"When two persons interact, they continually negotiate two major relationship issues: how friendly or hostile they will be with each other, and how much in charge or control each will be during their transactions" (Kiesler and Auerbach 2003: 1712). Social interactions can be mapped onto two main dimensions that are perpendicular to each other: the affiliation dimension -also called the horizontal dimension (Hall, Coats, and Smith LeBeau 2005), which is characterized by friendliness and warmth on the one end of the dimension and by hostility and aggression on the other end; and the control dimension -also called the vertical dimension -which relates to differences in power, dominance, and influence among two or more social interaction partners (Kiesler and Auerbach 2003;Moskowitz 1993;Tiedens and Jimenez 2003;Wiggins 1979).The vertical dimension of social interactions is present in nearly every social context. We live in a hierarchically organized society in which a member of the parliament is considered a higher status person than a janitor. We are confronted with hierarchies at our workplace when interacting with superiors, peers, and subordinates. Even among friends and family members the power dimension often plays a role. Not all hierarchies are explicit such as they appear in a company's organizational chart. Many hierarchies are more subtle, for instance as when an individual succeeds in convincing his or her group of friends to go watch a particular movie.The vertical or hierarchy dimension affects how we relate to others and it thus greatly impacts on real world outcomes. As an example, the status difference between an airplane captain and the other cockpit members (first officers and flight engineers) can entail ineffective communication leading to human error and ultimately to catastrophe. When an airplane crashes because the higher power position of the captain does not encourage the crew members to voice 2 their concerns or observations about flight irregularities, the hierarchical relationship can contribute to disaster.To maximize effective communication among members possessing different levels of power or status, not only the verbal content of a message is important but also the way the information is conveyed nonverbally plays a role. In the present chapter, we will focus on how the vertical dimension is linked to nonverbal behavior. We will review the expressed nonverbal behavior of people who differ on the vertical dimension and the perception of verticality based on the observation of people's nonverbal behavior. We will also discuss whether people are accurate in judging others' power and dominance. We will present the nonverbal behaviors that are associated with persuasion and we will talk about how nonverbal dominance affects interpersonal relationships and interactions. Finally, we will review individual characteristics that have been shown to moderate the expression or perception of power and dominance.
Definition of the terms used to describe the vertical dimensionWe focus on the interp...