Humans are fundamentally social creatures, who must interact with, and depend on, conspecifcs to survive. Adaptive characteristics, in this context, thus include the ability to coordinate, and work with others - which requires one to be able to communicate, and to understand others' communications - and the willingness to trust (along with a healthy skepticism of others, and the ability to identify any reliable signals of trustworthiness - or a lack thereof). That we, as humans, have such abilities is obvious, but the way in which we are able to coordinate and communicate, and to pick good interaction partners, is still, in many ways, a mystery: There are large literatures describing many facets of the interpersonal perception process - for example, the perceptual basis of different types of evaluations that we might make of others - but there are many others that we simply do not yet understand - for example, why we tend to weight our first impressions of other people so heavily, even after we get to know them. The goal of this thesis was therefore to try to address some of these questions that remain.