Facial signals are crucial in the social interactions of mammals, as they provide a means to modify the behavior of others by conveying information about both internal states and/or external conditions. Since Charles Darwin's seminal publication on the Expression of the Emotions in Man and Animals, there have been many theoretical and methodological advancements in the way that we study the physical form and social function of facial signals. This includes the development of rigorous manual coding approaches, such as Facial Action Coding Systems, as well as the use of automated methods like Facial Landmark Detection Systems. As these systems become increasingly used in mammal communication research, questions arise about their socio-ecological context, ethical use, and interpretability. This special issue invites contributions that explore the form and function of mammal facial signals, including those of humans, particularly given the emergence of new automated systems that enhance and challenge traditional observational approaches.

1. What is the relationship between the physical form and social function of mammal facial signals?
2. How do socio-ecological factors influence the form and function of these signals?
3. How can we utilize (and enhance) manual coding techniques to study facial signals in mammals?
4. How can we utilize (and enhanced) automated coding techniques to study facial signals in mammals?
5. How do manual coding techniques compare to automated methods in the study of mammalian facial signals?
6. Is there variation in facial signaling behavior among mammals, individuals, social groups, and populations? If so, to what extent and why?
7. What can we learn about the evolution of mammalian facial signals by making between-species comparisons?
8. What is the role and significance of facial signaling during multimodal communication?

This research topic invites contributions that use both manual and/or automated methods to examine mammalian facial signaling (including humans). We are particularly interested in comparative studies, interdisciplinary research, and those that utilize various coding and statistical techniques. Some example topics are presented below:

● Facial Action Coding Systems (FACS)
● Landmark Detection Systems
● Emotional Coding Scales (such as the Grimace Scale)
● Machine Learning (ML) & Artificial Intelligence (AI)
● Socio-Ecological and Socio-Communicative Complexity Hypotheses
● Complexity & Compositionality of Facial Signals
● Emotional View (EV) & Behavioral Ecology View (BECV) of Facial Signaling
● Core Affect Model and Emotional Appraisal Models
● Facial Feedback, Facial Mimicry & Facial Synchrony
● Multimodal Communication
● Facial Configuration and Recognition

We accept original research articles, reviews, methodological papers, and brief reports that offer critical insights or propose innovative frameworks. Submissions should clearly articulate how data-driven tools contribute to or challenge conventional understandings of mammalian facial signaling in social contexts.

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Innovative Insights into Mammalian Facial Signals