An affordance in ecological perception is the functional utility of any environment for a person with certain action capabilities. Specifically, it is the combination of environmental properties that supports some activity for a particular persov. Affordances are thereby based in material properties of person and environment and they are perceived. The central hypothesis of this study is that perceptual judgement on interior space reflects the underlying dynamics of activity in the person-space system, specifically that perceptual category boundary for certain activity corresponds to actual critical point. Second, this percieved point is constant over body scale changes in the system. This parallelism between perception and action implies that predictions can be made about action performance from an analysis of the perceptual judgement. In the case of living room and bed room size, this means that the perceptual category boundaries between