By Ashleigh J. Willis Published 15th Jan 2022
The global response to the COVID-19 pandemic has initiated an enormous shift in our social landscape. With the introduction of mask-wearing to public indoor spaces, unprecedented in modern times and possibly proving as the largest social visual perception experiment ever conducted, it has of course become routine for us to miss out on a central component of human social interaction: others’ faces. The partial occlusion of the face — and thereby the social information provided by changes in people’s facial expressions — by masks presents a new challenge to our social visual processing system. How are we meant to read the social and emotional cues of others when a large portion of the information is missing? Do we adequately adapt to this perturbation of the social world? And, importantly, what are the consequences of such a disruption during critical periods of child development?
Facial Processing and Environmental Changes
Like all neural processes, facial recognition, emotional, and social cognition are all extraordinarily sophisticated feats of the natural world. For the functioning of these complex operations, our brains recruit a network of regions and cellular subtypes which together orchestrate facial processing. And, while the molecular mechanisms underpinning these processes still aren’t fully understood, we do have a reasonable grasp on the brain regions involved.
In adults, there are two primary systems implicated in face processing. Sometimes referred to as the ‘core’ and ‘extended’ systems, the core system, in brief, depends upon a region called the occipital face area and is responsible for the initial processing and differentiation of broad facial features, such as the eyes and mouth. Following core processing, information is directed toward the ‘extended’ system, in which is situated a specialized cortical region called the fusiform face area. As may be inferred from the name, the fusiform face area is tasked with the perception of human faces and potentially emotion processing. Additional brain areas are also tasked with the tracking of another person’s dynamic facial features and movements, with the culminating data from these systems, as well as the further refinement provided by numerous higher-order regions of the brain, ultimately informing the brain’s identification of social and emotional cues.
This complex system continues to develop well into adolescence and, potentially, beyond. It is important to note, however, that these regions are not static and can be influenced by environmental disruption. Persistent stress, for example, has been shown to alter the number and strength of the synaptic connections integral to the transmission of information between neurons in these areas. Thus, the insight that our face processing systems are somewhat malleable is important when considering our adaptation to extensive mask-wearing.
Masks and the Mature Brain
With a practical but certainly not extensive tour of the brain’s neural face processing network under our belts, what does the current research tell us about the impacts of ‘masking up’ on the adult brain?
Well, as you might already expect, the practise of wearing masks is not without consequence. Research conducted by clinical psychologists Daniel Carragher and Peter Hancock of the University of Stirling, for instance, has suggested that our ability to identify faces, both familiar and unfamiliar, is greatly impaired when face masks are worn. In line with this, a study published in Scientific Reports by Erez Freud and colleagues reported a significant decrease in the performance of participants engaged in a facial recognition memory task (the Cambridge Face Memory Test) when viewing masked faces as opposed to unmasked faces.
Additional work suggests that the perception of a masked face drastically alters the type of information that we account for when making vital judgements on emotional facial expressions. This effect was further explored by a 2021 study which found that participants relied more heavily on facial landmarks (referred to as ‘visual’ cues) than emotion or arousal information (‘affective’ cues) when viewing masked faces. In addition, emotion perception was also measured before and after the widespread mask adoption in the same cohort of participants. The data revealed an overall increase in visual cue use in September 2020 as compared to April 2020, and, significantly, the largest shift from affective to visual cues was recorded in participants who had higher incidences of social interaction.
The study appears to reveal an overall shift in the way adults process social and emotional facial information, with this change increasing with elevated exposure to masked faces. Incidentally, an aforementioned study from Freud and colleagues also revealed disruption to normal hallmarks of facial recognition when masks were present. Thus, it is arguable that the shift away from facial emotion cues may produce some critical effects on social function, an effect that is clear when looking at, for example, a recent German study which reported that face masks diminish the ability of the observer to categorise emotion, with perceptions of trustworthiness, likability, and closeness also being reduced.
We can see in the large majority of current research that mask-wearing does alter face perception and that this may have an effect on emotion processing and social interaction. In the post-pandemic era, should widespread mask-wearing ever cease, it will be important to understand the long-term impact of these changes. As of yet, however, we have no such information on the biological mechanisms which underpin these changes and considering the remarkable plasticity of the brain, it is conceivable that consistent viewing of partially occluded faces could initiate changes in synaptic strength, altering information flow throughout the network or producing novel connections. This speculation, though, is yet to be evaluated, and whether robust negative or sustained effects are caused as a consequence of persistent viewing of masked faces remains to be seen.
Masks and the Developing Brain
Throughout the pandemic, opposition to the perceived effects of mask-wearing has often been most fierce when concerned with one group of people — children. Children of course have had their lives chronically interrupted since the beginning of the pandemic, with crucial early learning stages being severely disrupted by long periods of school closures and restrictions on many social activities. To this end, it is conceivable that masks will continue to be pervasive in the lives of our children and, in many places around the world, children of certain ages for large portions of the day are now only able to view the partially covered faces of both adults and their peers due to extensive government mandates.
