A baby was conditioned to fear a white rat — then everything fluffy or white
In 1920, John B. Watson and Rosalie Rayner paired a loud, startling noise with a tame white rat shown to an infant known as "Little Albert," who initially showed no fear of it. After repeated pairings, Albert became distressed at the sight of the rat alone, and his fear generalised to other white, furry things: a rabbit, a dog, even a Santa Claus mask. It became one of psychology's most famous, and most ethically criticised, demonstrations of conditioned fear.