Macaque monkeys demonstrate how our brains sort through the faces we see
How long does it take you to identify a person’s face? If you’ve gotten a good view of someone, you’re probably not even aware of the work your brain is doing to recognize the shapes in front of you as a person’s face. Even if the process of piecing together the exact curve of a cheekbone, the texture of a forehead and the cleft of a chin can happen without you noticing, it’s only possible thanks to the specialized brain structures handling the task. Researchers have been honing in on the exact formula brains use to make sense of all these features, finding that as few as 50 attributes can be sufficient to help you spot your neighbor in a crowded room in the blink of an eye.
Putting the pieces together
Researchers have known for some time about a section of the brain called the fusiform face area, but to see it in action they watched the brains of macaque monkeys who were looking at photos. Fortunately, the specialized neurons that recognize faces evolved in a shared ancestor don’t get too picky about the species of the viewed face, and the monkeys’ brains responded to pictures of humans in the same way they would look at closer kin. As the monkeys looked at the pictures, the activity of just 205 neurons was closely monitored to see which specific sites were needed to parse a face. That recorded data was parsed into 50 types of visual data, such as face shape, distance between the eyes, or skin texture. To build a face in the brain, each of these attributes were basically analyzed by different neurons in parallel, then assembled into the rational image we consciously recognize.
Observing all this activity in the macaque monkey brains was important, but to see if that activity was functioning the way researchers hypothesized, a test was needed. The process was then reversed to see if it would created the expected result— in this case, a face that looked like the face seen in the photos. Activity from the monitored neurons was translated back into visual information, then assembled digitally. The faces synthesized from the monkey’s brain cells weren’t perfect clones, but they were close enough that you’d recognize the person in the image.
Special functions just for faces?
As visual, social animals, it’s not a shock that our brains, and those of the macaques, carry such a fine-tuned toolkit for spotting faces. If anything, the system may be too sensitive, forcing us to think of a face every time we see two dots above a line. For researchers, the next question is to see just how specialized this facial recognition is. When looking at objects that aren’t quite as exciting as a potential friend, mate or rival, do our brains sort things in the same way? Or does our brain recognize chairs or trees in a different way, putting facial recognition in its own category of perception?
Source: Photos of human faces reassembled from monkeys’ brain signals by Andy Coghlan, New Scientist