Blind vision: causes and symptoms of ’seeing without knowing you see’.

This neurological disorder causes some people to see despite believing they are totally blind.

Their eyes work fine, they are intact. But they say they don't see anything. And they really see, without knowing that they see. This curious phenomenon is what happens to people who suffer from blind vision, a neurological disorder. blind vision, a neurological disorder caused by brain damage caused by brain damage that affects the ability to consciously represent the visual stimuli of the environment.

In this article we explain what blindsight is, how this concept arises, what its causes are, and how to differentiate it from other similar disorders.

Blind vision: definition and background

Blind vision (blindsight) is a term coined by the English psychologist Lawrence Weiskrantz, which refers to the ability of some subjects to detect, locate and discriminate visual stimuli unconsciously. People suffering from this disorder "see, without knowing that they see"; i.e., they do not consciously recognize that they see.that is, they do not consciously recognize the objects in front of them, even though they act as if they were, in fact, there.

The first research on the phenomenon of blindsight was carried out on animals, mainly monkeys, with the surgical removal of the brain regions responsible for vision (area V1). When deprived of these structures, the animals seemed to retain some visual abilities, such as the ability to detect contrast or to differentiate one object from another based on its shape.

Few neuroscientists believed that humans could achieve normal vision with these damaged brain areas. Patients whose visual cortex had been destroyed showed total blindness, or so it seemed. In 1973, the team of German psychologist Ernst Pöppel found that, although some of them lacked visual cortex and reported that they were unable to see objects, the ocular movements of their eyes were directed towards them.This was evidence that their visual system was somehow informing them of their existence.

But it was the work of Larry Weiskrantz and his colleagues in the early 1970s that finally convinced the scientific community that the phenomenon of blindsight deserved its full attention. The experiments used the forced-choice technique (forcing patients to choose between defined options, rather than just asking what they see): patients had to choose between two possible colors or locations, while being asked to guess which one applied to a visual object they said they could not see.

The answers of some of the patients turned out to be correct in a significant proportion; that is, with a higher frequency than would be expected by chance. It was thereafter that these people began to be labeled as patients with blindsight.

Today, it has been shown that people who are visually impaired can not only "intuit can not only "sense" the color or location of objects, but also the orientation of lines or grids, the time of appearance or the expressions of faces.. However, they cannot do so with other aspects such as the detection of subtle nuances or complex movements.

Causes and brain structures involved

Blind vision occurs in a portion of our perceptual organs: the scotoma or blind spot. This phenomenon occurs when there is damage or lesion in the occipital lobe, and more specifically in the primary visual cortex (V1), which is responsible for processing visual stimuli.which is in charge of processing visual stimuli.

When we receive information about an object through the retinas of our eyes, this information travels from the ganglion cells of the optic nerve to various subcortical structures that, acting as relay zones, are responsible for integrating the information from each sensory modality (in this case, vision).

At the subcortical level, visual information passes through structures such as the medulla oblongata, the midbrain and the lateral geniculate nucleus of the thalamus. At this level, we are not yet aware of what we have "seen".This is because the information has not yet reached the higher cortical levels. However, it can influence our behavior, as occurs in cases of blind vision, in which the person sees without knowing that he or she sees.

Blind vision patients have therefore damaged the final module of a complex visual processing circuit, which is insufficient by itself and without the rest of sensory and subcortical structures but necessary, at the same time, for there to be a conscious recognition of what we perceive.

The sensorimotor model of vision

The conventional model of structural failure in visual processing (involving a lesion in several areas of the brain) implicitly assumes that vision consists of creating an internal representation of external reality, the activation of which would generate the conscious visual experience. However, it is not the only one that has been postulated to try to explain why a phenomenon such as blindsight occurs.

The ecological approach to visual perception, proposed by the psychologist James J. Gibsonconsiders that vision is to be understood as a necessary tool for survival. According to Gibson, the real value of visual processing lies in being able to identify and see with our eyes what is there and where, so that we can avoid obstacles, identify food or possible threats, reach goals, etc.

All this work of "visual deduction" would be done by the retina in interaction with multiple environmental signals. And the key would be to discriminate the relevant information, among so many signals, to be able to manage a particular behavior..

Today, Gibson's approach has been reformulated as the sensorimotor model of vision, which borrows concepts from the ecological approach and postulates that vision is an activity to explore our environment based on sensorimotor contingencies, not a representation that we create internally.

What does this mean? That vision does not imply only the reception of information through our eyes; that information is shaped and shaped by our own eyes.That information is shaped and transformed by the motor (e.g., eye muscles or pupillary contraction) and sensory changes that accompany that visual experience, as well as by the visual attributes of the objects we perceive themselves.

The basic difference between the sensorimotor model and the conventional model is that the latter assumes that if a certain brain region (the primary visual cortex) fails or is missing, the internal representation disappears from conscious perception, with all that this implies; on the contrary, for the sensorimotor approach, the external world would not be remembered in the mind of the person who perceives it and reality would function as an external memory that is tested in the relationships between sensory stimuli and motor responses.

Differential diagnosis

When it comes to diagnosis, blindsight must be differentiated from a number of other similar disorders such as double hemianopsia, Munk's psychic blindness, hysterical blindness, and simulated blindness.

Double hemianopsia

The patient has preserved macular and central visionThe patient has preserved macular and central vision, although he has "gun-barrel" vision. This disorder may precede or follow blindsight.

Munk's psychic blindness

The person has difficulty recognizing objects (visual agnosia), although he/she retains a sense of visual awareness. retains a sense of visual awareness.

Hysterical blindness

The patient is indifferent, but without anosognosia.. Tests confirm that vision is normal, although the person reports partial or total vision problems.

Simulated blindness

The person invents his own ailment, in this case blindness, to assume the role of a sick person (Münchhausen syndrome).

Bibliographical references:

• Aldrich MS, Alessi AG, Beck RW, Gilman S. Cortical blindness: etiology, diagnosis and prognosis. Ann Neurol 1987; 21: 149 - 158.
• Brogaard, B. (2011). Are there unconscious perceptual processes. Consciousness and Cognition, 20, 449-463.
• O'Reagan, J. & Noë, A. (2001). A sensorimotor account of vision and visual consciousness. Behavioral and Brian Sciences, 24, 939 - 973.