Chunking by social relationship in working memory

Evidence for a role of synchrony but not common fate in the perception of biological group movements

Extensive research has shown that observers are able to efficiently extract summary information from groups of people. However, little is known about the cues that determine whether multiple people are represented as a social group or as independent individuals. Initial research on this topic has primarily focused on the role of static cues. Here, we instead investigate the role of dynamic cues. In two experiments with male and female human participants, we use EEG frequency tagging to investigate the influence of two fundamental Gestalt principles - synchrony and common fate - on the grouping of biological movements. In Experiment 1, we find that brain responses coupled to four point-light figures walking together are enhanced when they move in sync vs. out of sync, but only when they are presented upright. In contrast, we found no effect of movement direction (i.e., common fate). In Experiment 2, we rule out that synchrony takes precedence over common fate by replicating the null effect of movement direction while keeping synchrony constant. These results suggest that synchrony plays an important role in the processing of biological group movements. In contrast, the role of common fate is less clear and will require further research.

Visual Preference for Socially Relevant Spatial Relations in Humans and Monkeys

As a powerful social signal, a body, face, or gaze facing toward oneself holds an individual's attention. We asked whether, going beyond an egocentric stance, facingness between others has a similar effect and why. In a preferential-looking time paradigm, human adults showed spontaneous preference to look at two bodies facing toward (vs. away from) each other (Experiment 1a, N = 24). Moreover, facing dyads were rated higher on social semantic dimensions, showing that facingness adds social value to stimuli (Experiment 1b, N = 138). The same visual preference was found in juvenile macaque monkeys (Experiment 2, N = 21). Finally, on the human development timescale, this preference emerged by 5 years, although young infants by 7 months of age already discriminate visual scenes on the basis of body positioning (Experiment 3, N = 120). We discuss how the preference for facing dyads-shared by human adults, young children, and macaques-can signal a new milestone in social cognition development, supporting processing and learning from third-party social interactions.

Innate sensitivity to face-to-face biological motion

Sensitivity to face-to-face stimuli configurations, which likely indicates interaction, seems to appear early in infants' development, and recently a preference for face-to-face (vs. other spatial configurations) has been shown to occur in macaque monkeys. It is unknown, however, whether such a preference is acquired through experience or as an evolutionary-given biological predisposition. Here, we exploited a precocial social animal, the domestic chick, as a model system to address this question. Visually naive chicks were tested for their spontaneous preferences for face-to-face vs. back-to-back hen dyads of point-light displays depicting biological motion. We found that female chicks have a spontaneous preference for the facing interactive configuration. Males showed no preference, as expected due to the well-known low social motivation of males in this highly polygynous species. These findings support the idea of an innate and sex-dependent predisposition toward social and interacting stimuli in a vertebrate brain such as that of chicks.

Electrophysiological hallmarks for event relations and event roles in working memory

The ability to maintain events (i.e., interactions between/among objects) in working memory is crucial for our everyday cognition, yet the format of this representation is poorly understood. The current ERP study was designed to answer two questions: How is maintaining events (e.g., the tiger hit the lion) neurally different from maintaining item coordinations (e.g., the tiger and the lion)? That is, how is the event relation (present in events but not coordinations) represented? And how is the agent, or initiator of the event encoded differently from the patient, or receiver of the event during maintenance? We used a novel picture-sentence match-across-delay approach in which the working memory representation was "pinged" during the delay, replicated across two ERP experiments with Chinese and English materials. We found that maintenance of events elicited a long-lasting late sustained difference in posterior-occipital electrodes relative to non-events. This effect resembled the negative slow wave reported in previous studies of working memory, suggesting that the maintenance of events in working memory may impose a higher cost compared to coordinations. Although we did not observe significant ERP differences associated with pinging the agent vs. the patient during the delay, we did find that the ping appeared to dampen the ongoing sustained difference, suggesting a shift from sustained activity to activity silent mechanisms. These results suggest a new method by which ERPs can be used to elucidate the format of neural representation for events in working memory.

