John B. Watson (1878-1958) was mainly responsible for initiating the behaviorism movement in the first decades of the 19th century. Watson was a positivist thinker and therefore insisted on a new psychology based on observable facts that can be described objectively. Thus, he refused to accept mentalistic concepts or terms, such as consciousness. Partly, impetus for the idea of behaviorism came from experiments with animals. Jacques Loeb (1859-1924) came up with his concept of tropism, which hold that the presence of a stimulus forces the animal to respond—thereby he eliminated the need for consciousness in an animal. On the other hand, Loeb argued that there is an associative memory that is a network of stimulus-response connections. Hence, animals have the ability to form these connections (or to learn) consciously.
The tale of the horse Clever Hans is probably one of the best examples to illustrate the general problem of psychology in the 1900’s. Misconceptions of mind and consciousness became visible with the appearance of the famous phenomenon Clever Horse that apparently could answer complex questions such as: “How many of the gentlemen present are wearing straw hats?” The answer was given through the horse tapping with its hoof; however, as found out later, the horse learned to tap on the ground whenever it saw a downward movement of the trainer’s head. The example of Clever Hans had proofed again the necessity for the Law of Parsimony stated by Conwy Morgan (pg.145).
Another contributor to the objective experimental approach was Edward Lee Thorndike (1874-1949) who conducted intensive research with animal learning. His main theory was Connectionism that characterized learning as drawing connections between situations and responses. “…Learning is connecting. The mind is man’s connection-system” (pg.235). Today, Thorndike’s connectionist theory is widely supported in the field of AI when modeling human behavior with machines. Thordike explained learning on the basis of trial-and-error learning; the method by which human as well as animal learning is based on. “…Response tendencies that lead to success are stamped in after a number of trials” (pg. 236). The term “stamped in” can be replaced with “more likely to recur”. He also introduced the Law of Effect and the Law of Exercise. The Law of Effect can be seen as the precursor of the reinforcement theory: “acts that produce satisfaction…become associated with that situation…” (pg.237). The Law of Exercise refers to the effect of repetition on memory. More precisely, and referred to his connectionism theory, the connection between situation and response would strengthen after each successive trial.
Ivan Pavlov (1849-1936) is the main reference for most psychology introductory textbooks in the chapter of behaviorism. His concept and his experiments with conditioned reflexes were one of the main bases for following behaviorist theories. In his experiments with dogs, he discovered that reflexes could be elicited by any other stimuli. Additionally he added the effect of reinforcement on this fact. If the dogs were fed for the desired response, the likelihood for this response increased. Similarly, Vladimir Bekhterev (1857-1927) explained the phenomenon of conditioned reflexes as associated reflexes.