A new study offers the most dramatic demonstration to date of so-called blindsight, the native ability to sense things using the brain’s primitive, subcortical — and entirely subconscious — visual system.
BLINDSIGHT A patient whose visual lobes in the brain were destroyed was able to navigate an obstacle course and recognize fearful faces subconsciously.
Scientists have previously reported cases of blindsight in people with partial damage to their visual lobes. This new report is the first to show it in a person whose visual lobes — one in each hemisphere, under the skull at the back of the head — were completely destroyed. The finding suggests that people with similar injuries may be able to recover some crude visual sense with practice.
“It’s a very rigorously done report and the first demonstration of this in someone with apparent total absence of a striate cortex, the visual processing region,” said Dr. Richard Held, an emeritus professor of cognitive and brain science at the Massachusetts Institute of Technology.
Scientists have long known that the brain digests what comes through the eyes using two sets of circuits. Cells in the retina project not only to the visual cortex, but also to subcortical areas. These include the superior colliculus, which is crucial in eye movements and may have other sensory functions; and, probably, circuits running through the amygdala, which registers emotion.
In an earlier experiment, one of the authors of the new paper, Dr. Alan Pegna of Geneva University Hospitals, found that the same patient had emotional blindsight.
When presented with images of fearful faces, he cringed subconsciously in the same way that almost everyone does, even though he could not consciously see the faces. The subcortical, primitive visual system apparently registers not only solid objects but also strong social signals.
Definition:
If you see two of whatever you are looking at simultaneously, you may have a condition known as double vision, also referred to as diplopia. Double and blurred vision are often thought to be the same, but they are not. In blurred vision, a single image appears unclear. In double vision, two images are seen at the same time, creating understandable confusion for anyone who has it.
People with double vision see two images of one object. the images are separate but often clearly focused. The disorder can be due to a number of causes and it usually disappears when one eye is closed. You should consult your ophthalmologist immediately if you start to experience double vision because it may indicate that you have a serious underlying disorder.
It is commonly known as Diplopia or Double vision. It is the simultaneous perception of two images of a single object. These images may be displaced horizontally, vertically, or diagonally (i.e. both vertically and horizontally) in relation to each other.
Binocular diplopia or double vision
Binocular diplopia is double vision arising as a result of the misalignment of the two eyes relative to each other, such as occurs in Esotropia or Exotropia. In such a case whilst the fovea of one eye is directed at the object of regard, the fovea of the other is directed elsewhere, and the image of the object of regard falls on an extra-foveal area of retina.
The brain calculates the ‘visual direction’ of an object based upon the position of its image relative to the fovea. Images falling on the fovea are seen as being directly ahead, whilst those falling on retina outside the fovea may be seen as above, below, right or left of straight ahead depending upon the area of retina stimulated. Thus, when the eyes are misaligned, the brain will perceive two images of one target object, as the target object simultaneously stimulates different, non-corresponding, retinal areas in either eye, thus producing double vision.
This correlation of particular areas of the retina in one eye with the same areas in the other is known as Retinal correspondence. This relationship also gives rise to an associated phenomenon of binocular diplopia, although one that is rarely noted by those experiencing diplopia: Because the fovea of one eye corresponds to the fovea of the other, images falling on the two foveas are ‘projected’ to the same point in space. Thus, when the eyes are misaligned, the brain will ‘project’ two different images in the same visual direction. This phenomenon is known as ‘Confusion’.
Double vision is dangerous to survival, therefore, the brain naturally guards against its occurrence. In an attempt to avoid double vision, the brain can sometimes ignore the image from one eye; a process known as suppression. The ability to suppress is to be found particularly in childhood when the brain is still developing. Thus, those with childhood strabismus almost never complain of diplopia whilst adults who develop strabismus almost always do. Whilst this ability to suppress might seem a wholly positive adaptation to strabismus, in the developing child this can prevent the proper development of vision in the affected eye resulting in amblyopia. Some adults are also able to suppress their diplopia, but their suppression is rarely as deep or as effective and takes longer to establish. They are not at risk of permanently damaging their vision as a result though. It can appear sometimes, therefore, that diplopia disappears without medical intervention. However, in some cases the cause of the double vision may still be present.
Monocular diplopia
More rarely, diplopia can also occur when viewing with only one eye; this is called monocular diplopia, or, where the patient perceives more than two images, monocular polyopia. In this case, the differential diagnosis of multiple image perception includes a structural defect within the eye, a lesion in the anterior visual cortex (rarely cause diplopia, more commonly polyopia or palinopsia) or non-organic conditions.
Temporary diplopia
Temporary diplopia can also be caused by intoxication from alcohol or head injuries, such as concussion. If temporary double vision does not resolve quickly, one should see an eye doctor immediately. It can also be a side effect of the anti-epileptic drugs Phenytoin and Zonisamide, and the anti-convulsant drug Lamotrigine, as well as the hypnotic drug Zolpidem and the dissociative drug Ketamine.
