"Center of Mass Perception": Affordances as Dispositions Determined by Dynamics
Geoffrey P. Binghamand Michael M. Muchisky Indiana University
Affordances are dispositional or relational properties. They consist of properties of objects in relation to properties of a perceiver/actor in the context of a task or a goal to be achieved by way of the affordance ( Gibson, 1979). The basis of the relation unifying object properties into an affordance property is the task goal. Thus, understanding affordances requires some understanding of the manner in which physical properties of object and actor are invoked by tasks.
The relation between affordances and goals is problematic. On the one hand, affordances are task specific. On the other, a given goal might be achieved via various means involving different affordances respectively. The way to resolve this apparent contradiction is via the process of goal specification. Tasks can be analyzed into a sequence of alternative subgoals corresponding to the various ways that the superordinate goal might be achieved. Actual performance of the task requires the successive determination of subgoals. How might such goal specification proceed? Goal specification entails the perception of affordances corresponding to subgoals. The implication is that there are superordinate and subordinate affordances. The problem is to understand the relation between the former and the latter. For instance, a goal might be to transport an object from a table to a shelf. Suppose that one recognizes that the object affords being so transported by oneself. That is, the size and weight and surface properties are such that