Edward Thorndike (1874 - 1949) is known for his work on Learning Theory. He studied how cats learned to escape from a puzzle box, which led him to conclude that the cats solved this problem through a gradual process of learning through trial and error, rather than by using insight. He proved this by plotting how long it took for the animals to escape, and showing that the animal escaped quicker with each trial, thereby producing a gradual learning curve.
His work with animals led him to formulate the Law of Effect, which states that when a behavior is followed by a desirable consequence, it becomes associated with that situation so that the behavior becomes more likely to be performed when the same situation is encountered. In the puzzle box experiment, the cat finds itself in a situation where it is trapped in a box. If the cat was able to escape by pushing on the door, then it will likely do the same thing when it is put back in the box. Conversely, if a behavior is followed by an undesirable consequence, then that behavior becomes less likely to be repeated.
Thorndike's work later led to the development of Operant Conditioning, a type of learning which involves forming an association between one's behavior and its consequences.