Prosopagnosia
Prosopagnosia, also known as face blindness, is a cognitive disorder of face perception in which the ability to recognize familiar faces, including one's own face, is impaired, while other aspects of visual processing and intellectual functioning remain intact. The term originally referred to a condition following acute brain damage, but a congenital or developmental form of the disorder also exists, with a prevalence of 2–2.5%.
A common misconception is that prosopagnosics see faces' contours and details as blurry or distorted. The condition is not characterized by warped visuals. Seeing distorted faces is a common symptom of prosopometamorphopsia, not prosopagnosia.
Etymology
Prosopagnosia is a medical Latin term adopted in 1948 into English from the German Prosopagnosie. It is derived from the Greek prosopon,, and agnosia,. The latter is formed from a-,, and gnōstos,.Physiology
The brain area usually associated with prosopagnosia is the fusiform gyrus, which activates specifically in response to faces. The functionality of the fusiform gyrus allows most people to recognize faces in more detail than they do similarly complex inanimate objects. For those with prosopagnosia, the method for recognizing faces depends on the less sensitive object-recognition system. The right hemisphere fusiform gyrus is more often involved in familiar face recognition than the left. It remains unclear whether the fusiform gyrus is specific for the recognition of human faces or if it is also involved in highly trained visual stimuli. Under normal conditions, prosopagnosic patients are able to recognize facial expressions and emotions.Acquired prosopagnosia results from occipital-temporal lobe damage and is most often found in adults. It is subdivided into apperceptive and associative prosopagnosia.
Degenerative prosopagnosia is a form of acquired prosopagnosia that stems from a degenerative disease such as Parkinson's, Alzheimer's, or posterior cortical atrophy.
In congenital prosopagnosia, a person never adequately develops the ability to recognize faces, and areas such as the right fusiform gyrus are underdeveloped, likely due to a genetic predisposition. Prosopagnosia as a whole tends to last throughout one's life. This is especially true of congenital prosopagnosia.
Treatment
There are no widely accepted treatments. Though there have been several attempts at remediation, no therapies have demonstrated lasting improvements across a group of prosopagnosics. Prosopagnosics often learn to use "piecemeal" or "feature-by-feature" recognition strategies. This may involve secondary clues such as clothing, gait, hair color, skin color, body shape, and voice.Implications
Because the face seems to function as an important identifying feature in memory, it can be difficult for prosopagnosics to keep track of information about people and socialize normally.Prosopagnosia has also been associated with other disorders associated with nearby brain areas: left hemianopsia, achromatopsia, and topographical disorientation.
Types
Apperceptive
Apperceptive prosopagnosia has typically been used to describe cases of acquired prosopagnosia with some of the earliest processes in the face perception system. The brain areas thought to play a critical role in apperceptive prosopagnosia are right occipital temporal regions. People with this disorder cannot make any sense of faces and are unable to make same–different judgments when presented with pictures of different faces. They cannot recognize familiar or unfamiliar faces. In addition, apperceptive sub-types of prosopagnosia struggle to recognize facial emotion. But some can recognize people by non-face clues, such as clothing, hairstyle, skin color, or voice. Apperceptive prosopagnosia is believed to be associated with impaired fusiform gyrus. Experiments on the formation of new face detectors in adults on face-like stimuli indicate that such new detectors are formed not in the fusiform but in the lingual gyrus.Associative
Associative prosopagnosia has typically been used to describe cases of acquired prosopagnosia with spared perceptual processes but impaired links between early face perception processes and the semantic information humans hold about people in our memories. Right anterior temporal regions may also play a critical role in associative prosopagnosia. People with this form of the disorder may be able to tell whether photos of people's faces are the same or different and derive the age and sex from a face 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. Associative prosopagnosia is thought to be due to impaired functioning of the parahippocampal gyrus.Developmental
Developmental prosopagnosia, also called congenital prosopagnosia, is a face-recognition deficit that is lifelong, manifesting in early childhood, and that cannot be attributed to acquired brain damage. While developmental prosopagnosia begins early in life, many people do not realize that they have DP until later in their adult lives. 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. The term hereditary prosopagnosia was introduced if DP affected more than one family member, essentially accenting the possible genetic contribution of this condition. To examine this possible genetic factor, 689 randomly selected students were administered a survey in which seventeen developmental prosopagnosics were quantifiably identified. Family members of fourteen of the DP individuals were interviewed to determine prosopagnosia-like characteristics, and in all fourteen families, at least one other affected family member was found. Individuals with congenital prosopagnosia have no mental images of faces, including of close relatives, but they may be able to recognize emotions. Under optimal conditions, recognition of facial expressions and emotions is normally preserved, though under more challenging conditions, it may exhibit subtle deficits.In 2005, a study led by Ingo Kennerknecht showed support for the proposed congenital disorder form of prosopagnosia. This study provides epidemiological evidence that congenital prosopagnosia is a frequently occurring cognitive disorder that often runs in families. The analysis of pedigree trees formed within the study also indicates that the segregation pattern of hereditary prosopagnosia is fully compatible with autosomal dominant inheritance. This mode of inheritance explains why HPA is so common among certain families.
