Two separate issues were looked at in this experimental study of the semantics of spatial prepositions. In the context of work to specify general factors of a functional geometry mediating the use of spatial prepositions (Garrod & Sanford 1989; Coventry 1992, 1993), object-specific effects were investigated. Subjects described video scenes of various objects and their responses of in, on, over, and beside were monitored. The independent variables involved the manipulation of functionality specific to various types of objects. It was concluded that knowledge about how particular objects interact with each other contributes to the representation of functional relations which determine preposition usage. Therefore a specification of functional geometries cannot proceed without a prior formulation of our knowledge about the physical and social worlds. Additionally two different experimental measures of prepositional covariance with the scenes were used: Lickert-scale judgements and sentence completions. Responses from two separate groups were compared. The findings indicated some agreement between the two measures, but also some differences in patterns of response. It is suggested that the measures are tapping different processes, and that a variety of methods need to be used to abstract to lexical representation.