Wednesday, November 24, 2010

Gladly Making An Exception

Like Groucho Marx, some people never forget a face.* I, on the other hand, seldom recall one, or at least not right away. Several introductions are usually required before I can properly recognize somebody. I can talk to a new person directly for a decent length of time, at a job interview for instance, and then fail to recognize them when I pass them on the street the next day. As you can imagine, it’s a bit embarrassing. The list of social faux pas I’ve made as a result of this problem is lengthy and often absurd. Most famously, I once tried to strike up a conversation with a guy I’d already been on a date with. Even after he politely told me that we’d already met, it took me a few minutes to place where I’d last seen him. In my defense, he’d changed his hair…well, or maybe just his coat. Something. Whatever detail had been disrupted instantly rendered him a stranger to me. In a more practical social universe, everyone would have dramatic features or distinguishing accessories that they always wore. Better still, they would each just wear the same outfit every day, because it is far easier to identify a shirt than a face.

My difficulty recognizing faces is relatively mild. I can eventually commit a new face to memory, it just takes a frustratingly long time. But there are those for whom the situation is far worse. In 1947 neurologist Joachim Bodamer introduced the term prosopagnosia to describe the inability to identify faces. The condition, which also goes under the more pronounceable nickname “face blindness”, can be so severe that those afflicted with it struggle to recognize life-long friends, family members or even their own faces in the mirror. Like most of the exotic maladies I opt to write about, prosopagnosia is not especially common, affecting perhaps 1 or 2% of the population. However, researchers have only recently started paying attention to milder forms of face blindness, so it’s difficult to say how many more people like me are walking around oafishly ignoring acquaintances at the grocery store and inadvertently snubbing potential employers.

AP vs. CP
Face blindness comes in two flavors. Acquired prosopagnosia (AP) was the first to be described and, as its name suggests, is brought on by some sort of calamity (often a stroke or a head injury) after any number of years of prior normal face recognition. Congenital prosopagnosia (CP) begins at birth and seems to run in families. There are some curious differences between the 2 variations. Notably, individuals with AP have been found to have abnormal FFA activity when viewing faces. CP individuals however generally exhibit no FFA abnormalities when subjected to similar tests. “This would be fascinating,” You’re thinking, “if I actually had any idea what the FFA was.”

What The FFA
In reality you’ve probably heard of this already, though perhaps not by its proper name. The letters stand for Fusiform Face Area, but the person who told you about it at a party may have called it by some approximation such as, “that special face part of the brain”. The FFA is a region of the visual cortex thought to be specialized for the processing of face images. fMRI brain imaging has shown the FFA to be more active in subjects when viewing faces than when viewing various other objects and body parts (namely human hands). Since first being described in the 1990s, the function of the FFA has been debated, with some studies showing that it is also active during the viewing of non-face objects by viewers who are “experts” in these objects (automobile enthusiasts looking at cars, bird-watchers looking at birds, etc.). But face stimuli continue to elicit strong FFA responses in normal subjects and thus brain imaging of this region is a must for any self-respecting experiment hoping to shed light on prosopagnosia.†

Don’t bother looking it up. No reasonable dictionary or spell check would except “faceness” as a word. It’s just the folks in the laboratory playing with neologisms again. What they’re trying to convey with this term is the nebulous quality that can make a non-face object appear face-like. Humans excel at finding face imagery in objects that are in no way related to faces of our species or any other. Clusters of shapes that evoke faces are almost suspiciously ubiquitous. People see faces in clouds and wood grain and rock formations. They see a man on the moon and the Virgin Mary on a grilled cheese sandwich.‡ The reported prevalence of car-shapes or chair-shapes in abstract patterns is much lower. Clearly there is something special about the structure of a face. Not only are we prone toward perceiving face-shapes, but the FFA in more active when viewing objects with higher levels of “faceness”, even though it is well understood that they are not actual human forms. Unless you suffer from severe face blindness, your own FFA probably lit up when it saw the 3 electrical outlets used to dress up this article (and would have done so even had I not added facial expressions to them). What is it about such shapes that so readily captures your imagination? Without going into a lot of evolutionary speculation as to the benefit of being able to spot a face, I can relay to you experimental findings of what kinds of shapes get the most FFA response. They are symmetrical shapes with more elements in the upper portion than the lower portion. Basically something approximating 2 eyes on top and 1 mouth on the bottom, like so…   ^_^

Trees vs. Forests
There is some speculation that congenital prosopagnosia (CP) may be associated with deficiencies in global processing. Certain patterns can be viewed on a global and local level. A common experimental model of global vs. local perception is nested letters, in which larger letters are built out of smaller ones. These can be built using matching or non-matching nested letters.