Cause
Prosopagnosia can be caused by lesions in various parts of the inferior occipital areas, fusiform gyrus, and the anterior temporal cortex. Positron emission tomography and fMRI scans have shown that, in individuals without prosopagnosia, these areas are activated specifically in response to face stimuli. The inferior occipital areas are mainly involved in the early stages of face perception and the anterior temporal structures integrate specific information about the face, voice, and name of a familiar person.Acquired prosopagnosia can develop as the result of several neurologically damaging causes. Vascular causes of prosopagnosia include posterior cerebral artery infarcts and hemorrhages in the infero-medial part of the temporo-occipital area. These can be either bilateral or unilateral, but if they are unilateral, they are almost always in the right hemisphere. Recent studies have confirmed that right hemisphere damage to the specific temporo-occipital areas mentioned above is sufficient to induce prosopagnosia. MRI scans of patients with prosopagnosia showed lesions isolated to the right hemisphere, while fMRI scans showed that the left hemisphere was functioning normally. Unilateral left temporo-occipital lesions result in object agnosia, but spare face recognition processes, although a few cases have been documented where left unilateral damage resulted in prosopagnosia. It has been suggested that these face recognition impairments caused by left hemisphere damage are due to a semantic defect blocking retrieval processes that are involved in obtaining person-specific semantic information from the visual modality.
Other less common etiologies include carbon monoxide poisoning, temporal lobectomy, encephalitis, neoplasm, right temporal lobe atrophy, injury, Parkinson's disease, and Alzheimer's disease.
Diagnosis
Few neuropsychological assessments can definitively diagnose prosopagnosia. One commonly used test is the famous faces tests, where people are asked to recognize the faces of famous people. This test is difficult to standardize. Neuropsychologists also use the Benton Facial Recognition Test to assess face recognition skills. Subjects are presented with a target face above six test faces and asked to identify which test face matches it. The images are cropped to eliminate hair and clothes, as many people with prosopagnosia use hair and clothing cues to recognize faces. For the first six items only one test face matches the target face; during the next seven, three of the test faces match but the poses are different. The BFRT's reliability was questioned when a study by Duchaine and Nakayama found that the average score for 11 self-reported prosopagnosics was within the normal range. One reason for this may be the way the test is designed. People with developmental prosopagnosia often use piecemeal strategies, which this test encourages by providing the target face to compare with possible matching faces. As the test increases in difficulty more and more facial features become obscured due to position and lighting, leading normal control subjects to rely on the exact same strategy of looking for individual features to match with the target face.The test may be useful for identifying patients with apperceptive prosopagnosia, since this is mainly a matching test and they are unable to recognize both familiar and unfamiliar faces. They would be unable to pass the test. It would not be useful in diagnosing patients with associative prosopagnosia since they are able to match faces.
The Cambridge Face Memory Test was developed by Duchaine and Nakayama to better diagnose people with prosopagnosia. This test initially presents individuals with three images each of six different target faces. They are then presented with many three-image series, which contain one image of a target face and two distractors. Duchaine and Nakayama showed that the CFMT is more accurate and efficient than previous tests in diagnosing patients with prosopagnosia. Their study compared the two tests and 75% of patients were diagnosed by the CFMT, while only 25% of patients were diagnosed by the BFRT. But as in the BFRT, patients are essentially being asked to match unfamiliar faces, as they are seen only briefly at the start of the test. the test was not widely used and needed further testing before it could be considered reliable.
The 20-item Prosopagnosia Index is a freely available and validated self-report questionnaire that can be used alongside computer-based face recognition tests to help identify prosopagnosics. It has been validated using objective measures of face perception ability, including famous face recognition tests and the CFMT. Less than 1.5% of the general population score above 65 on the PI20 and less than 65% on the CFMT.