« Étude du lien entre les comportements non verbaux émis par de jeunes hommes soumis à un test de stress (TSST) et leur niveau de stress physiologique : influence des expériences passées de maltraitance »

Chronic stress is an important risk factor in the development of a mental health issues. Recent studies seem to show that stress can propagate automatically from one individual to another. Buchanan et al. (2012) have shown that cortisol responses resonate between observers and speakers in an induced stress task (TSST). The cortisol response of observers increased with trait empathy and was not related to the speaker's subjective fear or distress. These results suggest that stress can propagate between several individuals in different social environments: at work, at school or in an interpersonal relationship. This scientific discovery may represent a particularly important issue for professionals who work in health or mental health environments, because they’re in direct contact with stressed individuals.   In the present study, we ask ourselves, what is informing us of the stress level of an individual. Our hypothesis is that we’re able to catch some non-verbal behavioral indicators in stressed individual and that the unconscious perception of these indicators could then trigger an empathic response among the individual who observes it. Our first objective is therefore to analyze non-verbal behaviors (facial expressions and body movement) of 88 men subject to a task of stress validated in laboratory, the Trier Social Stress Task (TSST). To codify facial expressions issued by the participants, the software for automatic detection FACET © of Imotions, Inc. has been used. This software uses the Facial Action Coding System (FACS) developed by Paul Ekman in the 1970s to quantify automatically the units of action underlying the activation of a muscle of the face. To codify non-verbal behaviors of the body, we have asked several independent observers to codify each subjects using the Ethological Coding System for Interviews (ECSI) on The Observer © of Noldus, Inc software. Our hypothesis was that displacement behaviors (see the ECSI, Annexe 2) and certain facial expressions (related to emotions of disgust, fear and anger) could indicate the physiological activation of stress system (measured by salivary cortisol) among our participants.  Our second objective was to analyze whether past experiences of neglect and abuse   could influence the behavioral expression of a person when is stressed. According to the theory of social disengagement of Ekman and Fridlund, when the needs of an individual are unfulfilled by its environment, less it shall communicate them to the latter. Therefore, individuals who have been neglected or abuse in their childhood may be less expressive.  No association is detected between the non-verbal behaviours and the level of physiological stress when it does not take account if a participant has been neglected of abused. By contrast, the individuals in our sample who were maltreated demonstrate less facial expressions of joy, contempt, disgust and sadness when their stress responses were higher. While individuals not mistreated showed more facial expressions of joy, surprise and fear when their stress response were higher.  Our last objective was to assess if naive observers (without grid or special training) could assess the level of stress of the individuals in our sample. We have therefore asked two observers to codify the mood and the level of stress of 51 participants.  Results tend to suggest that our two observers are not able to evaluate consciously the stress level presented by participants in our study, but are able to identify a lesser frequency of facial expressions of sadness and disgust when a person is under stress.

Keyphrases: TSST, FACET, Comportements non-verbaux, Non-verbal behaviors, Facial expressions, Abuse and neglect, Salivary cortisol, Chronic stress