Before 1920 
  The Future

  Before 1920:
Empirical Knowledge Base for Education

This material is provided by Robert Kentridge, University of Durham, England.
His complete lecture may be found at:

Edward Thorndike, puzzle-boxes and the law of effect.

You may recall that we left comparative psychology's development as an empirical response to Darwin's 'Descent of Man' very much on the verge of becoming a science. The importance of the problem and the practical difficulties had been recognised and, by the end of the century, serious efforts were being made to produce objective tests of animal intelligence.

The focus of this work was now America where the publication of William James' 'Principles of Psychology' (1890) inspired a growing number of graduate-students. One, Edward Thorndike, attempted to develop some of the anecdotes on the mechanical problem solving ability of cats and dogs collected by George Romanes into an objective experimental method. Thorndike devised a number of wooden crates which required various combinations of latches, levers, strings and treadles to open them. A dog or a cat would be put in one of these 'puzzle-boxes' and, sooner or later would manage to escape from it. Thorndike's initial aim was to show that the anecdotal achievements of cats and dogs could be replicated in controlled, standardised circumstance, however, he soon realised that he could now measure animal intelligence using this equipment. His method was to set an animal the same task repeatedly, each time measuring the time it took to solve it. Thorndike could then compare these 'learning-curves' across different situations and different species.

Thorndike was particularly interested in discovering whether his animals could learn their tasks through imitation or observation. He compared the learning curves of cats who had been given the opportunity of observing others escaping from a box with those who had never seen the box being solved and found no difference in their rate of learning. He obtained the same null result with dogs and, even when he showed the animals the methods of opening a box by placing their paws on the appropriate levers and so on, he found no improvement. He fell back on a much simpler trial and error explanation of learning. Occasionally, quite by chance, an animal performs an action which frees it from the box. When the animal finds itself in the same position again it is more likely to perform the same action again. The reward of being freed from the box somehow strengthens an association between a stimulus, being in a certain position in the box, and an appropriate action. Reward acts to strengthen stimulus-response associations. The animal learns to solve the puzzle-box not by reflecting on possible actions and really puzzling its way out of it but by a quite mechanical development of actions originally made by chance. By 1910 Thorndike had formalised this notion into a 'law' of psychology - the law of effect. In full it reads:

"Of several responses made to the same situation those which are accompanied or closely followed by satisfaction to the animal will, other things being equal, be more firmly connected with the situation, so that, when it recurs, they will be more likely to recur; those which are accompanied or closely followed by discomfort to the animal will, other things being equal, have their connections to the situation weakened, so that, when it recurs, they will be less likely to occur. The greater the satisfaction or discomfort, the greater the strengthening or weakening of the bond."

It is worth quoting in full, first because it essentially drove comparative psychology in north America and Europe for fifty years and second because Thorndike maintained that, in combination with the law of exercise, the notion that associations are strengthen by use and weakened with disuse, and the concept of instinct, the law of effect could explain all of human behaviour in terms of the development of myriads of stimulus-response associations. It is worth briefly comparing trial and error learning with classical conditioning. In classical conditioning a neutral stimulus becomes association with part of a reflex (either the US or the UR). In trial and error learning no reflex is involved. A reinforcing or punishing event (a type of stimulus) alters the strength of association between a neutral stimulus and quite arbitrary response. The response is not to any part of a reflex.