Definition:
Prosopagnosia (sometimes known as face blindness) is a disorder of face perception where the ability to recognize faces is impaired, while the ability to recognize other objects may be relatively intact. The term originally referred to a condition following acute brain damage, but recently a congenital form of the disorder has been proposed, which may be inherited by about 2.5% of the population. The specific brain area usually associated with prosopagnosia is the fusiform gyrus.
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It is often accompanied by other types of recognition impairments (place recognition, car recognition, facial expression of emotion, etc.) though sometimes it appears to be restricted to facial identity. Not surprisingly, prosopagnosia can create serious social problems. Prosopagnosics often have difficulty recognizing family members, close friends, and even themselves. They often use alternative routes to recognition, but these routes are not as effective as recognition via the face.
Few successful therapies have so far been developed for affected people, although individuals often learn to use ‘piecemeal’ or ‘feature by feature’ recognition strategies. This may involve secondary clues such as clothing, hair color, body shape, and voice. Because the face seems to function as an important identifying feature in memory, it can also be difficult for people with this condition to keep track of information about people, and socialize normally with others.
Some also use the term prosophenosia, which refers to the inability to recognize faces following extensive damage of both occipital and temporal lobes.
There are a variety of explanations for prosopagnosia. Of course, all these explanations propose that the procedures necessary for normal face recognition are not working properly. However, the explanations differ in their characterization of the impaired procedures. It appears that prosopagnosia actually refers to a number of different types of impairments, so no one explanation will account for all cases of prosopagnosia.
History:-
Selective inabilities to recognize faces were reported throughout the 19th century, and included case studies by Hughlings Jackson and Charcot. However, it was not named until the term prosopagnosia was first used in 1947 by Joachim Bodamer, a German neurologist. He described three cases, including a 24-year old man who suffered a bullet wound to the head and lost his ability to recognise his friends, family, and even his own face. However, he was able to recognize and identify them through other sensory modalities such as auditory, tactile, and even other visual stimuli patterns (such as gait and other physical mannerisms). Bodamer gave his paper the title Die Prosop-Agnosie, derived from classical Greek (prosopon) meaning “face” and (agnosia) meaning “non-knowledge”.
Overview:-
The study of prosopagnosia has been crucial in the development of theories of face perception. Because prosopagnosia is not a unitary disorder (i.e., different people may show different types and levels of impairment) it has been argued that face perception involves a number of stages, each of which can be separately damaged.This is reflected not just in the amount of impairment displayed but also in the qualitative differences in impairment that a person with prosopagnosia may present with.
This sort of evidence has been crucial in supporting the theory that there may be a specific face perception system in the brain. This is counter-intuitive to many people as they do not experience faces as ‘special’ or perceived in a different way from the rest of the world.
A recent case report described a closely related condition called prosopamnesia, in which the subject, from birth, could perceive faces normally but had a severely impaired ability to remember them.
It has also been argued that prosopagnosia may be a general impairment in understanding how individual perceptual components make up the structure or gestalt of an object. Psychologist Martha Farah has been particularly associated with this view.
Until early in the 21st century, prosopagnosia was thought to be quite rare and solely associated with brain injury or neurological illness affecting specific areas of the brain. However, recently a form of congenital prosopagnosia has been proposed, in which people are born with an impairment in recognising and perceiving faces, as well as other objects and visual scenes. The cases that have been reported suggest that this form of the disorder may be heritable and much more common than previously thought (about 2.5% of the population may be affected), although this congenital disorder is commonly accompanied by other forms of visual agnosia, and may not be “pure” prosopagnosia. It has been suggested that very mild cases of face blindness are much more common, perhaps affecting 10% of the population, although there have not been any studies confirming this. The inability to keep track of the identity of characters in movies is a common complaint.
A classic case of a prosopagnosia is presented by “Dr P” in Oliver Sacks‘ 1985 book The Man Who Mistook His Wife for a Hat. Although Dr P could not recognize his wife from her face, he was able to recognize her by her voice. His recognition of pictures of his family and friends appeared to be based on highly specific features, such as his brother’s square jaw and big teeth.
Subtypes
Apperceptive prosopagnosia
Apperceptive prosopagnosia is thought to be a disorder of some of the earliest processes in the face perception system. People with this disorder cannot make any sense of faces and are unable to make same-different judgements when they are presented with pictures of different faces. They may also be unable to work out attributes such as age or gender from a face. However, they may be able to recognise people based on non-face clues such as their clothing, hairstyle or voice.
