The belief that the outgroup is less human than the ingroup is seldom consciously endorsed by individuals [(c.f., dehumanisation)] and instead is reflected in the way people tacitly think about the outgroup. Researchers have typically investigated infrahumanisation by looking at the types of emotions people believe ingroup and outgroup members possess . Some emotions are considered unique to humans [(e.g., love, regret, nostalgia)] whereas others are viewed as common to both humans and animals [(e.g., joy, anger, sadness)]. In a series of studies Leyen's and colleagues have widely replicated the finding that people attribute unqiuely human emotions to the ingroup, but not the outgroup. According to infrahumanisation theory, the denial of uniquely human emotions to the outgroup is reflective of the belief that they are less human than the ingroup.
Recent research has investigated how infrahumanisation influences behaviour. In a series of studies Jeroen Vaes and his colleagues investigated people's reactions to outgroup members who attempt to 'humanise' themselves through the use of uniquely human emotions. They found that ingroup members reacted negatively to outgroup members' attempts to humanise, offering less help and withdrawing faster than when the same uniquely human emotion was expressed by an ingroup member or when the outgroup member expressed a non-uniquely human emotion . In an American context, Cuddy and colleagues have investigated the influence of infrahumanisation on intergroup helping behaviour. Examining helping in the aftermath of Hurricane Katrina, Cuddy et al. found that people believed outgroup members experienced less negative uniquely human emotions than ingroup members. Importantly, the degree to which they infrahumanised the outgroup member was related to their report likelihood to offer assistance. Specifically, the more participants infrahumanised the outgroup member the less likely they were to help.