Brain Activation Is Pretty Selective

Neuroimaging researchers like to talk about bits of the brain in terms of what kind of stimuli they respond to.

The "Fusiform Face Area (FFA)" and "Parahippocampal Place Area (PPA)" are two of the most popular of these 'clue is in the name' areas. The FFA lights up in response to seeing faces, while the PPA is more into places... so textbooks will tell you.

But how selective are these areas really? We know that the FFA activates more to faces than to other things on average, but is there overlap? Are there non-faces that activate the FFA more than many faces? Or perhaps, are there faces that don't activate the FFA? If there were, it would undermine the whole concept of the FFA as a "face area".

NIH researchers Marieke Mur et al have just examined this question and the results are out now in the Journal of Neuroscience. They show that yes, the FFA is selective for faces and likewise, the PPA is really pretty place-selective.

Which is a nice surprise. The last few weeks have been tough ones for brain scanning, with a crop of studies showing potentially serious flaws in popular neuroimaging methods. I was bracing myself for more bad news when I picked up this paper, but the results are actually quite reassuring.

They fMRI scanned 4 volunteers twice each, and showed them a series of 96 pics - some faces, some places, plus bodies and objects. They found that there was little overlap in the degree of activation across categories: few non-faces activated the FFA as strongly as faces - the closest were bodies, which are living things too so that makes sense. The PPA was even more selective.

See the picture at the top which shows stimuli ranked by how much they activated each area.

Fascinatingly - well, amusingly - the least face-like picture was some garlic, but the most unplaceish image was a cucumber.

Maybe these volunteers just didn't like vegetables.

There was some overlap between faces and non-faces for the FFA activations but it wasn't consistent. The second scan session - with the same 96 pics - found that those non-faces that activated the FFA the first time, didn't do so the second time. So it was just random noise.

Overall this is a lovely study, although it does underline the fact that although these areas are consistently selective, the difference is pretty subtle; there's no "break point". The FFA does prefer faces... but not enormously so.

Mur M, Ruff DA, Bodurka J, De Weerd P, Bandettini PA, and Kriegeskorte N (2012). Categorical, yet graded - single-image activation profiles of human category-selective cortical regions. The Journal of neuroscience : the official journal of the Society for Neuroscience, 32 (25), 8649-62 PMID: 22723705

Facial Expressions of Emotion Still Culturally Universal

Do people from different cultures express emotions differently?

A new paper says yes: Facial expressions of emotion are not culturally universal. But as far as I can see the data show that at least some of them very much are universal.

First some background. The authors, Rachael Jack and colleagues of Glasgow, have published before on this theme. Back in 2009 I blogged about one of their previous papers, which showed that East Asians were less accurate than Westerners at categorizing certain emotions.

But although there were cultural differences in ability to classify some emotions, East Asians still did much better than just guessing. To me, this said that there are fundamental universal emotional expressions, albeit culture can subtly modify them.

That's my verdict on this study as well.

The authors adopted a new (and very clever) method this time. Rather than just showing people photos of actors posing expressions, and asking subjects to label them with an emotion, they generated virtual faces using a 3D modelling software, and made the faces display "expressions", with their 41 virtual facial muscle groups.

Subjects (either white Westerners, or recent East Asian immigrants) saw 4,800 random assortments and had to label each one; the authors could therefore work back to calculate their "mental model" of that emotion based on the set of facial movements that best fit, individually (it reminds me of this method).

What happened? The Westerners mental models clustered into the classic 6 "basic emotions" of happy, sad, disgust, fear, anger, and surprise. The Asians however didn't; although they were pretty much the same on happy and sad, they were less clear about the other 4.

