According to A.J. Larner's book, "A Dictionary of Neurological signs," prosopagnosia is a neurological condition, "a form of visual agnosia characterized by an inability to recognize previously known human faces or equivalent stimuli (hence a retrograde defect) and to learn new ones (anterograde defect)" (Larner, 2010). Larner further distinguishes between two forms of prosopagnosia: apperceptive and associative agnosia. This "category-specific recognition disorder," as G, Neil Martin calls it in his "Human Neuropsychology" is often, but not always, associated with other forms of visual agnosia such as alexia or achromatopsia.
Prosopagnosia can be congenital or developmental, or a consequence of brain damage, following a stroke, a brain injury, or caused by a degenerative disease (Kinai, 2013) . There are two types of prosopagnosia: apperceptive prosopagnosia and associative prosopagnosia. This form of visual impairment has various degrees of manifestation, from mild to severe and can or cannot be associated with other types of cognitive impairments. The term prosopagnosia has been coined in 1947 in the Bodamer report, but the condition is reported as having been recorded for the first time "as the inability to recognize familiar faces" in the nineteenth century, when Quaglino and Borelli described it "as a specific syndrome" in 1867(Capruso et alii, ).
Ever since the brain of a prosopagnosic patient first came under the scrutiny of scientists, researchers have attempted to explain what exactly is happening in the brain of the respective patient, where and which parts of the brain may be affected as well as find out clues leading to explanations of how the brain functions are affected in those areas. The fact that there are numerous types of prosopagnosia as well as the potential presence or absence of other forms of agnosia makes the research in the field extremely difficult.
The first and most obvious way to find out if someone may have prosopagnosia is through a series of tests. However, the diagnosis of prosopagnosia is more difficult than it may appear at a first glance. In the paper "Diagnosing Prosopagnosia: Effects of ageing, sex, and participant -- stimulus ethnic match on the Cambridge Face Memory Test and Cambridge Face Perception Test," researchers from several academic institutions from around the world have gathered their research results related to the reliability of clinical tests such as Cambridge Face Memory Test (CFMT) and Cambridge Face Perception Test (CFPT). In their assessment of the accuracy of the two mentioned clinical tests, the authors point out that the tests have been developed with the participation of young up to middle aged participants. They stress the necessity to continue the research in the field of testing with older participants, using sample faces that vary in age, for example.
The ethnic match factor is another important element that the authors pinpoint as potentially decisive or inconclusive in establishing a diagnosis: "In the "other-race effect," memory and perceptual discrimination is poorer for faces not of the participant's race than for own race faces" (Bowles, McKone, Dawel, Duchaine, Palermo, Schmalzl, Rivolta, Wilson, Yovel, 2009). In this respect, the authors conclude that "country-specific norms" could help reduce the possibility of getting false results of prosopagnosia diagnosis. The authors further stress the importance of noticing the age-related decline in participants, concluding as consequence of their own testing that "age-related decline begins at approximately 50 years of age" (Bowles, McKone, Dawel, Duchaine, Palermo, Schmalzl, Rivolta, Wilson, Yovel, 2009). Thus, for testing, additional to "country specific norms," there are "age-specific norms" that need to be taken into consideration, especially for participants over the age of 50(idem).
Sex differences were also found to make a potentially significant difference in older participants. Furthermore, the duration of memorization can make an additional difference in a prosopagnosia diagnosis, as the authors of the paper in question shortly underline. Accordingly, poor performance in the results of the Cambridge test based on famous faces vs. higher performance in the other two Cambridge tests based on novel faces may lead, according to the authors, to more accurate results in the establishment of a prosopagnosia diagnosis. The results of the studies in the aforementioned paper are destined to establish a prevalence of the developmental prosopagnosia in the population of a certain country. After having performed their own testing, using CFPT, CFMT, the authors conclude that the norms for further research and developing of testing need to take into consideration factors such as, age, sex, ethnicity, intelligence in the general population and further study and research to increase their reliability.
