Learning by imitation: A hierarchical approach

To explain social learning without invoking the cognitively complex concept of imitation, many learning mechanisms have been proposed. Borrowing an id ea used routinely in cognitive psychology, we argue that most of these alte rnatives can be subsumed under a single process, priming, in which input in creases the activation of stored internal representations. Imitation itself has generally been seen as a "speciaI faculty" This has diverted much rese arch towards the all-or-none question of whether an animal can imitate, wit h disappointingly inconclusive results. In the great apes, however, volunta ry learned behaviour is organized hierarchically. This means that imitation can occur at various levers, of which we single out two clearly distinct o nes: the "action level," a rather detailed and linear specification of sequ ential acts, and the "program level," a broader description of subroutine s tructure and the hierarchical layout of a behavioural "program." Program le vel imitation is a high-level, constructive mechanism, adapted for the effi cient learning of complex skills and thus not evident in the simple manipul ations used to test for imitation in the laboratory. As examples, we descri be the food preparation techniques of wild mountain gorillas and the imitat ive behaviour of orangutans undergoing "rehabilitation" to the wild. Repres enting and manipulating relations between objects seems to be one basic bui lding block in their hierarchical programs. There is evidence that great ap es suffer from a stricter capacity limit than humans in the hierarchical de pth of planning. We re-interpret some chimpanzee behaviour previously descr ibed as "emulation" and suggest that all great apes may be able to imitate at the program level. Action level imitation is seldom observed in great ap e skill learning, and may have a largely social role, even in humans.