But how much less? Take a look:

Cluster analysis and dissimilarity matrices of the Caucasian and Asian models of facial expressions. In each panel, vertical color coded bars show the k means (k = 6) cluster membership of each model. Each 41-dimensional model (n = 180 per culture) corresponds to the emotion category labelled above (30 models per emotion). The underlying grayscale dissimilarity matrices represent the Euclidean distances between each pair of models, used as inputs to k-means clustering. Note that, in the Caucasian group, the lighter squares along the diagonal indicate higher model similarity within each of the six emotion categories compared with the East Asian models. Correspondingly, k-means cluster analysis shows that the Western Caucasian models form six emotionally homogenous clusters... In contrast, the Asian models show considerable model dissimilarity within each emotion category and overlap between categories.

This shows that yes, Asians "confused" some emotions more than Westerners but the basic emotional distinctions seemed to be intact, with Happy and Sad especially solid.

And look at these examples of the "mental model" for one subject of each group: yes they're different, but not very.

These are fine results, and I think there are real questions over whether the Ekman 6 emotions model really captures the essence of human emotions (especially negative ones.)

But, especially in the context of previous work from the same authors, I don't think these data really justify the paper's title ("Facial expressions of emotion are not culturally universal"), or the statement that

Our data directly show that across cultures, emotions are expressed using culture-specific facial signals. Although some basic facial expressions such as fear and disgust originally served as an adaptive function... facial expression signals have since evolved and diversified to serve the primary role of emotion communication during social interaction. As a result, these once biologically hardwired and universal signals have been molded by the diverse social ideologies and practices of the cultural groups who use them for social communication.

Overall, (ahem) I'm happy to admit that these data show some surprising cultural differences, but I'm afraid that the authors' overblown rhetoric makes me disgusted, sad and angry.

Jack, R., Garrod, O., Yu, H., Caldara, R., & Schyns, P. (2012). Facial expressions of emotion are not culturally universal Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1200155109

The Geography of Faces

How much can you tell about where someone comes from, just from their face?

The other day I was in London and came across a group of young people in Muslim attire who were waving (or in some cases wearing) a particular flag. I thought it was the Iranian flag, but, I thought, they didn't look Iranian. They looked more like Somalis, but it certainly wasn't the blue and white Somali flag. I decided that maybe they were some kind of pro-Iranian demonstrators, but I later worked out that it was the flag of the unrecognised state of Somaliland.

This got me thinking about how reliable these "they look they're from..." judgements are.

Clearly on a basic level, we can usually tell which continent someone's ancestors were from, in terms of the familiar "races" of Europeans, Africans, East Asians etc. But what about shorter distances?


Could you tell, just from looking at them (and setting aside dress, hairstyle, jewellery etc.) whether someone was from Spain as opposed to France? Korea or Japan? Russia or Germany?

I can only speak for England, but there's certainly a vague but widespread belief that every part of Europe has a  distinct 'look'. In the past, people were very fond of talking about that kind of thing; today, we're rather embarrassed by the idea but the belief lives on.

I don't know, but I'd be very surprised if there weren't analogous beliefs in other countries.

But how accurate are these folk beliefs, really?

Supposing you were the world expert on human faces - or suppose you were a supercomputer with face-recognition software and access to Facebook's entire dataset. How accurately could you place someone's origins on the map, on average? To within 1000 km? 100? With what degree of accuracy? In an ideal world, could the ultimate face-placer judge someone as French vs German 75% of the time? 90%? Or only slightly better than chance?

I suspect that if you researched this, you'd find that a supercomputer could do very well, in most parts of the world, but that the majority of actual people are less accurate than they think they are.

The Evolutionary Psychology of Race, Beauty and Marriage

There are some papers that you can tell are going to be hot potatoes just from the titles. This is one of them: A Facial Attractiveness Account of Gender Asymmetries in Interracial Marriage.

Coming so soon after The Unconquered World, you'd be forgiven for thinking I am taking this blog in a more linkbaiting direction because I'm planning to introduce ads. I'm really not, it's just a coincidence.

The paper claims that white women are on average more attractive than black, while East Asians are prettier still.  For men, however, the positions were reversed (and the effects were even stronger.)