Looking at the literature on the topic prosopagnosia, a neurological condition, it is easily understandable why the results of the research have advanced only slowly and have taken a huge step forward only lately. As shown before, the diagnosis itself is the first step that needs further research. In the early 1990s, the studies dedicated to prosopagnosia, although much advanced compared to those from the mid twentieth century, were still pretty confusing. In his Brain Circuits and Functions of the Mind: Essays in Honor of Roger Wolcott Sperry, Author, edited by Colwyn B. Trevarthern, Roger Wolcott Sperry considered the scarcity of information regarding the nature of the human ability to distinguish faces. Scientists were debating on the topic of prosopagnosia being inborn or acquired. The very "human" nature of this ability makes the research even more difficult since studies on animals are limited to the perception of objects, faces among them, but not specific, and their reaction responses in specific parts of the brain. In this sense, Sperry makes an interesting observation: the distinction between apperceptive and associative prosopagnosia has been made more than a century ago, when Lissauer concluded that there are patients who "are unable to match or copy a picture presented to them" (apperceptive prosopagnosia), along with others that "fail to recognize objects or pictures in spite of adequate visual capacity" and their "ability to copy accurately an object or picture even if unable to appreciate its name or nature" (Sperry, ed. Trevarthern,1990).
At the beginning of the twenty-first century, in the field of cognitive neuroscience, the research dedicated to prosopagnosia focuses on the brain regions where the process of recognizing faces takes place. Following fMRI studies on humans, researchers have observed that "within ventral temporal cortex" there is "a discrete region in the middle fusiform gyrus, the fusiform face area (FFA), that responds preferentially to faces as compared to assorted common objects"(Marotta, Genovese, Behrmann, 2001).
In 2008, in their book, Walsh and Hoyt's Clinical Neuro-ophthalmology: The Essentials, editors Nancy J. Newman, Neil R. Miller, Valerie Biousse, chapter 13, "Central Disorders of the Visual Function," putting together information resulted from research on the condition of prosopagnosia were making a very interesting remark related to the damaged parts of the human brain that appear to be linked with the condition: "all autopsied cases of prosopagnosia have bilateral lesions, often symmetric, presumably affecting homologous regions of both hemispheres" (ed. Newman, Miller, Biousse, 2008). The ophthalmologist's input in the research in the field of prosopagnosia proves thus to be of essence: "a left-sided hemisphere lesion or a lesion of the splenium of the corpus callosum might disconnect a right hemispheric locus for facial recognition from visual input of the right hemifield, with critical effects in cases of left homonymous hemianopia"(idem). The researchers further confirm that prosopagnosia can manifest along with other visual impairments or independently. After having covered the subject of acquired prosopagnosia, the authors appear to be disregarding the importance of developing the topic of developmental prosopagnosia and mention it briefly in their section dedicated to prosopagnosia.
G. Neil Martin was drawing another interesting conclusion in the chapter dedicated to prosopagnosia, in his book Human Neuropsychology: "to date, prosopagnosia has never occurred in pure form, i.e. without associated perceptual deficits" (Martin, 2006). He describes specific cases that manifested a form of prosopagnosia that illustrate the various degrees of the gravity of the condition. They are illustrative to the better understanding of the multitude of variations in the degree of severity as well as the variations in manifestation along with other disorders. Martin introduces prosopagnosia as "the best-known and most well documented category-specific disorder," further detailing with specific cases that have been reported ever since scientists have discovered it.
Although well-documented and studied, the condition still presents many challenges to neuroscientists. Martin raises questions that have been asked and research done in trying to find answers, but he does not appear to be able to bring the relevant conclusions to them: "is it a form of object visual agnosia or is it a form that is specific to faces? Or perhaps is it an inability to identify individuality in a class of objects"(Martin, 2006). Martin further shows how much more complicated the topic may be, by introducing the hypothesis that it may also be a case of "impairment of memory" (Martin, 2006). "Impaired familiar face perception often indicates amnesia, for example, and prosopagnosics are poor at learning new faces (as are amnesiacs)"(idem)
Interestingly enough, Nancy Mindick, author of Understanding Facial Recognition Difficulties in Children: Prosopagnosia Management…