Despite the strictures of the extreme Behaviourists, psychologists have been taking an increasing interest in the development of theories concerning the 'mechanisms' internal to humans and animals which permit perceptual, memory, and problem solving behaviour. One consideration which has enormously stimulated an interest in theories of internal cognitive represen- tation has been progress in the theory and the technology of computing machines, which has opened the promising prospect of computer simulation of human and animal psychological functions. What has developed is the possibility of...