Saying that black women are on average less attractive than others was what got evolutionary psychologist and blogger Satoshi Kanazawa into spot of bother last year. The current paper agrees with Kanazawa on that point (though doesn't cite him)... although it also declares Kanazawa to be part of the least attractive race for males, so I don't know how happy he'll be about it.

Author Michael B. Lewis of Cardiff University took 600 Facebook photos "from people who were members of groups associated with further and higher education bodies either in the UK (for White faces), sub-Saharan Africa (for Black faces) and East Asia (for Asian faces)."

Photos with a "weird expression" and people who "looked" under 18 or over 30 were excluded. The actual ages were not checked. Hmm.

A panel of 40 British students (half male) were asked to rate all of the opposite-sex faces for attractiveness from 1 to 10. The ethnicity of the rater made no difference to the results but there were only 5 black and 6 Asian students out of 40 though:

After this we get some models proposing how these data might relate to British and American inter-racial marriage patterns, and some evolutionary speculation regarding why this might have evolved - Asia was cold so men were in short supply, that kind of thing - but that's all assuming the basic data are solid.

There are many possible objections to the methodology here, some of which are addressed in the paper, but there's one massive that isn't -

It's not stated how the Facebook images were gathered. All we're told is that "a research assistant" got the images from higher education institutions. Were they, consciously or subconsciously, picking photos that fitted the expected some pattern?

We're not told whether or not this individual was aware of the hypothesis of the study when they chose the pics. If they were aware, it's a fatal confound; (Edit - 19th Feb 2012 - The paper in fact says that the research assistant was "naive" i.e. that they were not aware of the hypothesis of the study, which is of course sound methodology. I missed this statement in the first version of this post.)

However, the broader point remains that they might have been selecting in line with their own preferences, or some other bias. Clearly, there's much room for cherry picking the examples, based on whether they "looked" too young or old, or had a "weird" expression...

Link: Also blogged about here.

Lewis, M. (2012). A Facial Attractiveness Account of Gender Asymmetries in Interracial Marriage PLoS ONE, 7 (2) DOI: 10.1371/journal.pone.0031703

The Hidden Face Within

One of these two images contains a hidden picture of a face. Which one?

This was the question faced by participants in a remarkable psychology experiment just published, Measuring Internal Representations from Behavioral and Brain Data.

Five healthy volunteers were presented with a series of random black and white grid patterns. Each grid square was either black or white, and this was randomly determined on each trial.

There was no pattern to the images, they were completely random. But the subjects were told that half of the patterns contained a hidden face, and that their job was to work out which ones did. Each subject saw over 10,000 random images and they took about 1 second to judge each one.


The volunteers "detected" a face in 44% of the images. Somehow, all five of them convinced themselves that they were seeing faces in many of the grids. The authors say that

Upon completion of the experiment we debriefed observers, and all expressed shock that no face was ever presented.

That's strange enough in itself, but here's the really clever bit. The authors compared the patterns which were declared to contain a face, to the ones that were reported as empty. The image below shows the average "face" grid, minus the average "non face" grid, for each individual subject:

As you can see, this reveals...a face! Kind of. The top half shows the raw average; the bottom half shows the statistically significant differences from random noise.

In Subjects 1 and 2, the face is pretty clear, with eyes, a nose and a mouth. For 3 and 4, it's less coherent, but you might be able to see it if you look hard enough. For Subject 5, not really.

What this means is that people (at least, most of them) were not just seeing faces in any noise. They tended to see faces when the random patterns happened to resemble a kind of primitive face, but it was a different face for each person. The authors say that these strange faces correspond to the individual's internal representations, or models, of "a face", that each subject was "seeing" in the noise.

Finally, the whole experiment was conducted while EEG data was being recorded from the participant's brains. The EEG results revealed that there was a clear difference in the neural activity associated with "face" compared to "nonface" stimuli - except in Subject 5, who you'll remember had the least coherent "internal face".