Understandably, many parents have begun to ask what the impact of this could be on the development of their children. We can gather some insight into these issues from studies conducted before the COVID-19 pandemic. In a 2012 study, Debi Roberson of the University of Essex and colleagues investigated facial expression processing in children aged three to nine years old and the ability for these children to correctly recognise emotional expressions in photographs of adult faces. These faces were either bare, occluded by sunglasses, or covered by a surgical mask.
In a promising result that caught the attention of the pro-mask lobby and mainstream news outlets in November 2021, children under the age of nine intriguingly presented no clear impairments when classifying the expressions of faces covered with masks or sunglasses. The mainstream media, however, predictably using this discovery to assert that “masks are probably at the bottom of the list of things to be concerned about,” missed one very pertinent finding: facial expression recognition in older children was significantly impaired by mask facial occlusion. In fact, when assessing masked faces, children aged nine and ten are markedly less accurate in their classifications compared to their younger peers, with the adult cohort included in the study also performing worse than seven and eight-year-olds.
The authors of Roberson et al.’s study suggest this ‘drop off’ in performance is consistent with the emergence of more mature facial emotion and identity recognition strategies as we grow older. Allowing for the inclusion of contextual information in facial expression-related decisions, younger children tend to preferentially attend to the eye area when making decisions on the meanings of another’s facial expressions, even when the full face is visible. Hence, partial occlusion by a mask makes little difference in their facial processing strategies. As we mature, however, our emotional understanding and associated facial processing strategies become more sophisticated, with a holistic view of the face and contextual information becoming more important. As such, the reduction in facial information available from a masked face becomes a problem with maturation.
More recent studies have also addressed this issue. In 2020, Ashley Ruba and Seth Pollak in a study similar to that of Roberson’s presented data which showed that children can still recognise emotions to some degree. In its findings, however, the study did suggest that the occlusion of the face by a mask or shade does have a significant impact on the frequency of a child’s accuracy when identifying emotions. The issue is, children have not historically encountered tinted lens adorned faces throughout the majority of public life: teachers, of course, do not wear sunglasses indoors, doctors don't often sport Ray-Ban decorated eyes, and supermarkets don’t resemble an airport Sunglasses Hut. For many workers in these areas, though, masks are now mandated in these situations; a fact which could produce severe results for our children.
Still, it is important to note a recent letter which contradicts the aforementioned studies. Published in JAMA Psychiatry, the authors reported that there are only marginal reductions in the ability for children to accurately classify emotional expressions in masked faces when using a smartphone-based task. Speaking to the American Association for the Advancement of Science in EurekAlert, Ashley Ruba, the researcher who conducted the study, correctly points out the resilience of children:
“Kids are really resilient. They're able to adjust to the information they're given, and it doesn't look like wearing masks will slow down their development in this case.”
Other scientists have speculated on this issue of adaptability and recovery from the implementation of mask wearing. Dr Hugh Bases, clinical associate professor of paediatrics at Hassenfeld Children's Hospital at NYU Langone Health, for instance, told CNN:
“I think once masks are gone or almost gone, whatever impact it has, we'll quickly recover.”
Arguably such speculation, though founded in research regarding the remarkable plasticity and adaptability of the developing brain, seems premature and, as with many issues surrounding the pandemic, we have a limited amount of data available to make more definitive conclusions. Indeed, experiments that involve participants looking at and classifying photographs are somewhat limited: how much is generalisable from interactions with photographs to real-world scenarios, for instance? Truthfully, we don’t have the data or a comparable historical example to make those sorts of speculations; we have indeed rarely been in a situation wherein children have been so consistently met by masked faces.
Conclusively, though, what we do know is that sensory experience can affect brain development. Moreover, we know that environmental disruption — including social and emotional neglect and stressors — can interact with the developmental trajectory of the brain. Significant environmental disruption in early years has been linked with a number of adverse outcomes, including an increased prevalence of psychiatric disorders in later life. It is critical to note that the response to these environmental perturbations appears to be linked to our genetics (so-called gene-environment interactions). Thus, it is probable that the consequences of disruption to the sensory environment will vary between individuals.
Of course, emotional and social information is conveyed by more than facial expressions. We know that vocal tonality and body gestures play a substantial role too. Nonetheless, it is demonstrable that evolution has seemingly set aside a brain region — the fusiform face area — specifically tasked with the recognition of human faces and, while this area is certainly not the sole contributor of social and emotional facial processing, it is remarkably specific. Biological systems are generally thrifty with resources, so the division of a region of the cortex solely for facial recognition highlights the importance of this process. With this in mind, it is reasonable to say that facial expressions are likely a key driver in our social and emotional cognition.
The data we currently have suggests that government advice or the requirement to wear masks in public spaces is not ineffectual for adults or children. And, while our current data lacks depth, it indicates that consideration should be given to the social implications of long-term mask adoption in our COVID-19 recovery plans. While it is unclear how the data will fall regarding the long-term consequences of population-wide masking, and it will no doubt be many years before we can fully assess the consequences, it is nonetheless advisable that we exercise caution in our assumptions about the impact of such a huge disruption in our abilities for social perception.
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