Milena Dzhelyova PhD thesis (with chapters 2-6 removed)

The pro-sociality of humans is manifested by the existence of cooperation in levels not common with any other species. Previous studies suggest that snap judgements of individuals are enough to determine if someone is a potential partner for cooperation. In addition to the often studied facial characteristics affecting cooperativeness and trustworthiness attribution (kin resemblance; attractiveness and emotional expression), the experimental work reported here examined the influence of head posture; gaze direction and skin colour on the attribution of trustworthiness and cooperation. A slightly tilted head (less than 3° downward) increased the perception of cooperativeness, especially for male and hostile looking faces. The importance of head tilt increased with decreased self-assessed dominance. Furthermore, even though some evidence that the effect of head posture is independent of gaze direction was found, gaze direction was also a strong indicator of cooperative intentions. Direct gaze and gaze slightly looking down (3°) were perceived as more cooperative than deviations of gaze outside this range (3° up or 6°9° down). Skin colour, a putative cue to current health status, was also found to impact on trustworthiness perception with a healthy skin colour increasing trustworthiness ratings. Additionally, as cooperative and trust decisions are vital for survival and social interactions, decisions based on facial appearance are made quickly and automatically as demonstrated by a trustworthiness modulation on an early face related component with 170 ms of exposure. Collectively, these findings suggest that facial characteristics employed to infer trust and cooperativeness help the observer to assess the motives and intentions of the individuals and assist the choice of partners that will lead to increased benefits and reduced costs in collaborative actions. Such considerations fit well with the evolutionary theory of cooperation as reciprocated social exchange.