Voluntary diplopia
Some people are able to consciously uncouple their eyes, inducing double vision on purpose. These people do not consider their double vision dangerous or harmful, and may even consider it enjoyable. It makes viewing stereograms much easier.
Causes:
There are two possible causes. Refractive. Light from an object is split into two images by a defect in the eye’s optical system. Cataracts might, for example, cause such a defect.
Failure of both eyes to point at the object being viewed, a condition referred to as “strabismus” or “squint”. In normal vision, both eyes look at the same object. The images seen by the two eyes are fused into a single picture by the brain. If the eyes do not point at the same object, the image seen by each eye is different and cannot be fused. The result is double vision. Why might eyes not point in the same direction? Possibly because of a defect in the muscles which control the movement of the eyes or in the control of these muscles through the nerves and brain.
The most common cause of double vision is weakness or paralysis of one of more of the muscles that control the movements of one eye. The movement of the affected eye is impaired, causing crossed eyes. Two different views of the same object are received by the visual system and the brain cannot combine them. Tilting or turning the head may briefly correct the problem. however, not all types of crossed eyes cause double vision.
Many serious conditions that affect the brain and nervous system may cause impaired eye movements, leading to double vision. Potential causes include multiple sclerosis, head injuries, brain tumors and bulging of an artery inside the head due to a weakness in the vessel wall. In older people, impaired eye movement resulting in double vision may be linked with diabetes mellitus and rarely with atherosclerosis and high blood pressure.
Double vision can also occur as a result of a tumor or blood clot behind one of the eyes, causing the movement of that eye to be affected.
Implications:
Double vision can be extremely discomforting. The brain acts to alleviate the discomfort by suppressing, or blanking out, one of the images. In young children, if this suppression persists over a continued length of time, it can lead to an impairment of the development of the visual system. The suppressed eye may get to the point where it is unable to see well, no matter how good the spectacle or contact lens correction. Doctors call this condition amblyopia. Since it is a result of a defect in the interpretive mechanisms of the eye and brain, it is more difficult to treat than a refractive condition (one having to do with the eye’s ability to bend light).
Diagnosis:
Your doctor may ask you to shut one eye at a time to see whether the double vision disappears. He or she may also ask you to describe the double images, or ask if they appear side by side or one on top of the other or whether one of the images appears to be tilted. Your doctor will probably observe the movements of your eyes closely in order to establish whether any of the eye muscles are weak or paralyzed. He or she may also carry out special vision tests to identify weak eye movement.
If double vision has come on suddenly, or if no obvious cause can be found, or urgent CT scanning or MRI may be done to check for any abnormality in the eye sockets or brain that might be affecting the alignment of the eyes. You should also have a neurological examination.
Treatment:
Treatment of double vision is aimed at the underlying cause. A serious disorder such as an aneurysm may need hospital treatment. Double vision caused by diabetes mellitus will usually disappear over time. But, if it does not disappear, your doctor may advise wearing a patch cover one eye to eliminate the second image. Muscle surgery is also useful if double vision has been present for some time.
Treatment of double vision consists of eye exercises, surgical straightening of the eye or a combination of the two. Therapy is aimed at re-aligning the squinting eye where possible without surgery and re-stimulating the part of the visual pathway to the brain which is not working correctly.
Efforts must first be made to identify and treat the underlying cause of the problem. Treatment options includes prism lenses and/or vision therapy and/or surgery, and also botulinum toxin can be used. On occasions, in certain conditions such as Oculomotor nerve palsy for example, it may be necessary to occlude one eye either temporarily or permanently. Daily wear of prism lenses is a passive compensatory treatment. Vision therapy is an active treatment which retrains the visual and vestibular systems (brain, eye muscles, and body). Vision therapy may eliminate the need for daily wear of prism lenses but is only suitable for a minority of those with diplopic symptoms.
Disclaimer: This information is not meant to be a substitute for professional medical advise or help. It is always best to consult with a Physician about serious health concerns. This information is in no way intended to diagnose or prescribe remedies.This is purely for educational purpose
Alternative Names : Color deficiency; Blindness – color
Definition: Color blindness is the inability to see certain colors in the usual way.Color blindness, or color vision deficiency, in humans is the inability to perceive differences between some or all colors that other people can distinguish. It is most often of genetic nature, but may also occur because of eye, nerve, or brain damage, or due to exposure to certain chemicals. The English chemist John Dalton in 1798 published the first scientific paper on the subject, “Extraordinary facts relating to the vision of colours”, after the realization of his own color blindness; because of Dalton’s work, the condition is sometimes called Daltonism, although this term is now used for a type of color blindness called deuteranopia.…………....CLICK & SEE
Color blindness is usually classed as disability; however, in selected situations color blind people may have advantages over people with normal color vision. There are some studies which conclude that color blind individuals are better at penetrating certain camouflages. Monochromats may have a minor advantage in dark vision, but only in the first five minutes of dark adaptation.
