Whisper : a computer implementation using analogues in reasoning

This thesis concerns the use of an analogue as an aid to a problem solving program. A -working system, the advantages of the analogue it uses, the mechanisms required, and the interaction of ether forms of knowledge are described. The program, WHISPER, uses a diagram together with procedures for modifying it, as an analogue of a situation involving a stack of arbitrarily shaped rigid bodies. It determines a stack's stability and predicts the motions cf any unstable object by examining the situation's diagram. The analogue is particularly valuable in detecting discontinuities in an object's motion. For example, collisions with other objects or cliffs an object might slide over can be 'seen' in the diagram rather than having to be inferred from a description of the situation. WHISPER uses a simulated parallel processing 'retina' to look at the diagram which is encoded in a two-dimensional array. It consists of a fixed number of processors operating in parallel and communicating only with their immediate neighbours. WHISPER's retina resembles the human retina in some respects. Its resolution decreases away from its center. It can be moved to fixate on different sections of a diagram. A set of domain independent features are extracted from WHISPER's diagrams by procedures, called perceptual primitives, which execute on the parallel processing retina. Example features are: symmetry of an object, similarity of two objects, and contacts of an object with ether objects. In addition to these primitives, the retina can be used to 'visualize1 the rotation of an object without having to move it directly in the diagram The advantages of analogues are classified in terms of two categories according to whether a correspondence exists between the behaviour of the analogue and the behaviour of the external situation, or whether a correspondence exists between the static configurations of the analogue and those of the external situation. Some reasons for the effectiveness of analogues are presented.