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One of the earliest explanations of how ( animals, children, elderley ) and humans learn was proposed by ( Pavlov, Skinner, Bandura ) in 1927. He noticed that when a ( dog, cat, horse, baby ) he was studying heard the food buckets being brought it salivated. He knew this was a ( reflex, primitive, normal ) response but he also realised that the dogs had learnt to salivate at the sound. This encouraged him to try to make them salivate in response to another event. He set up trials over a few days and each time the dog was fed a bell was rung. Eventually the bell was rung even when no food was offered and he found the salivation amount was the same as when food was present.