What's exciting about this approach is that it investigates perception in a purely "top down" way. Normally, when we look at anything, what we end up perceiving is a product of "bottom up" influences - the raw data - and "top down" ones - what we expect to see. In this experiment, there was no real "bottom up" data; it was all "top down".

This is a form of pareidolia - perceiving familiar things in random stimuli. Seeing the face of Jesus in your sock, that kind of thing. It works for sounds too: in the famous White Christmas Experiment, people report "hearing" music in pure white noise - when told to expect it. Real-life examples of this include the "Islam Is The Light" doll, and my personal favorite, the singing paedophile Christmas mouse.

Finally, I wonder what embodied cognition theorists make of this paper. Because this paper claims to be "Measuring Internal Representations from Behavioral and Brain Data"; embodied cognition (at least the radical kind) is the theory that "internal representations" either don't exist, or at least don't explain anything about human cognition.

Smith, M., Gosselin, F., and Schyns, P. (2012). Measuring Internal Representations from Behavioral and Brain Data Current Biology DOI: 10.1016/j.cub.2011.11.061

The Face of a Mouse in Pain

Have you ever wanted to know whether a mouse is in pain?

Of course you have. And now you can, thanks to Langford et al's paper Coding of facial expressions of pain in the laboratory mouse.

It turns out that mice, just like people, display a distinctive "Ouch!" facial expression when they're suffering acute pain. It consists of narrowing of the eyes, bulging nose and cheeks, ears pulled back, and whiskers either pulled back or forwards.

With the help of a high-definition video camera and a little training, you can reliably and accurately tell how much pain a mouse is feeling. It works for most kinds of mouse pain, although it's not seen in either extremely brief or very long-term pain.

Langford et al tried it out on mice with a certain genetic mutation, which causes severe migraines in humans. These mice displayed the pain face even in the absence of external painful stimuli, showing that they were suffering internally. A migraine drug was able to stop the pain.

Finally, lesions to a part of the brain called the anterior insula stopped mice from expressing their pain. This is exactly what happens in people as well, suggesting that our displays of suffering are an evolutionary ancient mechanism. Of course this kind of study can't prove that animals consciously feel pain in the same way that we do, but I see no reason to doubt it: we feel pain as a result of neural activity, and mammals have exactly the same brain systems.

Langford, D., Bailey, A., Chanda, M., Clarke, S., Drummond, T., Echols, S., Glick, S., Ingrao, J., Klassen-Ross, T., LaCroix-Fralish, M., Matsumiya, L., Sorge, R., Sotocinal, S., Tabaka, J., Wong, D., van den Maagdenberg, A., Ferrari, M., Craig, K., & Mogil, J. (2010). Coding of facial expressions of pain in the laboratory mouse Nature Methods, 7 (6), 447-449 DOI: 10.1038/nmeth.1455

Neural Correlates of Being a Total Bad-Ass

A new fMRI study in PLoS reports Differential Brain Activation to Angry Faces by Elite Warfighters, the elite warfighters being US Navy SEALs.

SEALs are indeed pretty elite. This being a British blog, I wouldn't want to say that they're the world's elitest naval special forces unit. That's the British Special Boat Service. But they could still kill you ten times before you knew they were there (unless you're in the Special Boat Service.)

Anyway, San Diego researchers Paulus et al scanned 11 SEALs and 23 healthy civilian men during an emotional face matching (originally developed by Hariri et al) that involved seeing happy, angry, and fearful faces.

Such tasks are very popular in neuroimaging at the moment because looking at faces of people expressing strong emotions reliably activates emotion-related brain areas, without needing to actually induce emotions in your volunteers which can cause practical problems, i.e. people getting scared and maybe panicking in the MRI scanner. Whether studying emotional-face-induced activation is a valid substitute for studying emotion-induced activation is an open question.


What happened? fMRI being a sensitive way of measuring human brain activation, they found some differences between the two groups in neural responses to seeing the faces:

elite warfighters relative to comparison subjects showed relatively greater right-sided insula, but attenuated left-sided insula, activation. Second, these individuals showed selectively greater activation to angry target faces relative to fearful or happy target faces bilaterally in the insula.

