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Biology 202
2001 Second Web Report
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Prosopagnosia: Seeing the World through Fog-Colored Glasses

Caroline Ridgway

With impressive consistency, the visual system, along with each accompanying component that in sum total constitutes a person, develops without error. Patterns of input impinge on complex layers of cells, with the resulting neural interpretation allowing us to negotiate the spatial world around us such that we may avoid causing harm to ourselves or to others. Various devices and techniques have been devised to allow those who are not equipped with a similarly functioning visual system to escape natural selection's discerning grasp. However, various gradations of dysfunction exist between perfect and no vision, which complicate the life of the person suffering from these disorders no less. The disorder prosopagnosia, in particular, otherwise known as "face blindness," causes a crippling deficit in a person's ability to recognize faces (1, 2, 3, 6, 7). It is a somewhat ill understood and deceiving phenomenon. Those individuals suffering from prosopagnosia are able to see perfectly well, to the extent that their perception of visual stimuli is not impaired. However, when presented with a person's face, they are utterly unable to recall having seen that face or having interacted with the person attached to it.

Some people would make the distinction between prosopagnosia and facial agnosia (4, 8), with the former applying only to familiar faces while the latter applies more generally to prevent the recognition of any faces. While this might suggest memory impairment as a possible cause, evidence for perceptual deficits has been consistent (4), thereby refuting the notion that these individuals are simply not able to remember people they have encountered. Specifically, the locus of damage that results in prosopagnosia appears to be the medial occipitotemporal cortex (4), though the disorder may be congenital or acquired (2). Lesions in this somewhat posterior and deeply embedded region of the brain, suggested by some researchers to be bilateral in the instance of this disorder, would be consistent with the presented deficits in perception. However there are certain elements of the research and the disorder which seem counterintuitive. For instance, that these "face blind" individuals only cite difficulty in recognizing familiar faces suggests that the problem may be more than just perceptual. Furthermore, there is separate evidence suggesting that visual processing occurs on a unilateral level (4), and that stimuli are perceived contralaterally. This orientation does not preclude a bilateral lesioning being at the root of prosopagnosia, however it does offer some complicating factors. Given the variety of competing hypotheses, as well as the recognized intricacy of the visual system, it is, as is often the case with neurologically based disorders, likely the case that a complex amalgam of deficits combines to produce the observed effect.

Whatever the neural substrate involved in prosopagnosia, it is clear enough that it involves fairly deep structures and fundamental abilities. Among other things, it suggests the possible existence of a grandmother cell-type arrangement (5) specific to cells designed to recognize faces. If there were such a subset of cells, speaking perceptually, then if the pathway to or from them were to be damaged in some way it would result in only very specific impairment of function. This is a compelling possibility, despite the resounding inefficiency of the grandmother cell hypothesis as a whole, given that prosopagnosia and the corresponding facial agnosia seem to represent different strains of one breed of problem (6). And while prosopagnosia is not thought to be entirely a function of impaired memory, it does equate to a sort of perceptual amnesia, of both the retrograde and anterograde varieties. Providing an additional dimension to the discussion, prosopagnosia is only one representative in a family of neurological disorders. Generalized agnosia (6, 8) may extend to any sensory modality, and may occur in degrees of impairment from case to case. Within face blindness, specifically, patients may vary in their ability to recognize affect or directionality of attention in addition to a more fundamental inability to process faces.

While the exact mechanism of the disorder is still somewhat debated, it is abundantly clear that those afflicted suffer greatly. Though their suffering may not register as physical pain, and prosopagnosia in no ways hinders their ability to make their way through daily obstacles, significant emotional damage can be done stemming from forgotten or missed encounters with people as close as family members. While there are very few recorded cases of prosopagnosia, and it was only named in 1947 (1, 4), the reports of daily trials provided by sufferers are consistent in their degree of frustration and annoyance and despondency. One particularly poignant anecdote describes an incident in which a man who endures the burden of prosopagnosia met his own mother walking down the sidewalk of their neighborhood and did not recognize her (2). He reports that he only became aware of this encounter when she later told him about it. This may represent an extreme example of the hardships caused by face blindness, but similarly awkward and embarrassing events occur frequently. Just as people who are blind in the more conventionally thought of sense learn to rely on the compensatory strength of their other sensory modalities to inform them about their surroundings, an individual who lives with prosopagnosia must adapt to other distinguishing markers, such as a distinctive walk or voice (2, 3, 7). However, these are not always enough to ensure a complete reprieve from what are perceived as being humiliating social blunders, despite their being a function of a neurological impairment. And while a face blind person may develop a fairly consistent accuracy in recognizing people without the benefit of a familiar face, it is difficult to do so without acuity and speed being compromised to some degree.

It is generally difficult for someone who does not find it at all problematic to recognize people by their faces to understand just what prosopagnosia is and how deeply it affects those who do have to deal with it. Beyond the superficial frustration at having to devise alternative methods of recognition, not being able to process information about the face can have damaging consequences for emotional interactions, extending into intimate relationships (2, 7). We rely heavily on the face to gain knowledge about how a person is feeling, and how that person feels about us. This information, in turn, provides us with material we may use to guide our own actions and words. A face blind person not only does not often know who he or she is dealing with, but may not know how to deal with that person, adding an additional layer of difficulty to an already diffuse problem. What is possibly most important in attempting to understand prosopagnosia and all that it entails is that sufferers do not have impaired vision in the sense that they can see objects and people; the difficulty comes in recognizing those objects and people. Furthermore, face blind people do not have any mental deficits or direct impairment to memory. However difficult it may be to understand how a person could not "see" the very thing that guides our everyday interactions, it is important that they be recognized as normal and functioning individuals.

WWW Sources

1) Prosopagnosia (Face Blindness)

2) Face Blind! (By Bill Choisser)

3) Prosopagnosia (Glenn's Page)

4) Prosopagnosia: A look at the laterality and specificity issues using evidence from neuropsychology and neurophysiology

5) Central Visual Pathways: Grandmother Cells

6) Prosopagnosia: Definitional Information

7) Prosopagnosia (Cecilia Burman)

8) NINDS Agnosia Information Page




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