The Best American Science and Nature Writing 2011 (49 page)

But while visual agnosia of a general sort was recognized in the 1890s, there was little notion that there could be agnosia for particular visual categories, such as faces or places, until 1947, when Joachim Bodamer, a German neurologist, described three patients who were unable to recognize faces but had no other difficulties with recognition. It seemed to Bodamer that this highly selective form of agnosia needed a special name—it was he who coined the term "prosopagnosia"—and that such a specific loss must imply that there was a discrete area in the brain specialized for face recognition. This has been a matter of dispute ever since: is there a system dedicated only to face recognition, or is face recognition simply one function of a more general visual-recognition system? A 1955 paper by the English neurologist Christopher Pallis, with beautiful detail and documentation, brought the issue to the fore.

Pallis's patient, A. H., was a mining engineer at a Welsh colliery who had kept a journal and was able to give Pallis an articulate and insightful description of his experiences. One night in June 1953, A. H. apparently suffered a stroke. He "suddenly felt unwell after a couple of drinks at his club." He appeared to be confused and was taken home to bed, where he slept poorly. Getting up the following morning, he found his visual world completely transformed, as he reported to Pallis:

I got out of my bed. My mind was clear but I could not recognize the bedroom. I went to the toilet. I had difficulty in finding my way and recognizing the place. Turning round to go back to bed I found I couldn't recognize the room, which was a strange place to me.

I could not see colour, only being able to distinguish light objects from dark ones. Then I found out all faces were alike. I couldn't tell the difference between my wife and my daughters. Later I had to wait for my wife or mother to speak before recognizing them. My mother is 80 years old.

I can see the eyes, nose, and mouth quite clearly but they just don't add up. They all seem chalked in, like on a blackboard.

***

Since Pallis's time, a number of patients with prosopagnosia have come to autopsy. Here the data are clear: virtually all patients with prosopagnosia, irrespective of the cause, have lesions in the right visual-association cortex, in particular on the underside of the occipitotemporal cortex. There is nearly always damage in a structure called the fusiform gyrus, and these autopsy results gained additional support in the 1980s, when it became possible to visualize the brain of living patients by CT scanning and MRI—here, too, prosopagnosic patients showed lesions in what came to be called the "fusiform face area."

In the 1990s, such lesion studies were complemented by functional imaging—visualizing the brains of people with fMRI as they looked at pictures of faces, places, and objects. These functional studies demonstrated that looking at faces activated the fusiform face area much more strongly than looking at other test images did.

That individual neurons in this area could show preferences was first demonstrated in 1969 by Charles Gross, using electrodes in the inferotemporal cortex of macaques. Gross found cells that responded dramatically to the sight of a monkey's paw—but also, less strongly, to a variety of other stimuli, including a human hand. Subsequently, he found cells that had a relative preference for faces.

Much that we now take for granted in neuroscience was very unclear when Gross began this work. Even in the late 1960s, it was widely believed that the visual cortex did not extend far beyond its main locus in the occipital lobes (as we now know it does). That the representation and recognition of specific categories of objects—faces, hands, and so on—might rely on individual neurons or clusters of neurons was considered improbable, even absurd; the idea was good-humoredly mocked by Jerome Lettvin in his famous comments about "grandmother cells." Very little attention, therefore, was paid to Gross's early findings, and it was not until the 1980s that they were confirmed and amplified by other researchers.

In humans, some ability to recognize faces is present at birth or soon after. By six months, as Olivier Pascalis and colleagues have shown in one study, babies are able to recognize a broad variety of individual faces, including those of another species (in this study, pictures of monkeys were used). By nine months, though, the babies had become less adept at recognizing the monkey faces unless they had received continuing exposure to them. As early as three months, infants are learning to narrow their model of "faces" to those they are frequently exposed to. The implications of this work for humans are profound. To a Chinese baby brought up in his own ethnic environment, Caucasian faces may all, relatively speaking, "look the same," and vice versa. One prosopagnosic acquaintance, born and raised in China, went to Oxford as a student and has lived in the United States for decades. Nonetheless, he tells me, "European faces are the most difficult—they all look the same to me." It seems that there is an innate and presumably genetically determined ability to recognize faces, and this capacity gets focused in the first year or two, so that we become especially good at recognizing the sorts of faces we are likely to encounter. Our "face cells," already present at birth, need experience in order to develop fully.

