The first 30 seconds: Trustworthiness, Dominance and their neural correlates
A lot has already been written in the blogosphre regarding this study that found the brain regions that are involved in first impression formation. I view the study from a slightly different angle , but first let me introduce the study and its main findings.
The study was focused on finding the brain regions that are involved in the impression formation of a new social entity. We all know that we form automatic and consistent first impressions of strangers we meet based on things like their face to the social information that is available about them. The authors theorized that to know which regions of the brain are involved in evaluating a person for the first time, it would be sufficient to know which regions of the brain were engaged more while the evaluation-consistent information was being processed. To understand this logic, consider the brain regions involved in memory and how they are discovered. Typically, a series of words/images to be remembered are presented to the subjects, while simultaneously their brain are imaged. Later a memory recall/recognition test is administered. It is found that some brain regions are consistently more active during encoding of the original stimuli which are later recalled/ recognized correctly. This effect is know as Difference in Memory effect (DM effect). the fact that these areas are differentially engaged during encoding of remembered stimuli as opposed to forgotten stimuli is taken as evidence for the fact that these brain regions are involved in encoding of memory. Similar to this effect, it is found that evaluations that are consistent with the later overall evaluation of the person engage some brain regions more than when the evaluation is inconsistent with the later overall evaluation. This difference in evaluation effect (DE ) can be used to locate the regions that are involved in social evaluation or formation of first impressions.
Previous studies had indicated that dmPFC was engaged in social evaluation; however many cognitive factors other than purely evaluative factors might be in action here.
It has also been indicated that amygdala is involved in both social evaluation and valence based evaluations and might be involved in these first impression formation. So the authors hypothesized that they would find differential activity in amygdala in consistent as opposed to inconsistent evaluations and this is what they actually observed. They also found that PCC was also differentially engaged while forming first impressions and thus was another brain region involved in evaluating others.
Here is the study design:
To test these hypotheses, we developed the difference in evaluation procedure (see Figure), allowing us to sort social information encoding trials by subsequent evaluations. More specifically, we measured blood oxygenation level–dependent (BOLD) signals using whole brain fMRI during exposure to different person profiles. Each profile consisted of 6 person-descriptive sentences implying different personality traits. The sentences varied gradually in their positive to negative valence (or vice versa) but evoked equivalent levels of arousal. A 12-s interval with the face alone separated the positive and the negative segments. Subsequently, an evaluation slide instructed subjects to form their impression on an 8-point scale. On the basis of these evaluations, we determined which of the presented descriptive sentences guided evaluations (evaluation relevant) and which did not (evaluation irrelevant). For example, if a subject’s evaluation was positive, we assigned the positive segment of the profile to the evaluation-relevant category and the negative segment to the evaluation-irrelevant category. We then identified the brain regions dissociating items from each category (that is, difference in evaluation effect). Notably, we correlated subjects’ BOLD signal with their own individual evaluations. This allowed us to identify brain regions that were consistent across subjects in processing evaluation-relevant information regardless of the particular stimuli that they considered. Immediately after the scanning session, subjects underwent a memory-recognition task.
The results were clear and found that while dmPFC was involved in social evaluations it was not differentially engaged: thus it had a general role to play, perhaps holding the representation of evaluation after it had already been formed; in contrast both amygdala and PCC were differentially recruited and thus underlie the first time evaluations. In the words of the authors:
Understanding the neural substrates of social cognition has been one of the core motivations driving the burgeoning field of social neuroscience. A number of studies have highlighted the dmPFC in the processing of social information. Our results provide further evidence that the dmPFC is recruited to process person-descriptive information during impression formation. However, BOLD responses in this region do not dissociate evaluation-relevant from evaluation-irrelevant information, suggesting that the dmPFC is not essential for the evaluative component of impression formation. In fact, social evaluation recruits brain regions that are not socially specialized but are more generally involved in valuation and emotional processes.
