in the form of “gun barrel”. This disorder can precede or follow blind vision.
Munk’s psychic blindness
The person has difficulty recognizing objects (visual agnosia), although they do retains the feeling of visual awareness.
The patient is indifferent, but without anosognosia. Tests confirm that vision is normal, even if the person reports partial or total vision problems.
The person invents his own evil, In this case, blindness, to assume the role of patient (Münchhausen syndrome)
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- Brogaard, B. (2011). There are unconscious perception processes. Consciousness and Cognition, 20, 449-463.
- O’Reagan, J. and Noë, A. (2001). A sensorimotor narrative of vision and visual awareness. Behavioral and Brian Sciences, 24, 939 – 973.