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What life is like with prospagnosia? Damage to the brain can result in many different types of abnormal behavior depending on the extent and area of injury. One area of significance, visual agnosia, was a term coined by Sigmund Freud to describe the inability to merge singular visual impressions into a comprehensive pattern (Kolb & Whishaw, 1996). This effect was seen to occur despite the individual having undiminished fundamental perceptual competency in areas like acuity and brightness discrimination.
A particular form of visual agnosia is that of prospagnosia, a relatively rare, but extremely disabling condition in that its sufferers are unable to recognize and identify familiar faces, including their own. The term prospagnosia is derived from the Greek words prison for face, and agnosia meaning not knowing, and is to be distinguished from facial agnosia which applies to recognition of any face, whether it is familiar or not. Individuals with the disorder are able to discern a face; for example, they can detect whether a face is organized into a face pattern, or jumbled into a non-face pattern (Blanc-Gain, 1984, cited in De Haan, Young & Newcombe, 1992). They can also discriminate between isolated features such as the mouth and nose, and often become adept at recognizing familiar people using other cues, such as the voice and gait. The familiar face, however, need not be human. Assal, Favre and Anderes (1984, cited in Ellis & Young, 1996), for example, have reported on a case where the patient became unable to recognize familiar animal faces.
While the first earliest cases were reported in the Deutsche Z. Nervenheilkd in 1892, the disorder was not named until 1947, when a German psychologist, Bodamer, reported on a young man who, as a result of a bullet wound to his head had become unable to recognize friends, family or his own mirror image, although he could distinguish between them by using his other sensory modalities; he could also recognize them through other visual stimuli, such as mannerisms and gait (Takamura, 1996). Although there may be a genetic component in the condition, it is probably more commonly acquired through injury or disease. Strictly speaking, there are many different types of prospagnosia, and therefore it cannot be classed as a unitary disorder. However, as Ellis and Young (1996) have pointed out, classification of the diverse range of this disorder has been hampered by the rarity of its occurrence as an isolated deficit. Moreover, while modern scanning techniques have pinpointed the area of damage for this condition to impairment in the medial occipitotemporal cortex, there remain many controversial issues to be resolved.
The main issues include: 1) debate over whether prospagnosia develops as a result of unilateral or bilateral damage to the cerebral hemispheres; 2) whether failure of parts of episodic memory or the perceptual mechanisms are the main effects of prospagnosia; and 3) whether there is a specific area of the brain designated to face processing (Takamura, 1996). This essay will specifically review these issues, and attempt to reach some consensus on each point. The debate over which hemisphere is damaged in this disorder was begun in 1962, when a study by Hecaen and Angerlergues (1962, cited in McCarthy & Warrington, 1990) suggested that patients with prospagnosia often have impairment in their left visual field. They had found that out of twenty-two patients with prospagnosia, sixteen had damage in the right hemisphere (which would correlate with left visual field impairment), four had bilateral damage and only two had damage in the left hemisphere.
This finding was also later supported in a study by De Renzi, Faglioni and Spinnler (1968) with two different experiments. In their first experiment they investigated whether face fragments presented alone would be identified when matched with the whole face picture. The results of this experiment were similar to Hecaen et al. s findings in that, out of 114 unilaterally damaged patients, those who performed worst on the tasks were those with right brain damage. However, they also found that those patients with right hemisphere damage, but no left visual field deficit, performed better than those with corresponding left visual field damage.
This finding led De Renzi et al. to conclude that impairment of face recognition in right hemisphere damaged patients was a result of the failure to process discriminating variances and the integration of visual cues, and therefore, most probably a perceptual deficit. However, in order to determine whether memory impairment or a perceptual deficit were the principal problem in this disorder, De Renzi et al. s (1968) second experiment involved a delayed memory task. The rationale behind this experiment was that if memory were vital for face recognition then patients with this disorder would show the greatest impairment in this task. As this effect did not occur, leading De Renzi et al.
concluded that memory impairment was not the main difficulty in prospagnosia, thus lending further support to their earlier findings of a perceptual deficit. Damasio, Damasio and Van House (1982, cited in Takamura, 1996), however, disputed the proposal of purely right hemisphere damage when they reviewed the post-mortem reports of the patients from the original Hecaen et al. (1962, cited in McCarthy & Warrington, 1990) studies and found that all the patients revealed bilateral lesions. It was suggested that the lesions in the medial occipitotemporal regions were silent because they had not shown up on the original clinical neurological examinations: at that point, such techniques were not reliable enough to detect the laterality of damage in prospagnosia. Damasio et al. thus proposed that the silent lesions were the principal cause of the disorder where the patient seems to have unilateral damage. The current widely accepted theory of face processing, however, is perhaps, that provided by Bruce and Young (1986).
In their information-processing model Bruce and Young consider that face processing occurs alongside expression analysis, facial speech analysis and directed visual processing. They suggest that there is a group of face recognition units that provide a connection between the structural encoding of the faces appearance and the person identity nodes. These nodes supply stored information of known people (e. g. their occupation and characteristics). The face recognition unit holds the fundamental description of a known persons appearance and fires when a seen face correlates with a stored description.
