Studies of social cognition examine how organisms process and act on the presence, intentions, actions, and behavioural outcomes of others in social contexts. Many real-life social interactions unfold during direct face-to-face contact and rely on immediate, time-continuous feedback about mutual behaviour and changes in the shared environment. Yet, essential aspects of these naturalistic conditions are often lacking in experimental laboratory settings for direct dyadic interactions, i.e., interactions between two people. Here, we describe a novel experimental setting, the Dyadic Interaction Platform (DIP), designed to investigate the behavioural and neural mechanisms of real-time social interactions. Based on a transparent, touch-sensitive, bi-directional visual display, this design allows two participants to observe visual stimuli and each other simultaneously, allowing face-to-face interaction in a shared vertical workspace. Different implementations of the DIP facilitate interactions between two human adults, adults and children, two children, nonhuman primates and in mixed nonhuman-human dyads. The platforms allow for diverse manipulations of interactive contexts and synchronized recordings of both participants’ behavioural, physiological, and neural measures. This approach enables us to integrate economic game theory with time-continuous sensorimotor and perceptual decision-making, social signalling and learning, in an intuitive and socially salient setting that affords precise control over stimuli, task timing, and behavioural responses. We demonstrate the applications and advantages of DIPs in several classes of transparent interactions, ranging from value-based strategic coordination games and dyadic foraging to social cue integration, information seeking, and social learning.
Facial width-to-height ratio (fWHR) is an extensively studied morphological measure, which was presumably shaped by sexual selection and has been linked to a wide range of perceptual and physiological traits. Underpinning these associations is the premise that fWHR is larger in men, which empirically exhibits a mixed and equivocal pattern in the literature due to variation in measurement, large sample sizes revealing small but significant differences, and a lack of control of body size. In Study 1, in a sample of 1949 faces, we used a Bayesian hierarchical model that incorporates prior information to simultaneously estimate sexual dimorphism in fWHR, adjusted for body size, across five measurement types. While we found larger fWHR in women, comparing this effect to variability in fWHR due to image capture settings revealed no robust evidence of sex differences in fWHR. In Study 2, we investigated sex differences in facial width specifically (also adjusted for body size), again incorporating prior information, and confirmed men have greater face width than women. Advances in this area can be made by shifting focus away from arbitrary ratios like fWHR to direct measures like facial width – as well as carefully considering prior evidence of existing associations.