 

The fact that many (though not all) people with prosopagnosia also have difficulty recognizing places has suggested to some researchers that face and place recognition are mediated by distinct but adjacent areas. Others believe that both faculties are mediated by a single zone that is perhaps oriented more toward faces at one end and toward places at the other.

The neuropsychologist Elkhonon Goldberg, however, questions the whole notion of discrete, hardwired centers, or modules, with fixed functions in the cerebral cortex. He feels that at higher cortical levels there may be much more in the way of gradients, where areas whose function is developed by experience and training overlap or grade into one another. In his book
The New Executive Brain,
Goldberg speculates that a gradiential principle constitutes an evolutionary alternative to a modular one, permitting a degree of flexibility and plasticity that would be impossible for a brain that is organized in a purely modular fashion.

While modularity, he argues, may be characteristic of the thalamus—an assemblage of nuclei with fixed functions, fixed inputs and outputs—a gradiential organization is more characteristic of the cerebral cortex, and becomes more and more prominent as one ascends from primary sensory cortex to association cortex and, finally, to the highest level of all: the frontal cortex. Modularity and gradients may thus coexist and complement one another.

Some researchers have proposed that prosopagnosia is not purely a problem with face blindness but one aspect of a more general difficulty in distinguishing the individuals in any class, whether that class consists of faces, cars, birds, or anything else.

Isabel Gauthier and her colleagues tested a group of car experts and a group of expert birders, comparing them with a group of normal subjects. The fusiform face area, they found, was activated when all the groups looked at pictures of faces. But it was also activated in the car experts when they were asked to identify particular cars, and in the birders when they were asked to identify particular birds. The fusiform face area is tuned primarily for facial recognition, it seems, but some of it can be trained to distinguish individual items of other sorts. (If, then, an expert bird spotter or car buff is unlucky enough to acquire prosopagnosia, he will also, we might suspect, lose his ability to identify birds or cars.)

The fusiform face area does not work in isolation; it is a vital node in a cognitive network that stretches from the occipital cortex to the prefrontal area. Face blindness may occur even with an intact fusiform face area, if the lower occipital face areas have been damaged. And people with moderate prosopagnosia, like Jane Goodall or me, can, after repeated exposure, learn to identify those they know best. Perhaps this is because we are using slightly different pathways to do so, or perhaps, with training, we can make better use of our relatively weak fusiform face areas.

 

Above all, the recognition of faces depends not only on the ability to parse the visual aspects of a face—its particular features and their overall configuration—and compare them with others but also on the ability to summon the memories, experiences, and feelings associated with that face. The recognition of specific places or faces, as Pallis emphasized, goes with a particular feeling, a sense of association and meaning. While purely visual recognition of faces is mediated by the fusiform face area and its connections, emotional familiarity is probably mediated at a higher, multimodal level, where there are intimate connections with the hippocampus and the amygdala, areas that are involved in memory and emotion. Thus A. H., after his stroke, lost not only his ability to identify faces but also this sense of familiarity; every face and place appeared new to him and continued to do so even if seen again and again.

Recognition is based on knowledge, and familiarity is based on feeling, but neither entails the other. The two have different neural bases and can be dissociated; thus, although both are lost in tandem with prosopagnosia, one can have familiarity without recognition or recognition without familiarity in other conditions. The former occurs in instances of déjà vu and also in the "hyperfamiliarity" for faces described by Devinsky. Here a patient may find that everyone on the bus or in the street looks "familiar"—he may go up to them and address them as old friends, even while realizing that he cannot possibly know them all. My father was always very sociable and could recognize hundreds or even thousands of people, but his feeling of "knowing" people became exaggerated, and perhaps pathological, as he moved into his nineties. He often attended concerts at Wigmore Hall, in London, and there, during the intermission, he would accost everyone in sight, saying, "Don't I know you?"