Associative prosopagnosia
Associative prosopagnosia is thought to be an impairment to the links between early face perception processes and the semantic information we hold about people in our memories. People with this form of the disorder may be able to say whether photos of people’s faces are the same or different and derive the age and gender from a face (suggesting they can make sense of some face information) but may not be able to subsequently identify the person or provide any information about them such as their name, occupation or when they were last encountered. They may be able to recognise and produce such information based on non-face information such as voice, hair, or even particularly distinctive facial features (such as a distinctive moustache) that does not require the structure of the face to be understood. Typically such people do not report that ‘faces make no sense’ but simply that they do not look distinctive in any way.
Developmental prosopagnosia
Developmental prosopagnosia (DP) is a face recognition deficit that is lifelong, manifests itself in early childhood and that cannot be attributed to acquired brain damage. However, a number of studies have found functional deficits in DP both on the basis of EEG measures and fMRI. It has been suggested that a genetic factor is responsible for the condition.
There seem to be two categories of DP patients:
– patients who are impaired in basic face processing (age estimation, judgment of facial affect) and also show deficits on other forms of visual processing;
– patients with pure face recognition impairments in the presence of intact basic visual processing.
The first group of patients fail to obtain view-centered descriptions. According to the Bruce and Young model of face recognition, these are precursors of the more abstract expression-independent descriptions. View-centered descriptions do not seem to be specific for faces, as the patients with impairments of processing the physical aspects of faces also show difficulties in non-facial tasks like object recognition or tests of visuo-spatial abilities.
However, there is as yet only limited evidence for a classification into different subtypes.
There are many developmental disorders that incorporate within themselves an increased likelihood that the person will have differences in face perception, of which the person may or may not be aware. That is to say, the person may or may not have insight in the clinical sense of the word. However, the mechanism by which these effects take place is largely unknown. A partial list of some disorders that often have prosopagnosiac components would include nonverbal learning disorder, Williams syndrome, and autism spectrum disorders in general. However, these types of disorders are very complicated, so arbitrary assumptions should be avoided.
Unconscious face recognition:-
One particularly interesting feature of prosopagnosia is that it suggests both a conscious and unconscious aspect to face recognition. Experiments have shown that when presented with a mixture of familiar and unfamiliar faces, people with prosopagnosia may be unable to successfully identify the people in the pictures, or even make a simple familiarity judgement (“this person seems familiar / unfamiliar”). However, when a measure of emotional response is taken (typically a measure of skin conductance), there tends to be an emotional response to familiar people even though no conscious recognition takes place.[9]
This suggests emotion plays a significant role in face recognition, perhaps unsurprising when basic survival (particularly security) relies on identifying the people around you.
It is thought that Capgras delusion may be the reverse of prosopagnosia. In this condition people report conscious recognition of people from faces, but show no emotional response, perhaps leading to the delusional belief that their relative or spouse has been replaced by an impostor.
Symptoms :-
Everyone sometimes has trouble recognizing faces, and it is even more common for people to have trouble remembering other people’s names. Prosopagnosia is much more severe than these everyday problems that everyone experiences. Prosopagnosics often have difficulty recognizing people that they have encountered many times. In extreme cases, prosopagnosics have trouble recognizing even those people that they spend the most time with such as their spouses and their children.
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One of the telltale signs of prosopagnosia is great reliance on non-facial information such as hair, gait, clothing, voice, and other information. Prosopagnosics also sometimes have difficulty imagining the facial appearance of acquaintances. One of the most common complaints of prosopagnosics is that they have trouble following the plot of television shows and movies, because they cannot keep track of the identity of the characters.
If you would like to assess your face recognition abilities, we currently have two tests of face recognition available. These tests include feedback on how your scores compare to the scores of people with normal face recognition.
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Diagnosis (Test):
Screening for prosopagnosia is not an easy task, as what most doctors would say. Because of this, a specific tool in the diagnosis for prosopagnosia was developed, called Cambridge Face Memory Test. This is a test that is much reliable and can effectively test for a person’s ability to recognize faces. There was previous a test called Benton which also aims in testing the person for face recognition problems.
