Periodic Reporting for period 3 - FACEDIFF (Individual differences in facial expressivity: Social function, facial anatomy and evolutionary origins)
Période du rapport: 2022-01-01 au 2023-06-30
Communicating with others via the face is crucial for navigating our social world. Deficits in facial expression production can have a significant bearing on social interaction, characterising several clinical conditions such as autism spectrum disorder, schizophrenia and Parkinson’s disease. Despite this, we know surprisingly little about individual differences in facial expressivity in the typical population, what causes these differences and whether such differences have an impact on individual lives. In part, this could be due to an historical focus on the universal nature of facial expression, assuming that individual differences are random ‘noise’, rather than an evolutionarily relevant characteristic. The FACEDIFF project diverges from this classic approach and is testing the hypothesis that individual differences in facial expressivity are meaningful and reflect different strategies in engaging with others in social interaction. A better understanding of these individual differences will help us appreciate the full range of human communicative behaviour. We predict that individuals are equipped differentially to engage with their social environment: expressivity has a benefit (to engage closely with others) but also a cost (exposing your social actions could risk being cheated by others). We also predict that individual expressivity is related to the size and quality of an individual’s social network, reflecting how easily they interact and build relationships with others. FACEDIFF combines psychological, anatomical and cross-species methods to provide the first thorough interdisciplinary investigation of individual differences in facial expressivity. First, individual variation in production and perception of facial expressions are being measured via online and laboratory behavioural experiments. Second, variation in human facial musculature is documented through cadaveric dissection and existing MRI databases. Third, facial expressivity is examined in a closely related non-human primate model (rhesus macaques) to determine whether patterns are unique to humans. This project will be the first to provide a comprehensive and interdisciplinary perspective on individual differences in facial expression and will stimulate new theories on the function and evolution of facial communication.
The FACEDIFF team is comprised of 15 staff working over the three sections of the project. At this mid-stage of the project, the human behaviour team have produced three outputs, the first two using existing data while Covid-19 prevented the collection of new data. Existing data from an ESRC funded project has been analysed showing that older adults with more agreeable and extroverted personality styles have larger social networks (Rollings et al., 2022). Existing data from a funded British Academy grant has been examined showing people who are more expressive when they are stressed are more likeable (Whitehouse et al., 2022). We have also completed an extensive pilot study prior to the main larger scale studies. We recorded naturalistic social interactions via video call between 52 participants and a confederate, and then asked 176 independent raters to make judgements about the participants in the call. More expressive and agreeable people were rated as more likeable, and were better negotiators during a conflict social interaction. We are now aiming to replicate this effect with a large, multimodal corpus of 1,656 recorded conversations. The anatomy team have conducted facial dissections on two human cadaveric specimens. Around 15-20 additional new specimens have been identified for use within the project, along with 44 head and neck specimens housed for teaching purposes. Thirty-four macaque specimens have been identified and secured for dissection. The team also built a digital dissection and computer model using the MRI data of the face. The primate behaviour team have completed data collection with wild macaques and built a video library of ~1950 videos (from ~105 individuals) for facial behaviour analysis. The team have also collected data with captive macaques which is approximately 75% complete. This includes social network data and close-up video footage on ~75 individuals of 9 social groups, totalling ~50 hours of video footage and ~200 hours of focal data, plus data on mother-infant interactions. Cognitive experiments have also been conducted with the captive macaques, testing 90 individuals on their facial expression processing expertise. Finally, the whole FACEDIFF team have worked on two review papers: an analysis of Charles Darwin’s original comparisons between human facial expressions and those of primates, and an opinion paper arguing that the face is central to all primate communication.
The findings of the FACEDIFF project have the potential to change our understanding of facial expression in social interaction. Our initial data collection on human behaviour (The face in everyday social interaction: social outcomes and personality correlates of facial behaviour) is in my view the most significant achievement of FACEDIFF so far. This initial video call study has resulted in a rich dataset and provided valuable findings. Specifically, we have shown that how people use their faces during real-life social interactions is radically different to the picture painted by mainstream scientific discourse. The ‘universal expressions of emotion’ are almost entirely absent, with the exception of smiling, and yet facial movements are occurring frequently during the whole conversation. Social outcomes (conflict resolution, friendship formation) are strongly associated with these movements. This was unexpected (to an extent) and has the potential to advance the field by shifting focus from supposed prototypical configurations to more fluid and dynamic movements produced during social interaction. This work is complimented by the anatomy strand which we believe will show greater variation in facial muscles than previously understood. The development of our non-human primate database has also been fruitful, and we are currently processing approximately 350 hours of close-up facial footage of both captive and wild rhesus macaques. We believe this database of videos is among the largest of its kind and expect it to be a very valuable resource to achieve the objectives of FACEDIFF and beyond. The richness of this database has already prompted the development of subprojects in line with the main objectives, including a smaller project assessing the impact of male expressivity on group dynamics and social structure. Our projected findings are similar to those with humans, we expect individuals with greater expressivity to find it easier to build social relationships with others. In sum, through interdisciplinary analysis of real-world, every day behaviour we expect to build a new evolutionary perspective on the adaptive function of individual facial expressivity styles in humans and other primates.