One of the earliest and best replicated findings resulting from the experimental investigation of animal learning is that conflict can produce disordered behaviour (Pavlov, 1927). These conflicts vary in kind, ranging from a conflict, as in the circle and ellipse discrimination experiments, between responding and not responding, to a conflict between approach and avoidance as in the pairing of electric shock with food. As Kimmel (1971) points out, whether or not a conflict produces disordered behaviour is a function of the animal's previous history. An ellipse has already to be clearly associated with ‘no food’ and a circle with food for disorder to be produced by presenting a circle and ellipse which are very similar to each other. Similarly, special conditions of training can be found which enable a dog to salivate and wag his tail in response to an injury severe enough to draw blood.