This thesis describes a program of research designed to investigate the sensitivity of perceivers to the ontological distinctions between simulated expressions of happiness unrelated to positive emotional experience, or, posed smiles, and spontaneous, veridical expressions of positive affect, or, genuine smiles. Importantly, this research was conducted from within the theoretical framework of Gibsonian ecological psychology, an alternative approach to the information processing theories that dominate contemporary psychological theorising. Four experiments were conducted that employed an original set of ecologically valid facial displays generated specifically for the present research. In Experiments I a and 1 b, it was demonstrated that when jUdging from either photographs or video, participants could determine whether a smile reflected a positive emotional experience or not. Furthermore, for both of these studies, participants exhibited a bias toward misidentifying posed smiles that expose the teeth as genuine smiles. Experiment 2 also revealed findings consistent with the notion that perceivers are sensitive to the meaningful differences between posed and genuine smiles. In this study, participants were required to judge the valence of a series of target words, each of which was preceded by a briefly presented facial expression (i.e. a prime). The results of this study indicated that the identification of positive words was facilitated when preceded by a genuine smile, but not a posed smile. Experiment 3 was conducted to further investigate how such sensitivity may be manifest in regard to guiding effective social interaction. PartiCipants were required to play several rounds of the Prisoners' Dilemma game with partners (actually video recordings) exhibiting Xll either posed or genuine smiles. The results of this experiment indicated that genuine smiles facilitated cooperative interaction, but posed smiles did not. The results of all four experiments are discussed in terms of the functionality provided by accurate social perception with regard to the acquisition of information specifying the emotional state, and more broadly, the dispositional properties of conspecifics. Finally, these results will be considered in terms of the ecological conceptualisation of psychological activity, with an emphasis on the social affordances specified by posed and genuine smiles respectively.