The opposite occurs in people with Capgras syndrome, for whom faces, though recognized, no longer generate a sense of emotional familiarity. Since a husband or wife or child does not convey that special warm feeling of familiarity, the Capgras patient will argue, they cannot be the real thing—they
must
be clever impostors, counterfeits. People with prosopagnosia have insight; they realize that their problems with recognition come from their own brains. People with Capgras syndrome, in contrast, remain immovable in their conviction that they are perfectly normal and it is the other person who is profoundly, even uncannily, wrong.

 

Individuals with acquired prosopagnosia, like A. H. or Dr. P., are relatively rare—most neurologists are likely to encounter such a patient once or twice in their career, if at all. Congenital prosopagnosia (or, as it is sometimes called, "developmental" prosopagnosia), such as I have, is much more common, yet it remains completely unrecognized by most neurologists. This is not entirely surprising, for people with congenital prosopagnosia do not generally consult neurologists about their "problem." It is just the way they are.

Ken Nakayama, at Harvard, who investigates visual perception, has long suspected that prosopagnosia is relatively common but underreported. In 2001 he and his colleague Brad Duchaine, at University College, London, began seeking subjects with face blindness through their website, and they received an impressive response. Nakayama and Duchaine are now investigating several thousand people with lifelong prosopagnosia, ranging from mild to cripplingly severe.

While congenital prosopagnosics do not have gross lesions in the brain, a recent study by Garrido and colleagues showed that they do have subtle but distinct changes in the brain's face-recognition areas. The condition also tends to be familial: Duchaine, Nakayama, and their colleagues have described one family in which ten members—both parents and seven of their eight children (the eighth could not be tested), as well as a maternal uncle, have it. Clearly, there are strong genetic determinants at work here.

Nakayama and Duchaine have explored the neural basis of face and place recognition, generating new knowledge and insights at every level from the genetic to the cortical. They have also studied the psychological effects and social consequences of developmental prosopagnosia and topographical agnosia—the special problems these conditions can create for an individual in a complex social and urban culture.

And the range seems to extend in a positive direction, too. Russell, Duchaine, and Nakayama have described "super-recognizers," people with extraordinarily good face-recognition abilities, including some who seem to have indelible memories of virtually every face they have ever seen. Alexandra L., one of my correspondents, described her own uncanny ability to recognize people:

It happened again yesterday. I was on my way down into the subway in Soho when I identified someone fifteen feet ahead of me (back turned, talking intimately with his friend) as a man I knew, or had seen before. In this case, it was Mac, who used to be a family friend's art dealer. I had last seen him (briefly) two years earlier, at an opening in midtown. I'm not sure I've ever spoken with him beyond an introduction a good ten years ago.

This is an integral part of my life—I catch a passing glimpse of someone and, with no real effort,
flash,
place the face—yes, that's the girl who served us wine at an East Village bar last year (again, in a totally different neighborhood, and at night not during the day). It is true that I'm a big fan of people, of humanity and diversity ... but to my knowledge I make no effort to record the physical traits of ice cream servers, shoe salesmen and friends of friends of friends. Even a slim wedge of face, or the way someone walks two blocks away at dusk, can trigger my mind to zero in on a match.

The super-recognizers, Russell and colleagues write, "are about as good at face recognition and perception as [lifelong] prosopagnosics are bad"—that is, about two or three standard deviations above average, while the most severe prosopagnosics have face-recognizing abilities two or three standard deviations below average. Thus the difference between the best face recognizers and the worst among us is comparable to that between people with an IQ, of 150 and those with an IQ of 50. As with any bell curve, the vast majority are somewhere in the middle.