OK. So what does that mean?

These findings support the notion that elite warfighters... deploy greater neural processing resources toward potential threat-related facial expressions and reduced processing resources to non-threat-related facial expressions. This finding suggests that rather than expending more effort in general, elite warfighters show more focused neural and performance tuning, such that greater neural processing resources are directed toward threat stimuli and processing resources are conserved when facing a nonthreat stimulus situation.

So the message is that SEALs are better at focusing on threats and don't get distracted by benign background stuff. Although apparently this is only true of their insula, not an area known for its role in attention, and the threat was an angry face on a screen. But that aside, this is not very surprising given that they're highly-trained soldiers.

But the unsurprisingness of this result is a problem. We don't need neuroscience to tell us that elite soldiers are good at detecting and responding to threats. That's rather obvious. I'd guess that most of them were pretty good at it before they got selected, and then they got even better with training. This must have something to do with the brain, because your brain is what allows you to learn stuff.

What we don't understand very well yet is how training (or other forms of learning) works, on a neural level, i.e. what the molecular and cellular mechanisms are. It would be really nice to find out. Unfortunately, fMRI studies like this are unable to tell us that, because they only study the very last stage in the process, the final product.

This is in no way a problem with this paper alone, and it's no worse than many other articles. The same issue applies to many neuroimaging studies of abnormal states like depression or, as I've posted about previously, psychological trauma. Such results can form the basis for investigations into mechanisms, and as ways of testing theories, but on their own, finding that abnormal brains react in abnormal ways is not, in itself, very useful.

Paulus, M., Simmons, A., Fitzpatrick, S., Potterat, E., Van Orden, K., Bauman, J., & Swain, J. (2010). Differential Brain Activation to Angry Faces by Elite Warfighters: Neural Processing Evidence for Enhanced Threat Detection PLoS ONE, 5 (4) DOI: 10.1371/journal.pone.0010096

Emotions are Still Universal

Are facial expressions of emotion culturally specific, or universal? For decades, the dominant view has been that they are universal, at least when it comes to a set of "basic" emotions: fear, happiness, sadness, surprise, anger, and disgust.

Darwin was an early proponent of the idea that all humans (and indeed other mammals) display emotions in certain ways; his book The Expression of the Emotions in Man and Animals is still a very interesting read.

More recently, the universalist view has been closely associated with the psychologist Paul Ekman. In the 1960s Ekman reported that people from diverse cultures, including isolated tribespeople from Papua New Guinea, make similar faces in response to similar situations.

Now, a new paper claims that Cultural Confusions Show that Facial Expressions Are Not Universal. This article has got a lot of media and blog attention, not surprisingly, since at least judging by the title, this is a major upset.

But the paper's findings are rather modest. The authors, Jack et al, took 13 white British and 13 East Asian subjects. The Asians, who were mostly from China, had only been in Britain for about a week, and all subjects reported that they had never lived in, or even visited an "other race" country, dated interracialy, etc.

Subjects were shown pictures of faces and had to pick the appropriate "basic emotion" - anger, disgust, fear, happy, neutral, surprise, and sadness. The faces were of actors posing the emotions, in accordance with Ekman's "FACS" system.

The result was that Western subjects did well on all emotions, but the Asians did less well on fear and digust, as they tended to confuse these two emotions. The authors also used eye-tracking technology to see where the subjects were looking, and found that the East Asians tended to focus on the eyes more while examining the faces, which may explain their differing performance.

This is quite interesting, especially the eye-tracking data (which goes into a lot of detail). But does it justify the conclusion that:

Our data demonstrate genuine perceptual differences between Western and East Asian observers and show that FACS-coded facial expressions are not universal signals of human emotion. From here on, examining how the different facets of cultural ideologies and concepts have diversified these basic social skills will elevate knowledge of human emotion processing from a reductionist to a more authentic representation. Otherwise, when it comes to communicating emotions across cultures, Easterners and Westerners will continue to find themselves lost in translation.

