Do I know you?

May 25, 2021

Written by: Catrina Hacker

The fastest and easiest way to recognize another human is by their face. One of the most remarkable features of human face recognition is that we only need to see a person once or twice before we can recognize them in various future encounters across different contexts and conditions. Although we might sometimes struggle to match a name to a face, most people are able to quickly and effortlessly recognize the faces of people they have previously encountered. Despite this seeming ease of recognition, there is a wide range of face recognition ability. Some people have a condition called prosopagnosia. People with prosopagnosia can see faces just as well as other people, but they cannot recognize them. Even after several encounters with an individual, they struggle to recognize familiar faces, including close friends and family. On the other end of the spectrum, super recognizers recognize nearly every face they have ever seen. These people would not only recognize the main character of a film they watched, but might also recognize an extra who appeared in the background of a single scene, or a person they saw once at the gas station. By studying people who are most and least skilled at recognizing faces, cognitive neuroscientists have learned a lot about the neural mechanisms that support face recognition. 

Developmental and Acquired Prosopagnosia

There are two types of prosopagnosia: acquired and developmental. People with acquired prosopagnosia are born with the ability to recognize faces, but lose this ability after a brain injury (e.g., following car accident, stroke, etc.). This type of prosopagnosia is rare, as a very specific kind of injury must occur to produce these symptoms. Conversely, people with developmental prosopagnosia are born without the ability to recognize faces. These individuals have not experienced any kind of brain damage, but still struggle to recognize faces. People with developmental prosopagnosia make up approximately 2% of the population and have a wide spectrum of ability. Some can learn to recognize close family and friends after many encounters, while others cannot recognize a face no matter how many times they have seen it. No matter the type of prosopagnosia, the effects can be devastating1. Individuals with prosopagnosia report higher levels of anxiety and depression than their neurotypical peers. Many people with prosopagnosia also report isolating themselves from social interactions for fear of offending people they might not recognize. 

Super Recognizers

Unlike people with prosopagnosia, super recognizers are exceptionally good at recognizing faces2. These people score very high on face recognition tests, even when the images are low quality or partially covered. One test of super recognizers is their ability to identify celebrities from their baby pictures. You can test your own abilities with this test developed by researchers at Dartmouth College and Harvard University that determines how well you can distinguish faces of celebrities from those of a doppelganger who looks very similar. The existence of super recognizers has only recently been documented, but there is already a lot of interest in how we might be able to use these abilities to help society. A 2016 New Yorker article documented the success of super recognizers in the London Metropolitan Police Service, who could identify suspects after seeing a single grainy image from CCTV footage3. While there is still much more research to be done on super recognition and its reliability before these abilities should be broadly applied4, we can study these exceptionally good face recognizers to learn valuable things about how the brain accomplishes face recognition. 

Neural Mechanisms of Face Recognition

Face recognition is mediated by a network of brain regions that are specialized for processing faces5. Two of the most well-established regions involved in this process are the Fusiform Face Area (FFA) and Occipital Face Area (OFA). FFA and OFA can be located in human subjects using fMRI. Subjects are shown many images of face and non-face objects (such as houses). FFA and OFA were originally identified by finding the regions that respond more strongly to pictures of faces than to other objects, and consistently occur at the same anatomical location across subjects. While these experiments can identify regions that respond more strongly to faces than to other kinds of stimuli, they can’t tell us about the necessity of these regions for face recognition. One important indication that these regions are necessary for face recognition, though, is that people with acquired prosopagnosia have damage to FFA and/or OFA. By studying people with acquired prosopagnosia with injuries to only FFA or OFA, we also know that both regions are necessary and that injury to just one can severely impair face recognition abilities6

People with developmental prosopagnosia and super recognizers have also been used to study the importance of the size and connections between these face-selective brain regions. Several studies show that people with developmental prosopagnosia have weaker connections between the regions in this face network than neurotypical subjects, which could explain the difficulty that they have recognizing faces. People with developmental prosopagnosia also tend to have smaller FFAs than neurotypical peers7. While super recognizers have been studied less, they tend to show stronger activation of FFA than people with prosopagnosia and have larger FFAs8. In another study, a group of neuroscientists stimulated FFA in an awake patient who was implanted with electrodes to monitor their epilepsy. When the scientists stimulated FFA, the patient reported a face-specific effect that caused the faces of people in the room to be “metamorphosed”9. By artificially impairing face recognition, this study supports a very specific role of FFA in face recognition. 

By relating differences in face recognition ability to differences in neural activity, neuroscientists have learned a lot about the importance of these regions in face recognition. This has important implications not only for our general understanding of neural mechanisms of face recognition, but also for identifying methods to help people with prosopagnosia regain this essential social function. 

References

1. Yardley, L., McDermott, L., Pisarski, S., Duchaine, B. & Nakayama, K. Psychosocial consequences of developmental prosopagnosia: A problem of recognition. J. Psychosom. Res. 65, 445–451 (2008).

2. Russell, R., Duchaine, B. & Nakayama, K. Super-recognizers: People with extraordinary face recognition ability. Psychon. Bull. Rev. 16, 252–257 (2009).

3. Keefe, P. R. The Detectives Who Never Forget a Face. 13 (2016).

4. Ramon, M., Bobak, A. K. & White, D. Super‐recognizers: From the lab to the world and back again. Br. J. Psychol.110, 461–479 (2019).

5. Grill-Spector, K., Weiner, K. S., Kay, K. & Gomez, J. The Functional Neuroanatomy of Human Face Perception. Annu. Rev. Vis. Sci. 3, 167–196 (2017).

6. Rossion, B. Constraining the cortical face network by neuroimaging studies of acquired prosopagnosia. NeuroImage 40, 423–426 (2008).

7. Zhang, J., Liu, J. & Xu, Y. Neural Decoding Reveals Impaired Face Configural Processing in the Right Fusiform Face Area of Individuals with Developmental Prosopagnosia. J. Neurosci. 35, 1539–1548 (2015).

8. Russell, R. Yue, X. Nakayama, K. Tootell, R. B.H. (2010). Neural differences between developmental prosopagnosics and super-recognizers [Abstract]. Journal of Vision, 10(7):582, 582a, http://www.journalofvision.org/content/10/7/582

9. Parvizi, J. et al. Electrical Stimulation of Human Fusiform Face-Selective Regions Distorts Face Perception. J. Neurosci.32, 14915–14920 (2012).

Cover Image from Pixabay

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