The difference between the two tests is that the Cambridge Face Memory test uses faces alone; without hair, ears or neck. While Benton uses images of faces with hair, ears and neck making the test provide results as false-negative. But the Cambridge Face Memory test is not considered the gold standard of prosopagnosia since the brain is a very complex part of a person’s body, which can alter its way of functioning. According to reports, the test is not widely used for it’s still in the process of making it a good and viable test for prosopagnosia.
Other tests such as the EEG and fMRI can be of health in the diagnosis of the condition, most especially the developmental prosopagnosia.
Risk factors:
Those at risk of this condition are the people who have a family history of prosopagnosia. Those with first degree family members who suffer from prosopagnosia are most likely to develop such condition. It has been reported that children of a person with prosopagnosia are at risk of the condition. Other risk factors include the following:
*People who suffered from brain injury.
*People who have had stroke.
Those who have neurodegenerative disorders are also at risk of developing prosopagnosia.
Causes :-
Most of the cases of prosopagnosia that have been documented have been due to brain damage suffered after maturity from head trauma, stroke, and degenerative diseases. These are examples of acquired prosopagnosia: these individuals had normal face recognition abilities that were then impaired. It seems likely that more cases of acquired prosopagnosia have been published for two reasons. First, their impairment with faces is usually quite apparent to these individuals, because they have experienced normal face recognition in the past and so they quickly notice their impairment. Second, because these individual have had brain damage, they are in contact with medical doctors who have assessed their face recognition abilities. (Note that if you have experienced a noticeable decline in your face recognition abilities, you should contact a neurologist immediately. Any sudden decline may indicate the existence of a condition that needs immediate attention.)
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In contrast, in cases of developmental prosopagnosia, the onset of prosopagnosia occurred prior to developing normal face recognition abilities (adult levels of face recognition are reached during teenage years). Developmental prosopagnosia has been used to refer to individuals whose prosopagnosia is genetic in nature, individuals who experienced brain damage prior to experience with faces (prenatal brain damage or immediate brain damage), and individuals who experienced brain damage or severe visual problems during childhood. However, these etiologies should be differentiated, because they are different paths to prosopagnosia and so probably result in different types of impairment; they could be referred to as genetic prosopagnosia, preexperiential prosopagnosia, and postexperiential prosopagnosia, respectively. In some cases, it may be difficult to determine the cause of prosopagnosia, but many times individuals will either know that family members are also prosopagnosic or be aware of potential incidents that may have resulted in brain damage.
Individuals with developmental prosopagnosia often do not realize that they are unable to recognize faces as well as others. Of course, they have never recognized faces normally so their impairment is not apparent to them. It is also difficult for them to notice, because individuals with normal face recognition rarely discuss their reliance on faces. As a result, there are a number of individuals who have not recognized their prosopagnosia until well into adulthood. We have been contacted by far more developmental prosopagnosics than acquired prosopagnosics, and so it may be that this condition is more common than acquired prosopagnosia.
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Treatment:-
Prosopagnosia might be an enduring condition. However, patients may eventually recover if the damage is confined to their right hemisphere (Goldsmith and Liu, 2001). A study that tracked 18 people with prosopagnosia found that the time required for 50% of the people to recover was 9 weeks. Bilateral damage may be necessary in order for the people with prosopagnosia symptoms to endure past and acute period (Goldsmith and Liu, 2001).
However, for people whose prosopagnosia does not go away on it’s own, there is no real treatment. However, there are lifestyle changes that can help people to cope. Often learning to identify clothing, or distinctive features of people may help in recognition. Another helpful thing is to right down list of who you expect to see. Therefore, when you see someone you already have ideas about who they could be.
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Cecilia Burman wrote about what it is like to have prosopagnosia. She knows from experience. Please visit her website and read as much as you can. The following link goes to a page where she talks about how she has adapted and learned to identify people as best and as fast as she can. She also points out that all people with prosopagnosia are not alike. They are as different as can be. Their only similarity is their face-blindness.
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You may click to see :-
*Prosopagnosia Research
* Research Centres and study of Prosopagnosia
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.
Resources:
http://www.faceblind.org/research/index.html
http://en.wikipedia.org/wiki/Prosopagnosia
http://www.macalester.edu/psychology/whathap/UBNRP/visionwebsite04/p%20treatment.html
Prosopagnosia
