In 1920, the American psychologist John B Watson published the results of one of the more ethically dubious scholarly articles of the past century. Along with Rosalie Rayner, a 21-year-old graduate student at Johns Hopkins University in Baltimore, where he taught, Watson aimed to instil a specific fear in an otherwise normal baby.
Until then, behavioural conditioning had been exercised solely within the animal realm, but Watson and Rayner selected a nine-month-old boy they called ‘Albert’ for their study, paid his mother a dollar, and placed a variety of small, live animals in front of him, including a rat – in which he initially showed a playful interest. As Albert played with the rat, the experimenters hit a nearby steel bar with a hammer, emitting a loud noise that scared the boy and made him cry. After doing this a few times, all the experimenters had to do to make Albert burst into tears was to show him the rat. Even without the noise, they successfully conditioned in him a fear of rats, which eventually carried over to a fear of numerous furry creatures, including rabbits and dogs.
More here – Aeon