only limited value in explaining face recognition and theoretical approaches specifically devoted to face recognition are needed.
Third, we now have a good understanding of the processes involved in face recognition. One reason for this is the diversity of research – it includes behavioural studies, studies on brain-damaged patients and neuroimaging studies.
prosopagnosia). Note that there appear to be few (or no) cases of pure prosopagnosia.
In spite of their poor conscious recognition of faces, prosopagnosics often show evidence of covert recognition (face processing without conscious awareness). For example, Simon et al. (2011) presented familiar and unfamiliar faces to a prosopagnosic, PS, who showed an absence of conscious recognition of the familiar faces. In spite of that, PS showed more activation in a brain area associated with face processing (the fusiform face area discussed later) when presented with familiar, but not unfamiliar, faces. Thus, familiar faces were processed below the level of conscious awareness.
IN THE REAL WORLD: HEATHER SELLERS
Up to 2% of the population suffer from prosopagnosia or face blindness. We can understand the profound problems they experience in everyday life by considering the case of Heather Sellers (see photo) (you can see her on YouTube: You don’t look like anyone I know). She is an American woman suffering from prosopagnosia who wrote about her experiences in a 2010 book entitled, You Don’t Look Like Anyone I Know. When she was a child, she became separated from her mother at a grocery store. When staff at the store reunited mother and child, Heather did not initially recognise her mother.
Note, however, that Heather Sellers does not have major problems with all forms of visual recognition: her ability to recognise objects is essentially normal.
Heather Sellers even has difficulty in recognising her own face. As a child, she found it very hard to pick out her own face in school photographs. As an adult, Heather Sellers admits, “A few times I have been in a crowded elevator with mirrors all round and a woman will move, and I will go to get out the way and then realise ‘oh that woman is me’.” Such experiences made her a very anxious person.
Surprisingly, Heather Sellers was in her mid-thirties before she realised she suffered from prosopagnosia. Why did it take so long? In essence, she identifies other people by relying on their hairstyle, body type, clothing, voice and gait. However, that has not prevented her from being severely embarrassed by her frequent failures to recognise people she knows well. She has also made friends angry by walking straight past them. Most surprisingly, she even failed on occasion to recognise her own husband! According to Heather Sellers, “Not being able to reliably know who people are – it feels terrible like failing all the time.”
Heather Sellers. © Patricia Roehling.
Why do prosopagnosics have very poor face recognition but reasonable object recognition? One explanation is that they have a face-specific recognition disorder involving damage to a brain area specialised for face processing. Another explanation is that face recognition is much harder than object recognition. Face recognition involves distinguishing among members of the same category (i.e., faces). In contrast, object recognition often only involves identifying the relevant category (e.g., cat, car). According to this viewpoint, prosopagnosics would perform poorly if required to make fine-grained perceptual judgements with objects.
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Prosopagnosia
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Video of a prosopagnostic
Findings
Busigny et al. (2010b) tested the two above explanations. The visual recognition performance of a male prosopagnosic patient, GG, was compared with that of healthy controls for several object categories: birds, boats, cars, chairs and faces. On each trial, participants were presented with a target stimulus belonging to one of these categories followed by two stimuli from the same category (target + distractor). The participants indicated the one seen previously.
The findings from this study are shown in Figure 3.12. GG was as accurate as the controls with each non-face category. However, he was substantially less accurate than controls with faces (67% vs. 94%, respectively). Thus, GG seems to have a face-specific impairment rather than a general inability to recognise complex stimuli.
Busigny et al. (2010a) found evidence from previous research suggesting at least 13 prosopagnosics had essentially normal levels of object recognition in spite of very poor face recognition. However, they identified two limitations with this research. First, the difficulty of the recognition decisions patients had to make was not manipulated systematically and is hard to assess. Second, the most informative approach is to measure the speed of recognition decisions as well as their accuracy. This had not been done in these earlier studies.
Busigny et al. (2010a) eliminated these limitations in their study of PS, a female prosopagnosic. They manipulated the similarity between target items and distractors on an object-recognition task and recorded reaction times as well as error rates. Increasing the degree of similarity between targets and distractors increased error rates to the same extent in PS and healthy controls. In contrast, PS performed very poorly on a face-recognition task even when it was very easy for healthy controls.
Figure 3.12
Accuracy and speed of object recognition for birds, boats, cars, chairs and faces by patient GG and healthy controls.
From Busigny et al. (2012b). Reprinted with permission from Elsevier.
Suppose face recognition and object recognition involve somewhat different brain areas. If so, we might expect to find patients with severely impaired object recognition but intact face recognition. There is some support for this expectation. Moscovitch et al. (1997) studied CK, a man with object agnosia (impaired object recognition). He performed as well as healthy controls on face recognition regardless of whether the face was a photograph, a caricature or a cartoon, provided it was upright and the internal features were in the correct places.
Why is face recognition so poor in prosopagnosics? A popular explanation is that they have great difficulty with holistic processing. Busigny et al.
(2010b) tested this explanation in experiments on the prosopagnosic GG in a study referred to earlier. GG did not show the face inversion or composite face effects. Thus, GG does not perceive individual faces holistically, an ability necessary for accurate perception of individual faces. In contrast, recognition of individual non-face objects does not require holistic processing, and so GG’s performance was intact with those objects.
Further evidence of deficient holistic processing of faces in prospopagnosics was reported by Van Belle et al. (2011). In one condition, observers could only see one part of a face at a time (e.g., eye, mouth) – this was done to restrict holistic processing. In this condition, the face-recognition performance of a prosopagnosic, GG, was comparable to that of healthy controls. As expected, GG performed much worse than healthy controls when the whole face was accessible and so holistic processing was possible.