The American psychologist Edward Lee Thorndike (1874-1949) is known as the father of modern educational psychology. His landmark dissertation, Animal intelligence: An experimental study of the associative processes in animals, published in 1898 (when he was only 23) marks the beginning of the experimental analysis of behavior ( ).
Thorndike studied animal behavior through painstaking empirical work with cats in "puzzle boxes" - cages which he constructed to allow the animals to escape by different actions, such as pushing a lever or pulling a loop of string. The animals were rewarded with food upon successful escape. By observing and timing repeated escape episodes, he discovered that a cat would learn to escape through trial and error. His experiments showed a gradually declining time curve exhibiting no sudden drop which would indicate comprehension through reasoning on the part of the animal, leading him to formulate the law of effect.