Making Social Signals Visible
Body posture, movement, and expression are important components of social communication for humans and other primates. They help individuals recognize the intentions, moods, or reactions of others. To better understand how the brain processes such signals, researchers need images and movements that can be controlled with great precision. Digital avatars make exactly this possible: They resemble real animals, but can be systematically modified, for example in terms of movement, viewing angle, or appearance.
A New Method Without Body Markers
The team led by Prof. Dr. Martin Giese, research group leader at the Hertie Institute for Clinical Brain Research, together with first author Lucas Martini, developed “MacAction,” a method for creating realistic, animated macaque avatars. One particular challenge was that standard techniques used in the film industry usually rely on markers attached to the body. In macaques, this is hardly feasible, because the animals would destroy the markers and their natural behavior would be affected. The researchers therefore used multiple cameras and a markerless method that records natural movements and transfers them into precise 3D animations.
“Our goal was to generate realistic social stimuli without influencing the animals’ behavior through technical aids attached to their bodies,” says Lucas Martini of the Hertie Institute for Clinical Brain Research.
When Almost Real Is Not Real Enough
In an eye-tracking experiment with rhesus macaques, the researchers investigated how the animals responded to avatars with varying degrees of realism. The experiment revealed an “uncanny valley effect”: Very realistic or clearly artificial representations were perceived as more pleasant than intermediate versions that looked almost real, but not quite. A comparable phenomenon is also known in humans, for example in responses to robots, video game characters, or virtual humans. The study suggests that humans and macaques share important basic principles of social perception.
“What was crucial was that the animals showed similar gaze behavior in response to the highly realistic animations as they did to real videos. This shows that such avatars are suitable for controlled experiments on social perception,” says Prof. Rufin Vogels of the Leuven Brain Institute in Belgium.
Benefits for Research and Society
The findings of this basic research have important scientific and societal relevance and provide a foundation for future translational research. First, computer-generated artificial agents are playing an increasingly important role in our everyday lives, and it is an important question whether such stimuli are perceived similarly by other species and whether their processing is based on similar principles. Second, the visual processing of social signals and social communication is altered in several relatively common clinical disorders, such as autism spectrum disorders, schizophrenia, and dementia.
“The precisely controllable avatars we developed are essential for investigating and understanding the underlying neural mechanisms. This is the basis for developing targeted clinical approaches for the diagnosis and treatment of disorders of social perception,” Prof. Giese summarizes.
Publication: Realistic monkey body animation reveals an uncanny valley in macaque body perception.
DOI: https://doi.org/10.1371/journal.pbio.3003880
Experts
Prof. Dr. Martin Giese
Research Group Leader
Hertie Institute for Clinical Brain Research
Prof. Dr. Rufin Vogels
Research Group Leader
Leuven Brain Institute
Copyright: Martin Giese