There are, therefore, particular functional stages, starting with the structural encoding of the faces semblance, leading to the firing of the face recognition units able to respond to individual parts or configurations of a familiar face. The person will then retrieve the necessary stored semantic information and finally, produce the appropriate name. Other cues for familial recognition of a person, such as the voice or gait will reach the person identity nodes via separate access routes. In support of Bruce and Youngs (1986) model, Sergent (1992, cited in Takamura, 1996) has used positron emission tomography (PET) and magnetic resonance imaging (MRI) to demonstrate that there are specific brain areas that execute facial recognition processing. By comparing the PET scans of prosopagnosics with the normal patients, Sergent detected three main areas in the occipitotemporal lobe that lit up in the normal processing of a familiar face, but did not light up in the prosopagnosics. These areas, Sergent suggests, could be anatomically correlated to Bruce and Youngs model: the area in the posterior occipital region may be concerned with the perceptual action of eliciting the unique facial features.
Another area, which is slightly anterior to the first, could be involved with forming the connections between the face and the biographical information and relate to Bruce and Youngs structural encoding stage. A further area, just in front of the previous area, in the temporal lobe, may act like a filing cabinet, storing the biographical data and correlate with the biographical memory stage. Evidence of these aggregates of face cells in distinct brain regions along the occipitotemporal pathway suggest that there may be a specific face pathway, as part of the main visual processing pathway. However, as Perrett, Mistlin and Chitty (1988, cited in Takamura, 1996) point out, the evidence should be treated with caution, since it does not demonstrate that there is an exclusive brain area for face processing, merely that a facial processing subsystem exists within specific brain regions. Relating Bruce and Youngs model to the debate over whether prospagnosia is due to a deficit in memory or perception, Damasio (1985, cited in Takamura, 1996) purports that the disorder is exclusively linked with the third stage of Bruce and Youngs model, that of the biographical memory retrieval parts. But other evidence suggests that this may not be so.
In a double dissociation situation Assal, Faure and Andre (1984, cited in Ellis & Young, 1995), for example, have related the case of a farmer who was able to recognize each of his cows (zooagnosie), but not his friends and family. Conversely, Buyer (1991, cited in Bauer, 1993) have written of a farmer with a reversal of this condition. But Takamura (1996) has suggested that, rather than assuming that there is a cow pathway, it would probably be more correct to infer that, for persons in close daily contact with such animals, there is a specific biographical representation built up in the association cortices. Other cases of prospagnosia which occur with visual object agnosia (e. g. Faust, 1955, cited in McCarthy & Warrington, 1990) also dispute Damasio's (1985) claim that there is no perceptual element involved.
Furthermore, studies by Perrett, Mistlin and Chitty (1987, cited in Takamura, 1996) have demonstrated that the cells in the superior temporal sulcus are sensitive to changes of orientation and profiles of faces. This would suggest that these cells are probably involved in visual analysis, rather than any other higher processing. The facial pathway model can involve different types of facial recognition. It would therefore seem incorrect to accept the bilateral ists view of prospagnosia as a biographical information retrieval problem, because it appears to be restrictive describing as it does only the last stage of Bruce and Youngs model. From this viewpoint, it would seem then that the issue of laterality is one that requires further debate. The main problem appears to be in deciding whether bilateral lesions are necessary for complete prospagnosia, or whether unilateral lesions are responsible for certain parts of prospagnosia.
But Takamura (1996) has questioned whether such discussion is necessary. In view of the fact that the brain is asymmetric, it may be that the hemispheres work by different mechanisms, with the same final result. Therefore, it may be possible that both hemispheres have a role to play in facial processing, although because of the mechanisms they use, one of the hemispheres may be more competent at processing than the other. Perrett, Smith, Potter, Mistlin, Head, Milner and Jeeves (1984, cited in Bruce, 1988), for example, in their proposal that there is an asymmetric distribution of face cells may have accounted for why Damasio (1985, cited in Takamura, 1996) discovered larger left hemisphere lesions, while the right hemisphere probably holds the main area for face processing since it has the largest proportion of specific face cells.
Moreover, Tovee and Tovee (1993, cited in Takamura, 1996) have shown that the right hemisphere is best at fundamental configurational processing, and therefore would be better equipped at efficient visual processing. However, as Sergent (1994, cited in Takamura, 1996) has stated, probably the best conclusion we can reach at the moment on this issue, is that facial processing is probably a bilateral, but asymmetric process, encompassing both the cerebral hemispheres. In conclusion, it is clear that despite advances in scanning techniques there is still a great deal of disagreement over some fundamental issues regarding prospagnosia. In attempting to answer the questions posed at the beginning of the essay we have reached a consensus on some points, but in other areas have to hazard a guess at the most likely conclusions. Looking at the issue of laterality, however, it would seem likely that although the right hemisphere is probably the most proficient at face processing (although it could just be pattern processing), but for full prospagnosia to develop bilateral lesions are necessary. Likewise, prospagnosia is most likely to be characterized by both memory and perceptual deficits depending on the stage at which the lesion has developed.
Finally, on reviewing whether a specific region of the brain is designated to face cells it seems likely that this is so, but that it may not be restricted to human faces. Instead, it seems probable that specific associations set in action the suitable responses. Moreover, rather than specific areas within the brain being allotted to face cells, there appears to be a visual pathway which runs along the occipitotemporal region. Words Count: 2, 103. Bibliography: Bauer, R. M. (1993).
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