Converging evidence that left extrastriate body area supports visual sensitivity to social interactions

Navigating our complex social world requires processing the interactions we observe. Recent psychophysical and neuroimaging studies provide parallel evidence that the human visual system may be attuned to efficiently perceive dyadic interactions. This work implies, but has not yet demonstrated, that activity in body-selective cortical regions causally supports efficient visual perception of interactions. We adopt a multi-method approach to close this important gap. First, using a large fMRI dataset (n = 92), we found that the left hemisphere extrastriate body area (EBA) responds more to face-to-face than non-facing dyads. Second, we replicated a behavioral marker of visual sensitivity to interactions: categorization of facing dyads is more impaired by inversion than non-facing dyads. Third, in a pre-registered experiment, we used fMRI-guided transcranial magnetic stimulation to show that online stimulation of the left EBA, but not a nearby control region, abolishes this selective inversion effect. Activity in left EBA, thus, causally supports the efficient perception of social interactions.

Seeing social interactions

Seeing the interactions between other people is a critical part of our everyday visual experience, but recognizing the social interactions of others is often considered outside the scope of vision and grouped with higher-level social cognition like theory of mind. Recent work, however, has revealed that recognition of social interactions is efficient and automatic, is well modeled by bottom-up computational algorithms, and occurs in visually-selective regions of the brain. We review recent evidence from these three methodologies (behavioral, computational, and neural) that converge to suggest the core of social interaction perception is visual. We propose a computational framework for how this process is carried out in the brain and offer directions for future interdisciplinary investigations of social perception.

Intermodulation responses show integration of interacting bodies in a new whole

People are often seen among other people, relating to and interacting with one another. Recent studies suggest that socially relevant spatial relations between bodies, such as the face-to-face positioning, or facingness, change the visual representation of those bodies, relative to when the same items appear unrelated (e.g., back-to-back) or in isolation. The current study addresses the hypothesis that face-to-face bodies give rise to a new whole, an integrated representation of individual bodies in a new perceptual unit. Using frequency-tagging EEG, we targeted, as a measure of integration, an EEG correlate of the non-linear combination of the neural responses to each of two individual bodies presented either face-to-face as if interacting, or back-to-back. During EEG recording, participants (N = 32) viewed two bodies, either face-to-face or back-to-back, flickering at two different frequencies (F1 and F2), yielding two distinctive responses in the EEG signal. Spectral analysis examined the responses at the intermodulation frequencies (nF1±mF2), signaling integration of individual responses. An anterior intermodulation response was observed for face-to-face bodies, but not for back-to-back bodies, nor for face-to-face chairs and machines. These results show that interacting bodies are integrated into a representation that is more than the sum of its parts. This effect, specific to body dyads, may mark an early step in the transformation towards an integrated representation of a social event, from the visual representation of individual participants in that event.

Behavioral and neural markers of visual configural processing in social scene perception

Research on face perception has revealed highly specialized visual mechanisms such as configural processing, and provided markers of interindividual differences -including disease risks and alterations- in visuo-perceptual abilities that traffic in social cognition. Is face perception unique in degree or kind of mechanisms, and in its relevance for social cognition? Combining functional MRI and behavioral methods, we address the processing of an uncharted class of socially relevant stimuli: minimal social scenes involving configurations of two bodies spatially close and face-to-face as if interacting (hereafter, facing dyads). We report category-specific activity for facing (vs. non-facing) dyads in visual cortex. That activity shows face-like signatures of configural processing -i.e., stronger response to facing (vs. non-facing) dyads, and greater susceptibility to stimulus inversion for facing (vs. non-facing) dyads-, and is predicted by performance-based measures of configural processing in visual perception of body dyads. Moreover, we observe that the individual performance in body-dyad perception is reliable, stable-over-time and correlated with the individual social sensitivity, coarsely captured by the Autism-Spectrum Quotient. Further analyses clarify the relationship between single-body and body-dyad perception. We propose that facing dyads are processed through highly specialized mechanisms -and brain areas-, analogously to other biologically and socially relevant stimuli such as faces. Like face perception, facing-dyad perception can reveal basic (visual) processes that lay the foundations for understanding others, their relationships and interactions.