John B. Watson conducted the ‘Little Albert’ experiment on fear conditioning. In 1920, Watson and his graduate assistant Rosalie Rayner studied whether fear could be learned by pairing a neutral object with a frightening noise. Their subject, a nine-month-old infant known as Little Albert, initially showed little fear of a white rat. After the rat was repeatedly paired with the loud strike of a metal bar, Albert reacted fearfully when presented with the rat alone.
The study was designed to apply classical-conditioning principles—associated with Ivan Pavlov’s earlier work with dogs—to human emotional responses. Watson and Rayner also reported fear responses toward several furry objects, a phenomenon interpreted as stimulus generalization.
Watson is the canonical answer because he designed and led the research, although Rayner was an essential co-researcher. The experiment is now remembered as controversial: it involved a child, lacked modern safeguards, and did not fully remove the conditioned fear. Later scholarship has also questioned the study’s details and the identity and health of Little Albert.