Well, sort of, but the differences found in this study were really rather small. Statistically, the Asians successfully recognized fear and disgust less often than the Westerners. But they still got them right 58% and 71% of the time, respectively, even when the faces were Western; they did better when the faces were Asian. Given that there were 7 options, had they been picking randomly they would only have got 14% right. 58% is still pretty good. The Asians were actually (non-significantly) better at recognizing neutral, surprised, and sad faces.

And the differences notwithstanding, the whole task relies upon the fact that the subjects know the meaning of "happy", "fear", and so forth, and associate them with certain face expressions. The fact that the experiment worked at all shows - as Ekman would predict - that both Westerners and East Asians share an emotional understanding. There appear to be some cultural quirks, but the essential universality of facial emotion still stands.

Jack, R., Blais, C., Scheepers, C., Schyns, P., & Caldara, R. (2009). Cultural Confusions Show that Facial Expressions Are Not Universal Current Biology DOI: 10.1016/j.cub.2009.07.051

Special issue on the Neuropsychology of Faces

Just a tip-off: if you liked my discussion of the brain and faces, you'll love the latest issue of the Journal of Neuropsychology.

Are Faces Special?

There's been a glut of face-based science lately. There was the first American face transplant (the second if you count the ill-fated Travolta/Cage one...) Then an Atlanta group allegedly found that chimpanzees have a part of the brain specialized for recognizing the faces of their fellow chimps.

As I'll explain, this would be extremely important if true. This research is just the latest chapter in a long and contentious debate going back many years - a debate which, believe it or not, may hold the answer to Life, the Universe, and Everything! I'll get onto that later.

The human brain may, or may not, have regions which are "hard-wired" specifically for the visual processing of faces; the question of whether it does is generally known as the "Are Faces Special?" debate.(*) The majority of neuroscientists today would say that yes, they are, and that yes, we do have at least one such face area. I agree with this, but the debate's not yet ever - although as usual the reporting on this study glosses over such complexities.

On the face of it (ha), the evidence for specialized processing of faces in the human brain is very strong. We're very good at distinguishing and recognizing faces, despite the fact that they are all extremely similar - and when faces are shown upside-down, we are much worse at dealing with them. This suggests, to most people, that we have a specialized capacity for processing faces.

Following certain brain lesions, some patients lose their ability to recognize faces, a condition known as prosopagnosia. This most commonly follows damage to a part of the temporal lobe of the brain called the fusiform gyrus. Prosopagnosics may be able to identify and recognize other kinds of objects, but they just can't "get" faces. (Prosopagnosia can also be congenital i.e. present from birth). To a prosopagnosic, every face is as inscrutable as upside-down faces are to the rest of us.

Meanwhile, neuroimaging has consistently shown a small portion of the aforementioned fusiform gyrus on the right side, dubbed the "fusiform face area (FFA)", is more activated when people are looking at pictures of faces than when they are looking at inanimate objects, other body parts, or pictures of faces which have been scrambled up so as to no longer look like faces.

So all of the evidence seems to mesh together ("converge") splendidly: there's a face area in the human brain, located in the Fusiform Face Area, which is responsible for our unusually good face-processing abilities. Hurrah. However, there's a parade-raining alternative view, namely that faces are not special, we are only good at processing them because we have so much experience doing so, and the FFA's role lies in detecting the differences between similar objects about which we have learned to be highly familiar - faces being just one example.

The details of this debate are fairly bewildering. For what it's worth, the "expertise" account has always seemed rather contrived to me and expertise theorists seem to be on the defensive against the more confident and plausible "specialist" neuroscientists. But that's just my opinion. For an excellent overview of the neuroscience of faces see here; for a skeptical view of the Fusiform Face Area see this; for skepticism of the skepticism here.

