The study investigates how emotional stimuli influence our bodily reactions and ultimately make us prone to include or exclude others from our social spher.

The principle on which the study is based is that skin temperature is affected by changes in muscles activity and in blood microcirculation which is controlled by the vegetative nervous system also called autonomous because its activity is largely independent from will.

The research, coordinated by Salvatore Maria Aglioti from the laboratory of Social Neuroscience of Sapienza University, in partnership with Santa Lucia Foundation, is published in the journal Proceedings of the Royal Society B: Biological Sciences.

In order to demonstrate the association between changes in face temperature and the way we categorize people around us, healthy, Italian participants were presented with affective stimuli (e.g. pictures of others in painful or in happy situations)  that could or could not be perceived consciously, called supraliminal and subliminal stimuli respectively. Each affective stimulus was followed by the presentation of photograph of faces that participants had to categorize as Italian or Romanian. By means of an infrared camera measuring with high sensitivity emitted heat from the body, researchers detected the physiological response in the different phases of the experimental task.

It was found a tendency to categorize/perceive unfamiliar faces as closer to our social circle – categorizing them as Italian - after the presentation of positive stimuli and to label faces as more distant from our social circle – categorizing them as Romanian – after the presentation of negative stimuli. Social categorization represents a process through which we code other individuals as ingroup versus outgroup on the basis of different dimensions (ethnicity, religion, ideology) and it is a voluntary cognitive mechanism heavily affected by emotions.

“The results of this study – says Maria Serena Panasiti, researcher at the Department of Psychology of Sapienza University - are relevant for the comprehension of intergroup dynamics and the associated physiological indexes. We demonstrated that emotions, presence or absence of perceptual awareness of positive and negative valence stimuli and the activation of vegetative nervous system largely influence the tendency to categorize the social world according to an ‘us vs them’ based perspective".

The research was supported by the PRIN grant (Progetti di Ricerca di Rilevante Interesse Nazionale, Edit. 2015, Prot. 20159CZFJK) and by EU funding (Horizon 2020-SESAR-2015-1-MOTO: The embodied reMOte Tower, Project Number 699379).

References:
Ponsi G, Panasiti MS, Rizza G, Aglioti SM. Thermal facial reactivity patterns predict social categorization bias triggered by unconscious and conscious emotional stimuli. Proc Biol Sci. 2017 Aug 30;284(1861). pii: 20170908. DOI: 10.1098/rspb.2017.0908.