Previous research shows that the amygdala automatically responds to a face's trustworthiness when a face is clearly visible. However, it is unclear whether the amygdala could evaluate such high-level facial information without a face being consciously perceived. Using a backward masking paradigm, we demonstrate in two functional neuroimaging experiments that the human amygdala is sensitive to subliminal variation in facial trustworthiness. Regions in the amygdala tracked how untrustworthy a face appeared (i.e., negative-linear responses) as well as the overall strength of a face's trustworthiness signal (i.e., nonlinear responses), despite faces not being subjectively seen. This tracking was robust across blocked and event-related designs and both real and computer-generated faces. The findings demonstrate that the amygdala can be influenced by even high-level facial information before that information is consciously perceived, suggesting that the amygdala's processing of social cues in the absence of awareness may be more extensive than previously described.

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By many accounts cooperation appears to be a default strategy in social interaction

Humans form social coalitions in every society on earth, yet we know very little about how the general concepts us and them are represented in the brain. Evolutionary psychologists have argued that the human capacity for group affiliation is a byproduct of adaptations that evolved for tracking coalitions in general. These theories suggest that humans possess a common neural code for the concepts in-group and out-group, regardless of the category by which group boundaries are instantiated. The authors used multivoxel pattern analysis to identify the neural substrates of generalized group concept representations. They trained a classifier to encode how people represented the most basic instantiation of a specific social group (i.e., arbitrary teams created in the lab with no history of interaction or associated stereotypes) and tested how well the neural data decoded membership along an objectively orthogonal, real-world category (i.e., political parties). The dorsal anterior cingulate cortex/middle cingulate cortex and anterior insula were associated with representing groups across multiple social categories. Restricting the analyses to these regions in a separate sample of participants performing an explicit categorization task, the authors replicated cross-categorization classification in anterior insula. Classification accuracy across categories was driven predominantly by the correct categorization of in-group targets, consistent with theories indicating in-group preference is more central than out-group derogation to group perception and cognition. These findings highlight the extent to which social group concepts rely on domain-general circuitry associated with encoding stimuli's functional significance. (PsycINFO Database Record

We investigated how group membership impacts valence judgments of ingroup and outgroup members' emotional expressions. In Experiment 1, participants, randomized into 2 novel, competitive groups, rated the valence of in- and outgroup members' facial expressions (e.g., fearful, happy, neutral) using a circumplex affect grid. Across all emotions, participants judged ingroup members' expressions as more positive than outgroup members' expressions. In Experiment 2, participants categorized fearful and happy expressions as being either positive or negative using a mouse-tracking paradigm. Participants exhibited the most direct trajectories toward the "positive" label for ingroup happy expressions and an initial attraction toward positive for ingroup expressions of fear, with outgroup emotion trajectories falling in between. Experiment 3 replicated Experiment 2 and demonstrated that the effect could not be accounted for by targets' gaze direction. Overall, people judged ingroup faces as more positive, regardless of emotion, both in deliberate and implicit judgments. (PsycINFO Database Record

By many accounts cooperation appears to be a default strategy in social interaction. There are, however, several documented instances in which reflexive responding favors aggressive behaviors: for example, interactions with out-group members. We conduct a rigorous test of potential boundary conditions of intuitive prosociality by looking at whether intuition favors cooperation even towards competitive out-group members, and even in losses frames. Moreover, we address three major methodological limitations of previous research in this area: a lack of an unconstrained control condition; non-compliance with time manipulations leading to high rates of exclusions and thus a selection bias; and non-comprehension of the structure of the game. Even after eliminating participant selection bias and non-comprehension, we find that deliberation decreases cooperation: even in competitive contexts towards out-groups and even in a losses frame, though the differences in cooperation between groups was consistent across conditions. People may be intuitive cooperators, but they are not intuitively impartial.

In certain threatening social encounters, humans seem to act distrustfully, uncooperatively, even aggressively by default, and must reason themselves towards comity and moderation. Yet, the contemporary scientific literature mostly supports the opposite view, according to which we are “intuitively prosocial”: acting cooperatively by default in positive-sum interactions in games such as the Prisoner’s dilemma. Could a change in the nature of the game elicit a different profile of default behavior? Across four studies we investigate whether intuition might also favor defensive aggression. We develop a “pre-emptive strike game” in which two players make a series of decisions about whether to live-and-let-live, or instead pay a small cost to imposing a large cost on the other player, knocking them out of the game. In this setting we find that default aggression prevails. Moreover, this aggressive tendency can be overridden when playing the game against in-group members, but tends not to be when playing against out-group members. In short, when faced with a social partner who may choose to harm them, people default towards defensive aggression.