Anyway, into this debate stepped Lisa Parr et. al. who used ¹⁸F-flurodeoxyglucose PET imaging to measure neural activity in five adult chimpanzees. Their goal was to see whether chimps possess a Fusiform Face Area or not. Chimps, unlike "lower" monkeys, are good at recognizing chimp (and human) faces. The five luckless chimps had to perform two tasks, one of which involved visually "matching" pictures of chimp faces in order to earn Kool-Aid. The other control task involved the same procedure but with matching non-face pictures ("Clip Art").

Subjects have been trained to control the movements of a cursor on the computer screen by manipulating the joystick ... At the beginning of a trial, a single image (the sample) appears on the computer screen on a black background. ... After this, the sample clears the screen and two comparison images appear on the monitor ... One of these comparisons matches the sample (the target), and the other (the foil) is a different image from the same category, either another face or another clip art object. ... Subjects must contact the image that matches the sample by contacting it with the joystick-controlled cursor.

Compared to the control Clip Art task, the chimp's brains were more active during the face task in a wide range of areas. The most "face-selective" area was the "Dorsal primary motor/medial parietal cortex (Left)" which has nothing to do with faces, vision, or any of that kind of stuff. The authors try to put a brave face on this (emphasis mine)...

The first [whole brain] analysis revealed numerous brain regions that showed greater metabolic activity during the face-matching task when compared directly to the object-matching ... [including] the posterior superior temporal sulcus (STS) and orbitofrontal cortex ... These regions comprise part of the distributed cortical network for face processing in humans. Notably absent from this analysis was activity in the fusiform gyrus, the primary region where face-selective activity is found in humans when the comparable analysis is used.

...but this is clearly a disappointing result. No chimp FFA found. Yet this is hardly surprising, considering that there were only five subjects in this experiment, and there's obviously a big difference between a human volunteer, and a chimpanzee who's spent years being experimented on, is locked in a cage, is highly trained on the computerized task, and who is doing the experiment for Kool-Aid.(**) The absence of evidence in this experiment is not evidence of absence.

All was not lost, however, because the authors then did a different analysis, looking for individual voxels (small parts of the brain) which were "face selective" or "object selective". (I suspect this was a post-hoc analysis, a naughty practice which I have warned about before, but here it's arguably OK). Short story - they found a lot of such voxels, most of them in areas which are nothing to do with faces or vision, but there were quite a few in the fusiform gyrus, which is where you might expect them to be based on human work (see above.) But honestly, neuroimaging data is noisy enough at the best of times and with just five subjects it's virtually impossible to draw any conclusions. A human PET study with n=5 would never get published; by the standards of chimp research n=5 is big because chimps are much harder to work with. Personally, I'm just glad I don't work with chimps.

What about Life, the Universe, and Everything? Well, the "Are Faces Special" debate is relevant to such cosmic questions (almost), because it's one aspect of the great "modularity" debate, which is basically psychologists and neuroscientists debating the existence of human nature. If humans are genetically programmed to have a part of the brain (a "module") specialized for processing faces, presumably this is because we evolved to do so. If so, then this makes it very plausible that other parts of our brains evolved for such specialist purposes, and this implies that our minds work in certain ways because of evolution (i.e Evolutionary Psychology) and that human nature is largely fixed.

On the other hand, if faces aren't special, maybe nothing is - maybe there is no such thing as human nature and all our behavior is learned by experience. That would imply that culture and history are much more important than biology in understanding human life, and that with sufficient political and social advancement anything is possible! Wow. That's the importance of neuroscience. At least, that's what neuroscientists will tell you when they want you to give them money or buy their books...

(*) If you're at a cognitive neuroscience conference and feel like a slap in the face, try opening a conversation with a pretty young grad student with the line "I don't know if faces are special, babe, but yours is".
(**) Although given the state of some undergrads, the differences might not always be in the human's favor.

L PARR, E HECHT, S BARKS, T PREUSS, J VOTAW (2008). Face Processing in the Chimpanzee Brain Current Biology DOI: 10.1016/j.cub.2008.11.048