Normal subjects tend to identify both global and local elements more quickly when they are matched (a large letter F made from small letter Fs, rather than from small letter Ts). With unmatched nested letters, global information can interfere with processing of local information and vice versa. In such cases, normal subjects are faster at spotting the global shapes (big letters) than the local shapes (smaller nested letters). The reverse trend has been observed in some individuals with CP. Not only did these subjects have more trouble spotting the large letters in the non-matched nested-letter stimuli than those in the control group (individuals with normal ability to recognize faces), but they were actually faster than the control group at identifying the smaller local letters, even in the non-matched scenarios. It is as though people with CP barely notice the global pattern and instead make a beeline for the interior details. In a face, the local elements are individual features - eyes, nose, mouth – while the global element is the entire face. Recognizing a face relies more on noting the configuration of the parts within the whole (are the eyes set wide or narrow, is the chin long or short) than on scrutinizing the parts. Thus people with CP may be missing the global face by getting mired in the details of its features.

Identification vs. Expression
Another curious difference observed between people with acquired (AP) and congenital (CP) prosopagnosia is the ability or lack thereof to accurately perceive facial expressions. Individuals with AP are often as unable to recognize the expression on a face as they are its identity.  However, some CP individuals have been documented to perform as well as the control group on facial expression tasks while still being completely hopeless in facial identification tasks. What this means in day-to-day life is that while they might be able to spot that a face is angry, they still won’t be able to tell who the face belongs to. However, given that the mystery face may well be that of a friend or acquaintance, they should at least have a good guess as to why it is angry.

What About Me?
If the symptoms I’ve been describing sound distressingly familiar, it is possible that you may be afflicted with some degree of prosopagnosia. Unfortunately it’s a bit harder to test for face blindness than for colorblindness. Probably you should be talking to a neurologist, but if you’re like me (short on time and money) you might prefer to take your chances with the internet instead. I found an online test that was quick and painless enough. Though loudly proclaiming that it can’t actually diagnose you, it does offer some vague quantification in the form of a score and numbers indicative of normal vs. impaired facial recognition performance. Stunningly I got a 66, which puts me below average (71) but still well above impaired (47). Perhaps there’s hope for me after all.

What’s a person to do if they score closer to a 47? Not a whole lot, I’m afraid. Intentionally or not, individuals with face blindness often rely on non-face cues to help sort out who’s who. Hairdos, glasses, and style of clothing often do the trick (or at least until their wearers suddenly decide they need a new look). Mannerisms, voices and context help too (your professor is the one in the front of the class, your neighbor is the one in the adjacent lawn, etc). From my own experience I would offer that, especially if you’re female, smiling politely at anyone who smiles at you first is not always the best strategy. Though if someone addresses you by name, there’s a good chance you’ve met them, so just roll with it.

As for the rest of you (the 71 and over scorers), my apologizes if I didn’t say hello when you saw me at the movie theater last weekend. It’s nothing personal. You might consider getting yourself some sort of accessory that makes you more readily recognizable, like an eye patch or a cane or an electric blue feather boa. It would really help me out.

* The oft-repeated quote is, “I never forget a face, but in your case I’ll be glad to make an exception.” I have no idea which film (if any) it came from. I’m not a Marx brothers fanatic, I’ve just heard the quote here and there.

† Another brain region, the Occipital Face Area (OFA), also figures prominently into such studies. However, I already have far too many details to cram into one little article.

‡ The Virgin Mary sammich came into existence in 1994 but is predated by nearly 2 decades by Maria Rubio’s pioneering Jesus tortilla. For a while, the latter could be viewed at a shrine in New Mexico. However, since both the tortilla and the grilled cheese look like fairly non-descript faces rather than specific religious figures, you can probably just make your own lunchtime miracle using whatever is currently in your fridge.

Who told you this?

Kanwisher, N. et al. 1997. “The Fusiform Face Area: A Module in Human Extrastriate Cortex Specialized for Face Perception.” The Journal of Neuroscience 17: 4302-4311.

Tarr, M.J. and Gauthier, I. 2000. “FFA: a flexible fusiform area for subordinate-level visual processing automatized by expertise.” Nature Neuroscience 3: 764-769.

Caldara, R. and Seghier, M. 2009. “The Fusiform Face Area Responds Automatically to Statistical Regularities Optimal for Face Categorization.” Human Brain Mapping 30: 1615-1625.

Bentin, S. et al. 2007. “Too Many Trees to See the Forest: Performance, Event-related Potential, and Functional Magnetic Resonance Imaging Manifestations of Integrative Congenital Prosopagnosia.” Journal of Cognitive Neuroscience 19: 132-146.

Schiltz, C. et al. 2006. “Impaired Face Discrimination in Acquired Prosopagnosia Is Associated with Abnormal Response to Individual Faces in the Right Middle Fusiform Gyrus.” Cerebral Cortex 16: 574-586.

Humphreys, K. et al. 2007. “A detailed investigation of facial expression processing in congenital prosopagnosia as compared to acquired prosopagnosia.” Experimental Brain Research 176: 356-373.

Love, B.C. et al. 1999. “A Structural Account of Global and Local Processing.” Cognitive Psychology 38: 291-316.

1 comment:

  1. Hi Alex! This is really interesting! I'm actually doing my masters thesis in grad school about prosopagnosia. I'd love to talk to you more about this. My email address is :)