Causes:
Color blindness occurs when there is a problem with the color-sensing materials (pigments) in certain nerve cells of the eye. These cells are called cones. They are found in the retina, the light-sensitive layer of tissue at the back of the inner eye.
If you are missing just one pigment, you might have trouble telling the difference between red and green. This is the most common type of color blindness. Other times, people have trouble seeing blue-yellow colors. People with blue-yellow color blindness almost always have problems identify reds and greens, too.
The most severe form of color blindness is achromatopsia. A person with this rare condition cannot see any color. Achromatopsia is often associated with lazy eye, nystagmus (small, jerky eye movements), severe light sensitivity, and extremely poor vision.
There are many types of color blindness. The most common are red-green hereditary (genetic) photoreceptor disorders, but it is also possible to acquire color blindness through damage to the retina, optic nerve, or higher brain areas. Higher brain areas implicated in color processing include the parvocellular pathway of the lateral geniculate nucleus of the thalamus, and visual area V4 of the visual cortex. Acquired color blindness is generally unlike the more typical genetic disorders. For example, it is possible to acquire color blindness only in a portion of the visual field but maintain normal color vision elsewhere. Some forms of acquired color blindness are reversible. Transient color blindness also occurs (very rarely) in the aura of some migraine sufferers.
The different kinds of inherited color blindness result from partial or complete loss of function of one or more of the different cone systems. When one cone system is compromised, dichromacy results. The most frequent forms of human color blindness result from problems with either the middle or long wavelength sensitive cone systems, and involve difficulties in discriminating reds, yellows, and greens from one another. They are collectively referred to as “red-green color blindness”, though the term is an over-simplification and is somewhat misleading. Other forms of color blindness are much more rare. They include problems in discriminating blues from yellows, and the rarest forms of all, complete color blindness or monochromacy, where one cannot distinguish any color from grey, as in a black-and-white movie or photograph.
Most color blindness is due to a genetic problem. About 1 in 10 men have some form of color blindness. Very few women are color blind.
The drug hydroxychloroquine (Plaquenil) can also cause color blindness. It is used to treat rheumatoid arthritis, among other conditions.
If your clothes don’t match, someone might have teased you about being color-blind. But some people reallyare color-blind. It doesn’t mean they can’t see any color at all, like a black and white movie. It means that they have trouble seeing the difference between certain colors. (Check out the image on the right to see how well you see colors.)
Being color-blind can make it tricky to match your shirt and pants, but it’s not a serious problem. People who are color-blind can do normal stuff, even drive. Most color-blind people can’t tell the difference between red or green, but they can learn to respond to the way the traffic signal lights up. The red light is generally on top and green is on the bottom.
Cones and Color:
To understand what causes color blindness, you need to know about the cones in your eyes. Cones in your eyes? Yes, but they’re very small. These cones are cells on your retina, an area the size of a postage stamp that’s at the back of your eye.
You have “red,” “blue,” and “green” cones, which are sensitive to those colors and combinations of them. You need all three types to see colors properly. When your cones don’t work properly, or you don’t have the right combination, your brain doesn’t get the right message about which colors you’re seeing. To someone who’s color-blind, a green leaf might look tan or gray.
Color Blindness Is Passed Down:
Color blindness is almost always an inherited (say: in-her-ut-ed) trait, which means you get it from your parents. You get inherited traits through genes(say: jeenz), which determine everything about your body, including how tall you’ll be and whether your hair will be straight or curly.
Eye doctors (and some school nurses) test for color blindness by showing a picture made up of different colored dots, like the one above. If a person can’t see the picture or number within the dots, he or she may be color-blind.
Boys are far more likely to be color-blind. In fact, if you know 12 boys, one of them is probably at least a little color-blind. So girls, the next time a boy asks you if something matches, you’d better lend him a hand!
Symptoms :
Symptoms vary from person to person, but may include:
Trouble seeing colors and the brightness of colors in the usual way
Inability to tell the difference between shades of the same or similar colors
Often, the symptoms may be so mild that some persons do not know they are color blind. A parent may notice signs of color blindness when a child is learning his or her colors.
Rapid, side-to-side eye movements and other symptoms may occur in severe cases.
Exams and Tests:
Your doctor or eye specialist can check your color vision in several ways. Testing for color blindness is commonly done during an eye exam…..….CLICK & SEE
Treatment: THERE IS NO TREATMENT
Outlook (Prognosis) : COLOR BLINDNESS IS A LIFE-LONG CONDITION. MOST PERSONS ARE ABLE TO ADJUST WITHOUT DIFFICULTY OR DISABILITY. .
Possible Complications : THOSE WHO ARE COLORBLIND MAY NOT BE ABLE TO GET CERTAIN JOB THAT NEEDS COLOR VISION. FOR EXAMPLE , A PILOT NEEDS TO BE ABLE TO SEE COLORS.
When to Contact a Medical Professional :
Make an appointment with your health care provider or ophthalmologist if you think you (or your child) have color blindness.
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