Valuation and emotional processes, as a substantial amount of research has shown, are characteristic of the amygdala. In particular, the amygdala is considered to be a crucial region in learning about motivationally important stimuli. It is also implicated in social inferences that are based on facial and bodily expressions, in inferences of trustworthiness and in the capacity to infer social attributes. Moreover, the involvement of amygdala in social inferences might be independent of awareness or explicit memory. For example, increased amygdala responses were correlated with implicit, but not explicit, measures of the race bias, as well as with presentation of faces previously presented in an emotional, but not neutral, context, regardless of whether subjects could explicitly retrieve this information. Here we provide evidence linking the two domains of affective learning and social processing by showing that the amygdala is engaged in the formation of subjective value assigned to another person in a social encounter.
Although the amygdala is typically implicated in the processing of negative affect and negative stimuli have been shown to modulate it more than positive stimuli, we found that the amygdala processed both positive and negative evaluation-relevant information, suggesting that amygdala activity is driven by factors other than mere valence, such as the motivational importance or salience of the stimuli. This result is consistent with recent findings showing enhanced amygdala responses for both positive and negative stimuli as a function of motivational importance.
Evidence related to the PCC has been more diverse. There have been reports in the social domain, such as involvement in theory of mind and self-referential outward-focused thought33, in memory related processes such as autobiographical memory of family and friends34, and in emotional modulation of memory and attention. More recently, the PCC has been linked with economic decision making, the assignment of subjective value to rewards under risk and uncertainty, and credit assignment in a social exchange. A common denominator of these studies might be that all involved either a social or an outward-directed valuation component. Our task also encompasses these features, extending the role of the PCC to value assignment to social information guiding our first impressions of others.
The amygdala and the PCC are both interconnected with the thalamus as part of a larger circuitry that is implicated in emotion, arousal and learning. Beyond the known role of the amygdala and the PCC in social-information processing and value representation, our results suggest a neural mechanism underlying the online formation of first impressions. When encoding everyday social information during a social encounter, these regions sort information on the basis of its personal and subjective importance and summarize it into an ultimate score, a first impression. Other regions, such as the ventromedial PFC, the striatum and the insula, have also been implicated in valuation processes. However, these regions did not emerge in our difference in evaluation effect analysis. This might suggest a possible dissociation in the valuation network between regions engaged in the formation of value and its subsequent representation and updating. The latter regions would not be engaged during encoding and therefore would not show a difference in evaluation effect but would instead have an effect once the evaluation is formed. The amygdala and the PCC probably participate in both value formation and its representation. The difference in evaluation procedure may provide a useful tool for disentangling the different components of the valuation system and their specific contributions to social versus nonsocial evaluations.
Now I would like to link all this new research with an earlier research on face attributes that found that there were two orthogonal factors that characterize a face- trustworthiness (valence) and dominance. It is important to note that faces are an important mechanism by which we make snap judgments and if it has been found that there are two orthogonal dimensions (found using factor analysis) on which we judge faces and form rifts impressions, there is no reason to suppose that those same two orthogonal factors would not come into play when we form first impressions based on social information and not the face. What I am trying to say is that the non-face social information driven social evaluation would still be structured around the factors of whether the social information pointed to the person as Trustworthy or as Dominant. I would expect that there would be different brain regions specialized for these two functions: We all know too clearly that amygdala is specialized for trustworthiness judgments and that fits in with one of the areas that has been identified for snap judgments. thta leaves us with the PCC, which has normally been implicated in self-referential thinking with an outward and evaluative (as opposed to inward and executive) focus and also a preventive focus. It seems likely that this region would be used to evaluate a social other and judge as to whether he has the ability to execute, harm and dominate oneself. So, what I would like to see is a study that dissociates the scoial information provided to subjects in terms of trustworthiness and dominance factors and sees if there is a dissociation in the evaluative regions of amygdala and PCC; or maybe one can juts factor analyze the results of the original study and see if the same two factors emerge! I am excited,and would love to see these studies being preformed!!
Schiller, D., Freeman, J., Mitchell, J., Uleman, J., & Phelps, E. (2009). A neural mechanism of first impressions Nature Neuroscience DOI: 10.1038/nn.2278
Oosterhof, N., & Todorov, A. (2008). The functional basis of face evaluation Proceedings of the National Academy of Sciences, 105 (32), 11087-11092 DOI: 10.1073/pnas.0805664105
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