June
24
When shown a picture of a middle-aged male…
When shown a picture of a middle-aged male actor, how is it that we can easily tell Matt Damon from Mark Wahlberg? The actual differences in their faces are not huge in absolute terms, though it feels obvious when looking at them. Faces are all pretty much the same: two eyes, a mouth, a nose, a chin. What separates these two actors is many small differences; a centimeter difference between eye placement, one’s nose might be half-a-centimeter wider, maybe their cheekbones differ by some small amount. As social creatures, we seem to have an inborn talent for processing this particular pattern and can use subtle differences to instantly recognize which face we are perceiving. The field of research into visual processing of faces is extremely broad, as there are many interesting questions to be answered.
First off, do animals have face recognition? Much of the research in this field has been done in monkeys, and it appears they are adept face perceivers as well. But what about something as remote from humans as a wasp? An interesting study found that a social species of wasps could detect subtle differences between wasp facial patterns, while a non-social wasp species was unable to perform the task1. This and other evidence suggests that facial processing is foundational to being a social species. After all, how can you properly socialize with members of your species if you can’t tell which one you’re interacting with?
This brings us to a second point, how crippling it would be if we lost the ability to recognize faces. This condition is called ‘prosopagnosia’. For the most part, patients with this condition have a normal visual experience; they can see all the parts of the face, but the mechanism in the brain which usually knits them together in the experience of ‘faceness’ is either absent or malfunctioning. One man (Chuck Close2) who has this condition has actually tried to overcome it by becoming a master face artist. His approach is to break the face down into very small ‘quadrants’ and then draw exactly what he sees in that quadrant. Interestingly, he may actually have an advantage over the rest of us in his drawings, because it is very difficult for me (and probably you) to focus on a quadrant of a face without seeing it as a constitutive whole.
Since people with prosopagnosia have otherwise normal vision, we can deduce that the part of the brain that processes these facial patterns must be distinct from the part of the brain that performs basic visual processing. In research with both monkeys and humans, a wide ‘face network’ of regions have been implicated including the inferior temporal cortex, lateral occipital cortex, middle temporal gyrus, amygdala, and various subcortical structures including the pulvinar3,4. Typically, people with prosopagnosia have damage to the fusiform gyrus (in the inferior temporal cortex). But why do we devote so much area in the brain to something so simple? The answer is that there is actually a lot to do when processing faces. We have to be able to recognize the object we are looking at is a face and then recognize whether it is someone we may not have seen for decades. Then we have to instantly intuit how they feel about seeing us (are they angry, sad, happy?). And to do all this we have to know that their face is the same object no matter if we only see only part of it from the right or the left, top or bottom. Our brain is capable of some pretty amazing things, and our ability to process all the aspects of a face at fast speeds is one of those capabilities.
Earlier I made the statement that facial processing was an ‘inborn talent’. Now that’s actually a somewhat contentious statement. Some people believe that parts of our brain are pre-determined to be able to quickly and accurately process faces5. Others believe we gain this ability over time because we spend so much of our lives looking at faces6. One study attempted to answer this question by keeping newborn monkeys from seeing faces for up to 2 years7. The fascinating outcome of this study is that initially, these monkeys were impaired in face processing, but after as little as one month they were able to catch up and perform facial processing tasks at the same level as monkeys who had spent their whole life seeing faces! This suggests that while we may not be able to process faces expertly from the moment we are born, we have a strong predisposition from birth to learning the patterns of faces.
Anyway, thanks for your attention! I hope that something in here has piqued your interest. The papers I’ve listed below in the references are a good jumping off point into further literature on the subject. If you are interested at all in autism, I have included a bonus reference8 exploring the relationship of oxytocin & face processing with this condition (but that is a discussion for another day). Also, visit Chuck Close’s Wikipedia page. Dude’s inspirational.
Erik Kaestner is a second-year Ph.D. student in the Multi-Modal Imaging Laboratory with Eric Halgren. When he’s not dabbling in virtual reality and Parkinson’s EEG experiments, he studies the neural representation of language using intracortical electrophysiological techniques.
References
1) Chittka, L., & Dyer, A. (2012). Cognition: Your face looks familiar. Nature,481(7380), 154-155.
2) http://en.wikipedia.org/wiki/Chuck_close
3) Johnson, M. H. (2005). Subcortical face processing. Nature Reviews Neuroscience, 6(10), 766-774.
4) Pessoa, L., & Adolphs, R. (2010). Emotion processing and the amygdala: from a ‘low road’ to ‘many roads’ of evaluating biological significance. Nature Reviews Neuroscience, 11(11), 773-783.
5) Farah, M. J., Rabinowitz, C., Quinn, G. E., & Liu, G. T. (2000). Early commitment of neural substrates for face recognition. Cognitive Neuropsychology, 17(1-3), 117-123.
6) Tarr, M. J., & Gauthier, I. (2000). FFA: a flexible fusiform area for subordinate-level visual processing automatized by expertise. Nature neuroscience, 3, 764-770
7) Sugita, Y. (2008). Face perception in monkeys reared with no exposure to faces. Proceedings of the National Academy of Sciences, 105(1), 394-398.
8) Meyer-Lindenberg, A., Domes, G., Kirsch, P., & Heinrichs, M. (2011). Oxytocin and vasopressin in the human brain: social neuropeptides for translational medicine. Nature Reviews Neuroscience, 12(9), 524-538.
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