What are affordances? How are they generated? What resources might we employ to investigate and to reveal affordances? Affordances have been described as action relevant properties of objects (Gibson, 1979). As such, they would be related to abilities. Often cited examples of affordance properties are 'graspability', 'climbability', and 'sitability' (Gibson, 1979; Mark, 1987; Mark, Balliett, Craver, Douglas & Fox, 1990; Turvey, Shaw, Reed & Mace, 1981; Warren, 1984). Judging from these examples it would seem that affordances can be listed by combining common action verbs (that is, 'to grasp', 'to climb', 'to sit', 'to walk', 'to chew', and so on) with 'ability' as a suffix signifying 'able to be grasped', 'climbed', 'sat upon', and so forth. However, there may actually be no single affordance property corresponding to any one of these terms! We will explore this possibility in the case of 'graspability'. Despite the possible lack of a property corresponding to 'graspability' or other '-ability' terms as such, research has shown that affordance properties exist, nevertheless (Bingham, Schmidt & Rosenblum, 1989; Carello, Grosofsky, Reichel, Solomon & Turvey, 1989; Gibson, Riccio, Schmuckler, Stoffregen, Rosenberg & Taormina, 1987; Mark, 1987; Mark, Balliett, Craver, Douglas & Fox, 1990; Warren, 1984; Warren & Wang, 1987). The research on center of mass perception1 that we will report in this paper will provide additional evidence for the perception of affordance properties.
Affordances are perceptible properties. The study of affordances is part of the study of perception. 'Grasp', 'climb', and 'sit' are natural language terms. Undoubtedly, some affordance properties are related in some fashion to the types of events one intends by reference to 'grasping', 'climbing', and 'sitting'. However, the nature of the relation between perceptible properties and natural language terms is a difficult problem that is separate from the problem of discovering perceptible properties and describing their basis. Furthermore, solution of the perception problem is prerequisite to discovering the nature of the relation between perception and language.
How might affordances be revealed? We suggest that dynamics provides an analytical basis from which to begin.