Cortical Blindness and Its Treatment

According to the Texas School for the Blind and Visually Impaired, cortical blindness is a condition used to describe an apparent lack of visual functioning, even with structurally intact eyes. Many believe this is caused by a lack of cortical functioning (from the visual cortex of the brain). Cortical blindness is just one way to describe these conditions. Others include Neurological Visual Impairment (NVI) and Cortical Visual Impairment. These divisions were made to determine what part of the brain was affected.

However, prognosis for this condition is difficult since neither a CAT scan nor a CAT scan nor a VEP can confirm the condition. Treatment for cortical blindness is very likely that one may be treated effectively for this abnormality. Over a long period of time, a series of vision stimulation activities can be completed. The likelihood of a young child recovering from these symptoms is higher than that of an adult. Some believe that the fibers of the optic tract (and their connections in the extrageniculostriate system) may be important in the visual recovery because they maintain the stationary optical image on the retina with reflex eye movements; they are also important for visual feedback of learned skilled movements and can be mediators in visual functioning.

However, many eye conditions exists, but only one other can be compared at great lengths with cortical blindness. In 1917, Riddock noticed in some of his patient’s ability to detect motion without a visual field. This discovery was later described as blind sight. Larry Weiskrantz defined blind sight in 1990 as “the visual discrimination in the absence of acknowledged awareness.” Weiskrantz while studying the disease in the 1970s, found that if you forced someone to guess about whether something is present or not, some participants do better than chance itself.

In his “Blindsight,” he says the disease provides evidence for the idea of the unconscious. He believes that is also explains the idea of a magical or transcendent experience. This dissociation is significant since the two sorts of processing (conscious & unconscious) acquires, processes, and makes use of experience in very different ways.

“Indeed, it seems likely that blindsight (and similar phenomena in other spheres) is an important ingredient of a variety of activities where one wants to move quickly and appropriately, without “thinking about it,” he adds. There have been various other experiments done to determine the cause and effect of this disease. In 1973, Poppel, Held, & Frost carried on an experiment with 4 patients that exhibited visual defects. He asked them to move their eyes to the position of a light flash in their blind field. Many of the people tested asked how they would be able to do the task. This demonstrates the idea that while patients are aware of their disease, they are not willing to attempt to overcome it in many experiences.

These patients are also able to guess with better accuracy whether a specific stimulus presented in a blind area is red or green. This draws the conclusion that whatever distinguishes red sensory states from green sensory states is present even when it is unconscious. Because of these guesses presented within one’s visual field, the guesses of these patients are more likely to be accurate than chance. This striking phenomenon has to do with motion, location and direction. They can shape their hands in a way appropriate to grasping objects as well and also color discrimination is apparently.

Psychologists conclude that these visual stimuli from the blind “spot” are processed in the unconscious state. These patients represent visual features of objects such as color or shape, but these representations are unconscious (as explained before). It was later discovered that these patients may have small regions of intact vision. However they could not come to a conclusion if this light may have shined in their small region of sparred vision. Consciousness in many instances is missing with these patients. The ability to deploy information in reasoning and rational control of action occurs as well. Tony Marcel observed in 1986 a thirsty blindsight patient who would not reach for a glass of water in his blind field. With this, many argue that consciousness must have a direct role in the functioning of somehow enabling information in one’s brain to be used with reasoning and guiding personal action.

In Jason Holt’s book, Blindsight & The Nature of Consciousness, he argued the conscious realism involved with blindsight. He suggested that it helps to reveal certain neural correlates for consciousness because blindsight’s V1 damage also causes conscious visual experience loss. He suggests it is reasonable to believe that V1 plays an active role in conscious experience. He also explains the differences between the blind-field vision and normal vision with these patients. Blindsight patients create trouble for behavioral analysts because it is not clear that these patients lack a certain disposition to discriminate against certain stimuli in their blind field.

In a 1990 study, Corbetta found that eye movement may be slower if the distract or is presented in one of the patient’s blind fields. Ramachandran studied the idea that there are two pathways from the eye to the brain – – one that travels to the cortex (home to the consciousness or older parts) and one to the new parts. Many people also believe that the idea of perception originates in different parts of the brain. According to Marcel in 1993, parallel pathways are the multiple visual pathways in which the brain (with the cortical and subcortical areas) response to motion. When asked to detect stimulus, the patients used blinking, pointing or verbal ways to acknowledge motion. Blinking occurred more often than pointing, and pointing was more prevalent than verbal reporting.

Recently the issue has been brought to light once again. National Geographic News reported in a Nov 1, 2005 article the mystery of blind sight. They described the condition as a phenomenon that occurs in people who suffer injuries to their primary visual cortex in the brain, which is responsible for sight. According to Christopher Mole, a postdoctoral fellow in philosophy at Washington University in St., Louis, this condition allows people to use visual information that they receive through their eyes even though they do not know of this visual experience. He explains that it is hard to prove within a lab.

Although a series of psychologists at Rice University in Houston, think they may have discovered a way to do so by using electromagnetic stimulation on the brains of people who can see to make them partially or temporarily blind. “The way it works is an electric current inducts into the brain via a magnetic pulse, and that causes a disruption of underlying neurons in the brain,” said Tony Ro, a member of the team. “What this technique allows us to do essentially is in a safe and noninvasive way shut down a portion of the brain temporarily.” Their compelling proof of blind sight was reported to the Proceeding of the National Academy of Science Journal along with their other findings.

Some other explanations for blind sight are that eye and pointing responses may be mediated by the superior colliculus and/or through the dorsal visual pathway. Motor responses often occur without conscious awareness; the ventral pathway is required for awareness. Another cause for the disease is bilateral lesions of the primary visual cortex. These patients have a response to light to their pupil. It can also be associated with denial of visual loss (or Anton’s syndrome). All of these explanations conclude the idea that we may not know all that is in our mind and what motivates us to behave in certain ways. Therefore, experiments done with blindsight may be significant evidence for epiphenomenalism. It is shown that certain subliminal details may influence our behavior as can any post-hypnotic ones. The greatest fascination with these studies is the patient’s failure to know what is going on. They may be acting randomly, or even invent their own reasons for the behaviors. This draws the conclusion that we may be in less control of our behavior than previously known.

In conclusion, with various teams of psychologists working on treating the condition, it is only acceptable to believe that results may be found in the near future. Those currently with blind sight such as young children may have hope in being cured of this “in the dark” type of disease.

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